Wildfire in a Warming World: Part 2

(click here to download a pdf of this complete article or a one-page synopsis)

By Jennifer Hushaw & Si Balch

In Part I, we discussed the recent rise in U.S. wildfire, the evidence suggesting climate is a major driver of that increase, and the reality that future increases in temperature and drought frequency (in some regions) will lead to greater fire potential, especially in moisture-limited ecosystems. There is no question that wildfire risk has changed (and will continue to change) research-update-boxas a result of on-going climate change. Importantly, the anticipated shifts in fire will have big implications for commercial forests and conservation lands alike, as well as implications for the climate system itself because wildfire acts as a positive feedback that accelerates terrestrial carbon emissions. Severe disturbance caused by novel fire regimes may also hasten the species shifts expected with climate change, making fire an important driver of ecosystem change in both the near- and long-term.

In Part II, we describe the latest research on future changes in fire frequency, extent, and/or severity, as well as discussing management strategies and outlining some useful information sources.

Overview of Changing Fire Risk


Fire potential and the length of the fire season are projected to increase in many regions. These changes will be driven by earlier snowmelt, warmer temperatures (particularly summer), drought stress, and changes in soil water content (Keane et al. 2015; Waring and Coops 2016; Young et al. 2016) associated with climate change.

In the continental U.S., the potential for very large fires (>12,355 acres) is strongly linked to meteorological and climatological conditions. Recent research indicates that the potential for very large fires will increase in historically fire-prone regions as a result of climate change, while other regions will experience an earlier start or an overall extension of the fire season as atmospheric conditions become conducive earlier in the year and persist later (Barbero et al. 2015) – see details in The North American Outlook (below).

Drier fuels will also increase fire potential because fuel moisture is highly sensitive to temperature. For example, a recent analysis in Canada found that for each additional degree of warming, a 5 to 15% increase in precipitation is required to maintain fuel moisture, depending on the type of fuel in question (i.e. fine surface fuels, duff layers, or deep organic soils) (Flannigan et al. 2016). In the absence of a sufficient precipitation increase, these fuels begin to dry out and move closer to critical thresholds for fire ignition and spread. In fact, Canada is expected to have more days of extreme fire weather because future precipitation will be insufficient to compensate for the drying associated with warmer temperatures – this is true even for future scenarios with the greatest precipitation increase (i.e. 40%) (Flannigan et al. 2016).

Some of these changes will be non-linear, leading to dramatic increases in fire frequency or severity in some regions once critical thresholds are crossed. A great example can be found in the boreal forest and tundra ecosystems of Alaska where there are distinct temperature and moisture thresholds[1] for fire occurrence that will likely be crossed by the end of this century, significantly increasing the probability of wildfire and potentially leading to novel fire regimes in those areas (Young et al. 2016).


Climate-induced changes in vegetation (including type, density, large scale die-off, etc.) and forest pests will also influence fire risk by affecting fuel loads.

As we discussed in a previous bulletin, climate change will affect the population dynamics and spread of many forest pests and diseases, including mountain pine beetle. Mountain pine beetle outbreaks can, in turn, alter the quantity and characteristics of both live and dead fuels by changing the amount of fuel in the forest canopy, the base height of the canopy, the amount of surface fuel, and other aspects of forest biomass. In this way, they can influence fire probability, severity, and rate of spread, as well as the potential for crown fire (Hicke et al. 2012).

Climate change will also have direct effects on vegetation and forest biomass through long-term shifts in species distribution and forest composition, as well as small- and large-scale mortality events brought on by drought and other extremes. In Part I, we detailed how drought and beetle-induced mortality in western U.S. conifers is already contributing to an increase in fire. These mortality events and longer-term vegetation changes can flip an ecosystem from being fuel- to moisture-limited (or vice-versa), changing what controls fire activity in a given region (as discussed in Part I).

In some cases, the changing fire regime itself will cause vegetation communities to shift or flip from a moisture- to fuel-limited ecosystem. For example, the fire return interval in the greater Yellowstone ecosystem is predicted to decrease (i.e. more frequent fire) to the point that some forested areas will no longer be able to regenerate by mid-century and will instead convert to a new dominant vegetation type that shifts the region into a fuel-limited fire regime (Westerling et al. 2011).

“The bottom line is that we expect more fire in a warmer world.”  (Flannigan et al. 2016)


Modelling Future Wildfire


Globally, fire probability is expected to increase in the mid- to high-latitudes and decrease in the tropics, with these changes becoming more pronounced later in the century. In the near term (i.e. 2010-2039), the most consistent increases will occur in places with an already somewhat warm climate, but there are also major uncertainties in the next few decades. There is more confidence in projections for the end of the century (i.e. 2070-2099) when climate models have a higher level of agreement in their projections because the magnitude of climate change will be even greater, with some locations experiencing an average change in fire probability up to +0.25 (Figure 1; Moritz et al. 2012).

Flannigan et al. (2009) also suggest that a general increase in area burned and fire occurrence is likely, based on their review of close to 50 studies conducted between 1991 and 2009 on future fire activity around the world. Although these studies focused on different fire activity metrics, time frames, and locations, more than three-quarters of the analyses pointed to an increase in fire activity. In particular, they noted that fire seasons are lengthening in temperate and boreal regions and this trend should continue in a warming world.


Most of the research conducted to date in North America points toward a future increase in wildfire, with longer fire seasons and greater fire potential due to more conducive atmospheric conditions in a number of regions (Barbero et al. 2015; Wang et al. 2015; Liu et al. 2013; Young et al. 2016).

For example, in a study mentioned above, researchers from the University of Idaho, the US Forest Service, and the Canadian Forest Service modelled future potential for “very large fires” in different ecoregions due to climate change and they found the potential for very large fires will increase in the continental U.S. The largest absolute increases were predicted for the intermountain West and Northern California, while the largest relative changes were predicted in the northern tier of the country where the potential for very large fires has historically been quite low (e.g., see Barbero et al. 2015, Figure 1). In addition, their analysis suggests the southern U.S. will have an earlier fire season in the future, while the northern regions will experience an overall lengthening of the fire season, with an extension of potential burn days at both ends of the season. These changes are driven by anticipated increases in fire danger and temperature, as well as decreases in precipitation and relative humidity during the fire season (Barbero et al. 2015).

Another study by Liu et al. (2013) used results from a downscaled climate model to evaluate how fire potential will change by mid-century (2041–2070), as measured by the Keetch–Byram Drought Index (a commonly used index designed specifically for fire potential assessment). They predict an increase in fire potential in the Southwest, Rocky Mountains, northern Great Plains, Southeast, and Pacific coast due to warming trends, in addition to longer fire seasons in many regions.

Looking farther north, the research also suggests increases in fire potential across high-latitude regions. Specifically, the annual number of fire spread days in Canada is expected to increase anywhere from 35–400% by 2050, with large absolute increases in the Boreal Plains of Alberta and Saskatchewan and the greatest relative change in coastal and temperate forests (Wang et al. 2015). Similarly dramatic increases in fire activity are predicted for areas of Alaska with historically low flammability in the tundra and tundra-forest boundary areas, with “up to a fourfold increase in the 30-yr probability of fire occurrence by 2100” (Young et al. 2016).

Fire potential is not the only metric we might be concerned about, however. There are also questions about how fire severity may change as a result of climate change. Although fire severity will increase in some cases, as we have seen in the western U.S. with high fuel loads and exceptional drought conditions, future conditions may also decrease fire severity. When some researchers incorporated climate-induced changes in vegetation type, fuel load, and fire frequency, rather than climatic changes alone, they found that a widespread reduction in fire severity was likely for large portions of the western U.S. (Figure 2; Parks et al. 2016). This is because future increases in fire frequency and water deficits will reduce vegetation productivity, the amount of regeneration, and the amount of biomass accumulation on the landscape—all of which contribute to decreased fuel loads that will no longer support high-severity fires (Parks et al. 2016).

Management Considerations  


When considering how to address these wildfire regime shifts, one approach is to “manage for the extremes,” rather than the average fire event or return interval in a given region, because it is the extremes that determine the necessary capacity of fire management organizations and, although these extremes cannot be as easily predicted, they can have serious consequences (Wang et al. 2015; Irland 2013).


In terms of forest management, fuels reduction via pre-commercial or commercial thinning operations and prescribed fire is an obvious strategy for dealing with increased fire potential. That said, fuels reduction is better suited for some forest types than others, namely fuel-limited forest communities (Steel et al. 2015), e.g. yellow pine and mixed conifer forests in California or piñyon-juniper woodland and lower montane forests (dominated by ponderosa pine) in the Rocky Mountain region. In systems where the fire regime is primarily moisture- or climate-limited, a reduction in fuels will not be as effective at reducing fire hazard because fuel is not the limiting factor.


An argument can also be made for taking a more passive approach that “lets nature take its course,” where the fire regime is allowed to change and it ultimately shifts the dominant vegetation type to something new (as discussed above). In this case, the natural disturbance regime eventually transitions plant communities into a state of equilibrium with the new climate (Parks et al. 2016). This approach may ultimately be more appropriate and cost-effective in locations where conditions are expected to become more arid and fire frequency is projected to increase dramatically, compared with resisting change through on-going, active fire suppression efforts. Although not appropriate for most commercial operations, the passive approach may be a consideration for lands with a management focus on maintaining resilient transitional habitat for wildlife in a changing climate.


Of course, it is worth noting that these anticipated changes in wildfire are happening in the larger context of land use change (more development in the wildland urban interface, greater forest fragmentation), fuel accumulation (due to historic fire suppression efforts, landowner reluctance to harvest, and/or insufficient budgets for fuel treatments), and infrastructure/industry changes (lack of “fire wise” development in some regions, loss of institutional firefighting operations with ownership change).

Things to Do

A number of common practices can help land managers prepare for fire risk, which will be important to emphasize (or implement) in the face of increased fire potential. These include:

  1. Put all foresters and other field personnel through the state forestry department’s basic fire training school.
  2. Have the state forest service phone numbers and radio contact on everyone’s cell phone.
  3. Equip everyone’s truck with Indian tanks and fire rakes.
  4. Know who has bulldozers, where they are, and how to reach their owners.
  5. Identify water sources for pumping.
  6. Identify water sources for water bombers.
  7. Identify landing zones for helicopters.
  8. Think about how to communicate with abutting home owners about fire risk. This interface of houses and trees is an increasingly dangerous situation for both the forest owner and home owner.
  9. Utilize the resources below to find up-to-date information on potential fire risk.

Additional Resources

  • A program that produces landscape-scale geospatial products for planning, management, and operations, including maps and databases that describe vegetation, fuel, and fire regimes. Website provides data, reports, tools, maps, etc.
  • www.landfire.gov
  • Source: USDA Forest Service & US Department of Interior
National Interagency Coordination Center
  • NICC coordinates interagency wildland firefighting resources. They also dispatch Incident Management Teams and resources as necessary when fires exceed the capacity of local or regional firefighting agencies. Website provides Incident Information with daily updates on large fires and Predictive Services, such as weather, fire fuels danger, outlooks, etc., as well as other resources for wildland fire and incident management decision-making.
  • www.nifc.gov/nicc
  • Source: Multi-agency organization, including: BIA, BLM, USFS, USFWS, NASF, & NPS
FRAMES (Fire Research and Management Exchange System)
  • A searchable online portal for fire-related information, including documents, tools, data, online trainings, discussion forums, announcements, and research, as well as links to numerous other fire-related websites and portals for regionally-specific sites and resources.
  • www.frames.gov
  • University of Idaho; USFS Rocky Mountain Research Station
Joint Fire Science Program (JFSP)
Geographic Area Coordination Centers
  • Web-portal for incident information, logistics, predictive services (e.g. information about weather, fuels and fire danger), and administrative resources for wildland fire agencies.
  • http://gacc.nifc.gov 
  • Source: Geographic Area Coordinating Group (GACG) – interagency; made up of Fire Directors from each of the area Federal and State land management agencies
  • Portal to numerous websites and resources related to wildfire risk and detection, including many listed in this table and others.
  • www.drought.gov/drought/data-maps-tools/fire
  • Source: Multi-agency, including: FEMA, EPA, Dept. of Interior, Dept. of Commerce, NOAA, DOE, USDA, and Army Corps of Engineers
  • Educational resources on wildfire prevention and “firewise” practices for homeowners and professionals, including state-specific information for New England and adjacent Canadian provinces.
  • www.northeastwildfire.org
  • Source: Northeast Forest Fire Protection Commission’s Prevention and Education Working Team
Wildfire Risk Assessment Portals
  • Several states/regions have these websites, which include web-mapping applications showing fire risk and assessment, as well as information on historic fire occurrence and information for developing community wildfire protection plans.
  • Source(s): State forest service, state forester, universities, etc
Active Fire Mapping Program
  • Provides near real-time, satellite-based detection and characterization of wildland fire conditions in a geospatial context for the continental United States, Alaska, Hawaii and Canada.
  • http://activefiremaps.fs.fed.us/index.php   *soon moving to new URL: https://fsapps.nwcg.gov/afm
  • Source: USDA Forest Service Remote Sensing Applications Center
Historic Wildfire Occurrence Data
  • This data product contains a spatial database of wildfires that occurred in the United States from 1992 to 2013, generated for the national Fire Program Analysis (FPA) system. The wildfire records were acquired from the reporting systems of federal, state, and local fire organizations.
  • www.fs.usda.gov/rds/archive/Product/RDS-2013-0009.3/
  • USDA Forest Service
Global Maps of Fire Risk
  • This on-line map viewer of satellite-derived global vegetation health products, includes one for fire risk that is updated continuously. You can also go back and see archived maps from previous dates.
  • www.star.nesdis.noaa.gov/smcd/emb/vci/VH/vh_browse.php (choose “Fire Risk” under the Data Type dropdown menu)
  • Source: Center for Satellite Applications and Research (STAR) – the science arm of the NOAA Satellite and Information Service
National Fire Protection Association
  • Source for national fire codes and standards, public education, and research on fire risk and prevention.
  • www.nfpa.org



[1] Young et al (2016) identified two thresholds for fire occurrence, based on historic data: average July temperatures above 13.4⁰C and annual moisture availability (i.e. precipitation minus evapotranspiration) below 150mm.

~            ~             ~             ~             ~


Abatzoglou, J.T. and Williams, A.P. 2016. Impact of anthropogenic climate change on wildfire across western US forests. PNAS. 113(42): 11770–11775.

Barbero, R., Abatzoglou, J.T., Larkin, N.K., Kolden, C.A., Stocks, B. 2015. Climate change presents increased potential for very large fires in contiguous United States. International Journal of Wildland Fire. 24(7) 892-899.

Flannigan, M.D., Krawchuk, M.A., de Groot, W.J., Wotton, B.M., Gowman, L.M. 2009. Implications of changing climate for global wildland fire. International Journal of Wildland Fire. 18: 483-507.  

Flannigan, M.D., Wotton, B.M., Marshall, G.A., de Groot, W.J., Johnston, J., Jurko, N., Cantin, A.S. 2016. Fuel moisture sensitivity to temperature and precipitation: climate change implications. Climatic Change. 134:59-71.

Hicke, J.A., Johnson, M.C., Hayes, J.L., Preisler, H.K. 2012. Effects of bark beetle-caused tree mortality on wildfire. Forest Ecology and Management. 271: 81-90.

Irland, L.C. 2013. Extreme value analysis of forest fires from New York to Nova Scotia, 1950-2010. Forest  Ecology and Management. 294: 150-157.

Keane, R.E., Loehman, R., Clark, J., Smithwick, E.A.H., Miller, C. 2015. Chapter 8: Exploring Interactions Among Multiple Disturbance Agents in Forest Landscapes: Simulating Effects of Fire, Beetles, and Disease Under Climate Change in Simulation Modeling of Forest Landscape Disturbances. A.H. Perera et al. (eds.) Springer International Publishing. Switzerland.

Liu, Y., Goodrick, S.L., Stanturf, J.A. 2013. Future U.S. wildfire potential trends projected using a dynamically downscaled climate change scenario. Forest Ecology and Management. 294: 120-135.

Moritz, M.A., Parisien, M-A., Batllori, E., Krawchuk, M.A., Van Dorn, J., Ganz, D.J., Hayhoe, K. 2012. Climate change and disruptions to global fire activity. Ecosphere. 3(6):49.

Parks, S.A., Miller, C., Abatzoglou, J.T., Holsinger, L.M., Parisien, M., Dobrowski, S.Z. 2016. How will climate change affect wildland fire severity in the western US? Environmental Research Letters. 11: 035002.

Steel, Z.L., Safford, H.D., Viers, J.H. 2015. The fire frequency-severity relationship and the legacy of fire suppression in California forests. Ecosphere. 6(1): Article 8, 23pp.

Wang, X., Thompson, D.K., Marshall, G.A., Tynstra, C., Carr, R., Flannigan, M.D. 2015. Increasing frequency of extreme fire weather in Canada with climate change. Climatic Change. 130: 573-586.

Waring, R.H. and Coops, N.C. 2016. Predicting large wildfires across western North America by modeling seasonal variation in soil water balance. Climatic Change. 135: 325-339.

Westerling, A.L., Tumer, M.G., Smithwick, E.A.H., Romme, W.H., Ryan, M.G. 2011. Continued warming could transform Greater Yellowstone fire regimes by mid-21st century. PNAS. 108(32): 13165-13170.

Young, A.M., Higuera, P.E., Duffy, P.A., Hu, F.S. 2016. Climatic thresholds shape northern high-latitude fire regimes and imply vulnerability to future climate change. Ecography. 39: 001-012.

Wildfire in a Warming World: Part 1

(click here to download a pdf of the full article or a one-page synopsis)

By Jennifer Hushaw

Wildfire has been a hot topic in the media lately, with California ablaze due to a combination of dangerous fire weather, on-going drought, and scores of drought- and beetle-killed trees. Most recently, the Blue Cut Fire (pictured above) burned 37,000 acres and the Soberanes Fire, which began in late July, is still uncontained and has already burned over 105,600 acres. Of course, severe wildfires are certainly nothing new—take the Great Fire of 1910 that burned 3 million acres or the Miramichi Fire in New Brunswick that burned over 3.8 million acres in 1825—but climate change is creating new cause for concern. In fact, the 2014 U.S. National Climate Assessment says climate change-related fire is increasing the vulnerability of U.S. forests to ecosystem change and tree mortality.

In Part I of this two-part piece, we examine recent trends in fire activity, untangle the role of climate change, and outline the most important aspects of climate that drive fire patterns on the landscape.

The Global Picture

Climate change is expected  to increased wildfire activity in certain regions (IPCC AR5), but, so far, there is little evidence of an increase in area burned or an increase in fire severity for many parts of world, and even some evidence suggesting that, overall, there is less fire on the landscape now than centuries ago (Doerr & Santín 2016).

A 2013 study by researchers at the University of Maryland, the University of California, and VU University in Amsterdam showed this variability in fire trends across different regions (Giglio et al. 2013). They examined global and regional trends in the monthly area burned from 1996 to mid-2012 using information from the fourth generation of the Global Fire Emissions Database (GFED) and they found different, and sometimes opposite, trends depending on the region, as well as a slight decrease in global area burned over the last 16 years (see Figure 1). The study did not analyze what caused these trends, but researchers did offer some insight into the source of year-to-year variability observed in each region. The level of variability relates to ignition and rainfall—regions with fairly consistent fire activity tend to have widespread and routine human-induced burning (mostly for land maintenance) and similar rainfall from year-to-year (e.g. southern and northern Africa), whereas regions with high variability have more sporadic fire ignition (by humans or otherwise) and more variability in the amount of rain from year-to-year (e.g. Equatorial Asia, where fire activity is closely tied to El Niño events) (Giglio et al. 2013).

Wildfire in the U.S.

In contrast to the global picture, we have seen increasing media reports of large wildfires and more discussion of the ballooning cost of fire control efforts in the United States in recent years. This is especially true when conflagrations break out at the intersection of forests and developed lands, also known as the Wildland Urban Interface (WUI). Given the greater cost of suppression efforts and increased risk of damage to lives and property in these areas, some have suggested that the perceived increase in wildfire may simply be due to increased attention. However, as we will discuss below, there is ample evidence that large portions of the U.S. have indeed experienced more fire.

Most studies of wildfire trends in the U.S. are focused on the western part of the country and they have detected an overall increase in fire activity over recent decades. For example, there is evidence that the number of large fires (> 1,000 acres) and/or total area burned per year increased in many parts of the western U.S. from 1984-2011 (Figure 2; Dennison et al. 2014).

Another research team detected a similar trend since 1970, with a noticeable increase in western forest fire activity beginning around the mid-1980’s (see Figure 1 (a) and (c) in Westerling 2016), including more frequent large fires (> 1,000 acres), fires that burned longer, and longer wildfire seasons (Westerling et al 2006; Westerling 2016). Additionally, there is evidence that the number of very large fires (> ~12,400 acres) has also been increasing over the last 30 years, particularly across parts of the southeastern and southwestern U.S. (Barbero et al. 2014).

These observations square with another recent study (Jolly et al 2015), which showed that conditions have become more conducive to fire in many parts of the world. Researchers used historic climate data from 1979 to 2013 to calculate the length of the fire weather season over the last 35 years, based on several common fire danger indices used in the U.S., Canada, and Australia. They found that, globally, the length of the average fire weather season increased by almost 19% and the amount of land area affected by long fire weather seasons doubled. Their results coincided with evidence of recent trends in the U.S. For example, in 2012, about 47% of the vegetated area of the U.S. experienced a longer-than-normal fire weather season according to their estimates and that resulted in a “near-record setting ~3.8MHa [9.4 million acres] of burned area” (Jolly et al. 2015).

Although, even in the U.S., not all regions are experiencing more wildfire. The Northeast, for example, is known for some historic mega-fires, but now has an annual average area burned of only 0.04% of forest area and fire histories show a decline for the last 60 years in both the area burned and the size of fires (Irland 2013). This decline is likely due to better detection, regulation, and control methods since the 1950’s, but it also means more fuel has accumulated on the landscape (Irland 2013). Importantly, extreme fire behavior can still occur in regions with very infrequent fire and, in fact, almost every part of the Northeast has experienced extreme fire years or unusually large fires since that decline began in the 1950’s (Irland 2013).

A Climate Change Connection?

A number of factors have contributed to the recent increase in U.S. wildfires, including higher fuel loads from historic fire suppression and large-scale forest mortality due to bark beetle outbreaks, but an important question is: To what extent, if any, has climate change contributed to these observed trends? Evidence suggests it has played a role. The Intergovernmental Panel on Climate Change (IPCC) noted that climate change has already had a major impact on wildfire activity in North America, some parts of Europe (specifically Portugal and Greece), and Africa in recent years (IPCC AR5 SPM, Figure SPM.4). In fact, fire is one of the key climate change-related risks they list for North America and Europe and that risk is projected to increase as we move farther into this century (IPCC AR5 SPM, Figure SPM.8). The 2014 U.S. National Climate Assessment also identified a link between climate change and fire, noting that “Climate change is contributing to an increase in wildfires across the U.S. West.” They point specifically to hotter and drier weather and earlier snowmelt, which has increased the length of the fire season and amount of acreage burned (NCA 2014).

Numerous studies suggest changes in climate are largely responsible for observed wildfire trends in the U.S. (Littell et al. 2009; Jolly et al. 2015; Westerling et al. 2006; Westerling 2016; Attiwill & Binkley 2013) and there is evidence for this connection in both modeling and observational studies. For example, Barbero et al. (2014) developed models that successfully replicated historic fire patterns across the continental U.S. using ONLY climate variables, which indicates climate is the major mechanism driving fire activity. Another study found that climate was a significant driver of fire activity in the western U.S. from 1916 to 2003—explaining an average of 39% of the variability in area burned—and there was an even stronger linkage in the most recent decades from 1977 to 2003, where climate explained an average of 64% of the area burned (Littell et al. 2009). A third example, mentioned earlier, is research from Dennison et al. (2014) that found similar wildfire trends across a variety of western U.S. ecoregions with different vegetation types, fire seasons, fuel types, and fire frequencies (see Figure 2), but similar increases in severe drought. This suggests prevailing climatic conditions, rather than site-specific dynamics, are responsible. Evidence suggests climate change will only continue to play a bigger role in shaping fire trends, as we move from global fire regimes that were driven by precipitation during the pre-industrial period and by human ignition and suppression during the 18th century, into a new temperature-driven global fire regime (Pechony & Shindell 2010).

Climate & Fire: Take Homes for Forest Managers

Climate Drives Fire Activity

While there are many factors that determine where, when, and how wildfires burn, climate is well-recognized as one of the primary controls on fire activity (Dennison et al. 2014). At the simplest level, it influences the availability and flammability of fuels, but fire requires three components—biomass to burn, the right atmospheric conditions, and ignition—and climate affects all of these components “in complex ways and over multiple timescales” (Moritz et al. 2012). In the short-term, climate controls ignition and propagation, while in the long term it affects fuels by influencing primary productivity and vegetation (Urbieta et al. 2015).

Time scale Matters

The diagram in Figure 3 (below) outlines how different aspects of climate control fire at different scales. For example, in some North American regions, fire regimes are closely related to natural modes of climate variability, such as the El Niño Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and the Atlantic Multidecadal Oscillation (AMO) (Whitlock et al. 2010; Fauria & Johnson 2008)—see our previous bulletin on Global Temperature Trends for an explanation of how the ENSO/PDO system influences fire regimes worldwide. We are accustomed to thinking about the drivers of fire at shorter timescales (i.e. at the level of individual fires—seasonal-to-annual—and how they propagate—hourly-to-annual) because fire management and response systems typically operate at those scales, but the influence of decade-to-decade climate fluctuations and the long-term warming trend  are no less important. Changes in average climate, variability, and long-term trends can shift the fire regime in a given region and, since climate conditions are projected to continue changing for the foreseeable future, it is reasonable for forest managers to expect and prepare for deviations from the historic fire regime in their area.

Drought & Fire Risk

More immediate fire-climate impacts will most likely come through drought, which also played a role in the record-breaking 2015 U.S. fire season. Drought is projected to increase in both frequency and severity in many regions and it is known to directly affect fire severity, extent, and frequency (Littell et al. 2016). The uncertainty of future precipitation patterns, as discussed in an earlier bulletin, presents a challenge because there are very few regions of the world where we have confidence in predictions of future drought. That said, warmer temperatures alone can increase the intensity of individual drought events (and associated fire risk) by increasing potential evapotranspiration (as discussed previously)—a factor that has been implicated in the severity of the recent California drought (Diffenbaugh et al. 2015).

What’s Limiting: Fuel or Moisture?

The impact of climate change on fire activity will largely depend on whether an ecosystem tends to be more fuel-limited or climate-limited (Littell et al. 2009; Steel et al. 2015; Whitlock et al. 2010). In the former, fire is limited by the amount of fuel available and these are often drier, more sparsely vegetated areas that experience frequent, lower-severity wildfires. In contrast, fire in climate-limited systems is controlled by fuel flammability and these are generally more moist systems with significant biomass that experience infrequent, more severe wildfires. For example, more precipitation can actually increase fire risk in fuel-limited ecosystems by increasing the quantity of fine fuels (Dennison et al. 2014), compared to climate-limited ecosystems like the boreal forest where moisture rather than fuel accumulation is the primary determinant of fire behavior and more precipitation would typically decrease fire risk (Fauria & Johnson 2008). Factors like human intervention can flip a system from one end of the spectrum to another. For example, researchers studying 130 years of fire history in a Spanish province in the Mediterranean found that rural depopulation and farm abandonment increased fuels and shifted the fire regime in that region from fuel-limited to climate-limited, leading fire activity to become more drought-driven (Pausas & Fernandez-Munoz 2012). Fire activity in these climate-limited ecosystems is sensitive to changes in temperature, so warming may especially increase fire risk in these systems.

Coming up…

In Part II, we outline what the latest research suggests in terms of future fire frequency, extent, and/or severity and we discuss the changing context of more fire in the WUI, rising costs, and changing organizational structures, as well as providing useful resources for more information.

~            ~             ~             ~             ~


Attiwill, P., Binkley, D. 2013. Editorial: Exploring the mega-fire reality: A ‘Forest Ecology and Management’ conference. Forest Ecology and Management. 294: 1-3.

Barbero, R., Abatzoglou, J.T., Steel, E.A., Larkin, N.K. 2014. Modeling very large-fire occurrences over the continental United States from weather and climate forcing. Environ. Res. Lett. 9: 11pp.

Dennison, P.E., Brewer, S.C., Arnold, J.D., Moritz, M.A. 2014. Large wildfire trends in the western United States, 1984-2011. Geophys. Res. Lett. 41: 2928-2933.

Diffenbaugh, N.S. Swain, D.L., Touma, D. 2015. Anthropogenic warming has increased drought risk in California. PNAS. 112(13): 3931-3936.

Doerr, S.H. and Santín, C. 2016. Global trends in wildfire and its impacts: perceptions versus realities in a changing world. Phil. Trans. R. Soc. B. 371: 20150345.

Fauria, M.M. and Johnson, E.A. 2008. Climate and wildfires in the North American boreal forest. Phil. Trans. R. Soc. B. 363: 2317-2329.

Giglio, L., Randerson, J.T., van der Werf, G.R. 2013. Analysis of daily, monthly, and annual burned area using the fourth-generation global fire emissions database (GFED4). Journal of Geophysical Research: Biogeosciences. 118: 317-328.

IPCC, 2014: Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland, 151 pp.

Irland, L.C. 2013. Extreme value analysis of forest fires from New York to Nova Scotia, 1950-2010. Forest  Ecology and Management. 294: 150-157.

Jolly, W.M., Cochrane, M.A., Freeborn, P.H., Holden, Z.A., Brown, T.J., Williamson, G.J., Bowman, D.M.J.S. Climate-induced variations in global wildfire danger from 1979 to 2013. Nature Communications. 6: 7537. DOI: 10.1038/ncomms8537.

Littell, J.S., McKenzie, D., Peterson, D.L., Westerling, A.L. 2009. Climate and wildfire area burned in western U.S. ecoprovinces, 1916-2003. Ecological Applications. 19(4): 1003-1021.

Littell, J.S., Peterson, D.L., Riley, K.L., Liu, Y., Luce, C.H. 2016. A review of the relationships between drought and forest fire in the United States. Global Change Biology. 22: 2353-2369.

Melillo, Jerry M., Terese (T.C.) Richmond, and Gary W. Yohe, Eds., 2014: Climate Change Impacts in the United States: The Third National Climate Assessment. U.S. Global Change Research Program, 841 pp. doi:10.7930/J0Z31WJ2.

Moritz, M.A., Parisien, M-A., Batllori, E., Krawchuk, M.A., Van Dorn, J., Ganz, D.J., Hayhoe, K. 2012. Climate change and disruptions to global fire activity. Ecosphere. 3(6):49.

Pausas, J.G., Fernández-Muñoz, S. 2012. Fire regime changes in the Western Mediterranean Basin: from fuel-limited to drought-driven fire regime. Climatic Change. 110: 215-226.

Pechony, O., Shindell, D.T. 2010. Driving forces of global wildfires over the past millennium and the forthcoming century. PNAS. 107(45): 19167-19170.

Steel, Z.L., Safford, H.D., Viers, J.H. 2015. The fire frequency-severity relationship and the legacy of fire suppression in California forests. Ecosphere. 6(1): Article 8, 23pp.

Urbieta, I.R., Zavala, G., Bedia, J., Gutiérrez, J.M., San Miguel-Ayanz, J., Camia, A., Keeley, J.E., Moreno, J.M. 2015. Fire activity as a function of fire-weather seasonal severity and antecedent climate across spatial scales in southern Europe and Pacific western USA. Environ. Res. Lett. 10:114013.

Westerling, A.L. 2016. Increasing western US forest wildfire activity: sensitivity to changes in the timing of spring. Phil. Trans. R. Soc. B. 371: 20150178.

Westerling, A.L., Hidalgo, H.G., Cayan, D.R., Swetnam, T.W. 2006. Warming and Earlier Spring Increase Western U.S. Forest Wildfire Activity. Science. 313: 940-943.

Whitlock, C., Higuera, P.E., McWethy, D.B., Briles, C.E. 2010. Paleoecological Perspectives on Fire Ecology: Revisiting the Fire-Regime Concept. The Open Ecology Journal. 3: 6-23.

Resiliency Assessment Framework

(click here to download a pdf of this complete article)

By Eric Walberg


Optimizing forest management to account for the risks and opportunities posed by climate change is a challenge on many fronts. Limitations in the precision of climate models, uncertainties about natural system response, and the need to integrate climate concerns with other aspects of forest management are all complicating factors.

To better position CSLN members to respond to these risks and opportunities Manomet is proposing the development of a monitoring and management system that we are calling the Resiliency Assessment Framework (RAF). The RAF will track changing regional climate and forest conditions and allow CSLN members to evaluate conditions on their lands in light of the changing regional context. This approach is intended to support the inclusion of climate concerns in forest management plans by providing an opportunity to link management decision points to the data inputs from the RAF.

The RAF will be an optional component of the CSLN and will be intentionally structured to minimize additional work load and maximize utility in improving forest management. While many research questions associated with climate change and forest response might be addressed by this type of monitoring framework, our goal is a system that will maximize forest health and productivity.

Proposed Program Structure

The RAF will consist of three major components:

  • climate-science-center-regionsAssessment and Tracking of Changing Regional Context: Manomet will develop a synopsis of climate change and forest response trends and projections for each of the six regions associated with the U.S. Climate Science Centers.
  • Local Monitoring and Evaluation: Participating CSLN members will establish or augment an existing monitoring program to document changing forest conditions on the lands that they manage and support comparison of local and regional forest conditions.
  • Climate Component for Forest Management Plans: Participating CSLN members will develop a climate change component in their forest management plans that links to the monitoring data generated by the RAF.

The majority of the regional data will come from public sources and will be based on research that is already underway or just being started. The frequency and extent of data collection on local forest conditions will be at the discretion of participating CSLN members.

Initial Development, Testing and Evaluation in New England

Initial development of the RAF will take place as a pilot effort in New England over the next year. Manomet will begin the process by developing a regional trends and projections report for the Northeast region and by working with participating CSLN members with land holdings in New England to develop and test local monitoring protocols and draft climate components for forest management plans. Assuming that the pilot phase is successful, the RAF will be expanded region by region in following years.

Questions the RAF Will Address

The two overarching questions that the RAF is intended to address are:

  • How are climate conditions changing by region and site?
  • How are forest conditions changing in response?

Through the pilot phase of the project Manomet will work with CSLN members to develop a set of specific research questions. As previously stated, the intent is to strike a balance between level of effort and utility in improving forest management. Examples of the type of specific questions that might be posed include:

  • Is a warming climate increasing growth rates for particular tree species?
    • Possible regional climate metrics: change in length of growing season, change in average annual temperature, range of seasonal temperatures
    • Possible regional forest metrics: FIA forest growth rates by species
    • Possible local forest metrics: growth rates by species
  • How is the frequency and severity of drought changing and are there discernable forest impacts?
    • Possible regional climate metrics: PDSI (Palmer Drought Severity Index), SPI (Standardized Precipitation Index), soil moisture, VPD (Vapor Pressure Deficit)
    • Possible regional forest metrics: Remote sensing of forest health and mortality, FIA forest health metrics, FIA tree mortality data, canopy water content
    • Possible local forest metrics: tree crown condition, tree mortality
  • How is temperature variability changing and is there a discernable forest response?
    • Possible regional climate metrics: frequency of freeze/thaw events, range of seasonal temperatures, frequency of false springs
    • Possible regional forest metrics: Remote sensing of frost damage following leaf out, FIA forest health metrics, FIA forest growth rates
    • Possible local forest metrics: tree crown condition, growth rates
  • Are storm events changing in frequency and intensity and what is the forest response?
    • Possible regional climate metrics: maximum wind speed, frequency of threshold wind exceedance, persistence of storm systems
    • Possible regional forest metrics: FIA forest health metrics, FIA tree mortality data, wind throw
    • Possible local forest metrics: tree crown condition, wind throw

Obvious challenges exist in differentiating climate impacts from the many other factors that influence forest health and productivity. However, as climate change progresses it is likely that climate-related factors will become more prominent forest stressors and will therefore be more readily identifiable. For example, recent studies of the impact of “hot drought” on forests in the western U.S. have identified a climate change component in the excessive heat that has exacerbated tree mortality. The RAF can potentially serve as an early warning system and hopefully will provide insight on emerging factors in forest health and changing competitiveness of particular tree species.

Measures of Success

Key measures of success for the RAF include the following considerations:

  • Does implementation of the RAF result in forest management insight would not occur in its absence?
  • Is the RAF worth the investment of time and energy?
  • Does the RAF improve understanding of how climate change is impacting forests?
  • Does the RAF provide a mechanism for engagement and education on climate change?
  • Over the long term, does the RAF result in improved forest health and resiliency?

Once the pilot phase is underway it will be possible to identify more specific measures of success associated with specific research questions.

The next step in this process will be a survey of CSLN members to get a better idea of what you are currently doing in the way of forest monitoring and to take a first cut at identifying priority research questions. The survey results will be discussed at the October 26, 2016 CSLN member gathering in Boston.

Climate Change & Forest Productivity

(Click here to download a pdf version of this full article or a one-page synopsis)

By Jennifer Hushaw

Considerable attention has been paid to understanding how climate change may alter the abundance and distribution of tree species, as discussed in our previous bulletin on modeling future forests, but an equally important consideration is how climate change may alter productivity. Research suggests climate change has the potential to affect not just where, but how well our forests grow. This bulletin highlights recent work by researchers at Virginia Tech, University of Maine, the US Forest Service, and others that estimates how productivity may shift as a result of changing climate.

Productivity & Site Index

One measure of potential forest productivity is site index—defined as the average total height (in meters) that dominant and co-dominant trees attain at a specified base age in even-aged stands. Of course, this is based on the assumption that forests are even-aged and consist of a single species, which can be problematic in regions dominated by uneven-aged, mixed species stands, such as the eastern US. However, it is a commonly used metric that provides some utility. Researchers have responded to these known limitations by attempting to predict observed site index using site attributes like climate, topography, and soil characteristics.

Study Overview

In a recent study published in the Canadian Journal of Forest Research (Jiang et al. 2015), researchers created models to predict site index (base age 50) for 20 eastern tree species (as well as hardwoods and conifers generally*) based on 15 soil and 37 climate variables. The models successfully predicted current site index values observed through USFS Forest Inventory and Analysis (FIA) data, which provides confidence in their ability to accurately represent on-the-ground conditions. Then they were re-run with future, rather than contemporary, climate data to estimate how site index would change under projected future conditions.

They utilized vegetation and site index data from the FIA program, contemporary (1961 to 1990) and future (2030, 2060, and 2090) climate data from the USFS Rocky Mountain Research Station representing four different future emissions scenarios, and soils data from the USDA Soil Survey Geographic (SSURGO) database.

The models were developed using a statistical technique (Random Forests—a classification and regression tree analysis) that has been shown to be very adept at analyzing these types of research questions and datasets. With the analysis they employed, they were also able to calculate confidence intervals to determine if the predicted changes in site index were significant or not.


Researchers used all climate and soil variables (to ensure maximum predictive accuracy) to generate maps of site index change. They found that site index may increase or decrease in the future, depending on the species and the geographic region in question. Site index models were generated for individual species, as well as two broad species groups (hardwood and conifer), but only the species-group results were reported.

Key Findings

Current site index:
  • There was more variation in observed site index for conifers than hardwoods across the eastern US.
  • The models that performed best at predicting site index included BOTH climate and soils data.
  • Models that used only climate data to predict site index performed better than those using soils alone.
  • Variables that were useful for predicting site index included:
    • Soil pH
    • Effective soil depth (especially for conifers)
    • Total available soil water capacity
    • Ratio of summer precipitation to total precipitation
    • Summer-winter temperature differential
    • Growing-season precipitation (April—September)
  • For conifers, current site index showed a pattern of increasing from north to south.
  • For hardwoods, current site index showed a pattern of increasing from north and west to southeast.
Future Site Index:
  • For conifers, there was a significant increase in average site index (+0.5 – +2.4m) over the 21st
  • For hardwoods, there was a significant decrease in average site index (up to -1.7m) over the 21st
  • Several regions showed contrasting results depending on the climate change scenario.
  • Variables that were important for determining future changes in site index were related to:
    • The ratio of growing-degree-days to summer precipitation
    • The start and length of the frost-free season
    • Average and accumulated growing-season temperatures
    • Changes in moisture index or summer temperatures in combination with changes in midwinter ambient temperatures
  • Under the lowest emissions scenario, more FIA plots showed a significant increase in site index and fewer showed a significant decrease, whereas the higher emissions scenarios consistently showed the opposite result—suggesting that there may be some overall benefit for forest productivity under moderate warming that disappears under higher levels of warming.


This study is an example of the research being done to better understand how changing climate conditions will alter forest productivity. A key take-home is how different the forest response can be depending on the rate and level of warming, which is also a key area of uncertainty. This highlights the important ramifications of different climate trajectories and suggests that forest managers may want to keep their eye on those trends over time. In some cases, it may be beneficial to shift the species mix toward those projected to experience an increase in site index. However, these results should also be considered in conjunction with other research related to potential productivity changes, such as growth increases due to CO2 fertilization or decreases due to extreme heat events. We will continue to monitor new and emerging research on this topic going forward.


Note: For those interested in a similar analysis for western US tree species, please see a paper by Weiskittel et al (2011) entitled Linking climate, gross primary productivity, and site index across forests of the western United States.

* Species comprising the hardwood and conifer species groups in this analysis:

Hardwood Conifer
White oak Loblolly Pine
Yellow poplar Shortleaf Pine
Quaking aspen Eastern white pine
Northern red oak Balsam fir
Sugar maple Red pine
Red maple Slash pine
Black oak Black spruce
White ash Tamarack (native)
Green ash N. white cedar
Sweetgum Virginia pine


~            ~             ~             ~             ~



Jiang, H., Radtke, P.J., Weiskittel, A.R., Coulston, J.W., Guertin, P.J. 2015. Climate- and soil-based models of site productivity in eastern US tree species. Can. J. For. Res. 45: 325-342.

Weiskittel, A.R., Crookston, N.L., Radtke, P.J. 2011. Linking climate, gross primary productivity, and site index across forests of the western United States. Can. J. For. Res. 41: 1710-1721.



Carbon Markets and Forests: What Does the Future Hold?

(click here to download a pdf of this complete article)

By Eric Walberg


Global efforts to reduce carbon emissions are ramping up and carbon markets will play an increasingly important role in limiting warming to the 2 degree C ceiling established by the Paris Climate Agreement.  I participated in the largest annual North American carbon market conference in San Diego, CA, May 4-6, 2016. The California Cap and Trade system formed the backdrop for many of the sessions, but the conference drew international participants and presentations covered a range of global topics. Recurrent themes included the impact of the Paris Climate Accord, the future of the California carbon market, linkages between the California Cap and Trade system and other sub-national programs, the future of the Clean Power Plan, and possible inclusion of Reducing Emissions from Deforestation and Forest Degradation (REDD) projects in the California market.

What are the opportunities and ramifications for the forestry sector? What role will forests play in meeting the national commitments associated with the Paris agreement? This month’s bulletin is an exploration of those questions as informed by the presentations and discussions at the conference.

Key Themes from the Conference


The ramifications of the December 2015 Paris Climate Agreement were discussed in several of the sessions. The general consensus is that the Agreement sends a positive signal for global expansion of carbon pricing, regulations, compliance markets, and voluntary markets in efforts to limit warming to the 2 degree C goal. The Paris Agreement establishes a bare bones framework for the creation of new international carbon markets and cooperative approaches to reducing greenhouse gas emissions.  The high-level framing in Article 6 of the Agreement (see hyperlink pg. 23) must be fleshed out before the nature of the resulting markets and cooperative agreements becomes clear.  It is too early to know what opportunities for the forestry sector might result.

A related topic in these discussions was the tremendous need for additional capital to finance the conversion to a green economy. Additional regulation and/or establishment of a price on carbon were two methods discussed to drive capital towards needed solutions. Green bonds are also seen as a growth area with some early indications of investor preference for green bonds driving higher prices in the secondary market.  China is poised to have a major impact as they establish a national cap and trade system in 2017 and become a major issuer of green bonds. Market commentators estimate that China’s green bond market could be worth $230 billion in the next five years.


The California Cap and Trade system appears to have addressed many of the fundamental flaws of earlier systems. A price floor in the offset market has created demand and stability. Rigorous project review on the part of the California Air Resources Board has created investor confidence, but has also created significant hurdles for offset project developers. Thus far, the bulk of the emission reductions in California have been driven by actions within capped sectors (to reduce emissions), rather than through purchase of offset credits from non-capped sectors such as forestry. The California system continues to function as a laboratory of innovation and will influence international efforts to fulfill the Paris Agreement.

The initial enabling legislation (AB32) established the program through 2020 and efforts to extend the cap and trade framework are underway in the California legislature. The general sense from the conference discussions is that that program will be extended, but will likely be modified in the process. The program also faces a lawsuit by the California Chamber of Commerce (CCC). A state judge rejected the assertion by the CCC that the program is an illegal tax, but an appeal is pending.


Forest offset projects account for the majority of offset projects approved in the California Cap and Trade system so far. Three categories of forest offset projects are possible: (1) afforestation, (2) avoided conversion, and (3) improved forest management. Thus far, the majority of the approved projects are in the improved forest management category. Several sessions touched on the notion of “charismatic” carbon credits—projects that bring co-benefits such as flood control and water quality protection. It is not clear if this is a factor in the prevalence of forest offset projects in the compliance market.

One of the sessions included an in-depth discussion of areas of risk associated with forest offset projects and how parties attempt to allocate that risk in contract negotiations. The five areas of risk were: (1) the possibility of credit invalidation, (2) failure to deliver a successful project, (3) reversal of a project, (4) land restrictions associated with projects, and (5) price*.

  • Invalidation of a project is a risk during the first eight years of a project and could result from a material misstatement (greater than 5%) of the carbon sequestration value of a project, failure to comply with all relevant environmental, health and safety laws, or double dipping (selling the same offsets into multiple programs).
  • Project delivery failure could be associated with multiple causes such as insolvency, failure to meet statutory deadlines, negligence, etc.
  • Reversal could be due to unintentional causes such as fire or wind storm, or intentional causes such as negligence or willful intent. In the event of an unintentional reversal the credits are covered by a buffer pool maintained by the California Air Resources Board. In the case of intentional reversal the owner is responsible for replacing the credits.
  • Land restrictions are primarily to meet the carbon sequestration goals associated with the contract. Harvesting is permitted as long as carbon sequestration goals are met. The land can be transferred but subsequent owners must assume all carbon responsibilities. A second category of land restrictions are those associated with compliance with the previously mentioned environmental, health and safety laws.
  • Price concerns include both the market value of the credits and the contractual allocation of risk and financial reward among all of the parties involved in assembling an offset project.

*Source: From a presentation entitled: “The Art of the Deal: Legal Considerations with Carbon Projects” by Erika Anderson of Anderson Law on May 4, 2016 at the Navigating the American Carbon World conference in San Diego, California.


The California Cap and Trade system is a hub for a growing network of sub-national entities that are linking their markets. The Western Climate Initiative (WCI) was launched in 2007 to evaluate and implement policies to tackle climate change. Membership of the WCI includes California, Washington, Oregon, Arizona, New Mexico, Montana, Utah, British Columbia, Manitoba, Ontario, and Québec. Building on the WCI, California and Québec completed an agreement in 2013 linking their programs. Ontario has indicated that they will be next to link their program.

In a parallel effort, California began engaging on REDD through the creation of the Governors’ Climate and Forest Task Force in 2008. This subnational government initiative is a network and forum focused on forest conservation, climate mitigation, and exploring linkage between REDD programs and the California Cap and Trade system. This process resulted in development of a 2010 Memorandum of Understanding between California, Acre, Brazil, and Chiapas, Mexico to assess the details associated with program linkage. Technical and policy recommendations were developed by a team of experts and delivered to all three of the partners in 2013. It is not yet clear when this process might result in formal linkage of REDD projects with the California market or exactly what form that linkage would take.

Challenges and Opportunities for the Forestry Sector

As signatory nations strive to meet the emission reduction goals associated with the Paris Agreement it is certain that afforestation, forest protection, and enhanced forest management will be key features of national programs. Given the prominent role that forest offset projects play in the California Cap and Trade system it is reasonable to assume that forest offsets will be included in other markets. Regulatory change and/or establishment of a price on carbon will likely increase the value of the climate regulation services provided by forests. The following are my thoughts on the challenges and opportunities for the forestry sector based on the conference discussions.

  • Participation in the California offset market: Barring a successful legal challenge to the program or significant regulatory change, the opportunity for forest offset projects in the California market will continue to be the most tangible and immediate opportunity for the forestry sector in the compliance market. Opportunities for offset projects will continue to exist in the voluntary market, but it is not likely that prices will rival those offered in the compliance market.
  • REDD offset market: Early indications are that, if and when REDD projects enter the California market, the only project categories that will be approved are afforestation and reforestation. It is possible that enhanced forest management projects will eventually be included pending a successful pilot period with afforestation and reforestation projects.
  • Possible inclusion of biomass energy and/or forest offsets in programs that develop in response to the Clean Power Plan: Given the legal challenges to the CPP it is difficult to know if the draft regulatory language will survive intact. If the existing framework does move forward it appears that the use of biomass energy will be available to states as one element of transition to renewable energy portfolios. The details of the carbon accounting and economics associated with biomass under the CPP are not known at this point. It does not appear likely that forest offset projects will be accepted by EPA as a substitute for reducing emissions from existing power generation facilities, but it is possible that carbon markets that develop in response to the CPP could include forest offsets in a broader context.
  • Regional Greenhouse Gas Initiative (RGGI) forest offsets: A 2014 reduction in the RGGI emissions cap by 45% resulted in renewed interest in the market and allowance prices have increased from $2.80 in March of 2013 to $7.05 in December of 2015, with a drop to $5.25 in March of 2016. These prices have not been high enough to foster demand for offset projects but that could change in the future if allowance prices rise.
  • Competitive advantage for wood building materials: Regulatory change and carbon pricing will likely increase the expense of competing materials with a larger carbon footprint, such as concrete and steel.
  • Increased efforts to reduce deforestation in the tropics: These efforts may reduce opportunities for commercial forestry operations in the tropics and could result in increased demand for forest products from temperate zones.
  • REDD and related projects: New commercial opportunities may emerge for sustainable forestry and agroforestry as a component of REDD projects and other efforts to comply with the Paris Agreement.

Manomet will continue to monitor developments in the policy realm and carbon markets and will report back to Climate Smart Land Network members on an as needed basis.

Modeling Future Forests

(click here to download a pdf of the full article or a one-page synopsis)

By Jennifer Hushaw

Understanding how forests responded to past changes in the Earth’s climate has been a long-standing area of research, but in recent years there has also been growing interest in anticipating how modern climate change may lead to shifts in tree species abundance and distribution. Of course, climate is just one of many factors that determine why trees grow where they grow, including soils, competition, land-use history, and synergistic relationships with other species, e.g. seed dispersers. Partly as a result of this complexity, there is a lot of uncertainty in the results of vegetation models that estimate future habitat suitability or distribution of tree species.

Two things we can say for sure are that (1) tree species will respond independently to changing conditions, so we may see novel species associations and forest types in some locations in the future and (2) there will be significant time lags in forest response (see box, right).

In this bulletin, we briefly review several modeling efforts and how they compare, as well as highlighting potential limitations and best practices for utilizing the results.

Vegetation Models: An Overview

The vegetation models used to assess potential tree species shifts can be broadly sorted into two categories on either end of a spectrum, from empirical (i.e. statistical) to process-based (i.e. mechanistic) models.

Empirical models quantify statistical relationships between species occurrence data, such as plot data from the US Forest Service Forest Inventory and Analysis (FIA), and relevant environmental variables, such as soils and climate, then use those correlations to project into the future. These are often referred to as species distribution models, niche models or bioclimatic envelope models.

Example: DISTRIB, the core model used in development of the Climate Change Tree Atlas (see table below), uses a statistical approach known as regression tree analysis to define the ecological niche of a species based on (1) a series of climate, soil, elevation, and landuse predictor variables and (2) data from FIA about the relative abundance of a species in the overstory. More specifically, it utilizes a relatively new ensemble data-mining technique called Random Forests, which has some improvements that are designed to avoid “overfitting” the data. For more detail on the technique read this paper by Prasad et al 2006. Based on these results, the model has been used to map where the habitat (in terms of climate conditions, soil characteristics, etc.) is suitable for a particular species now and in the year 2100. This tells us something about how likely a species is to persist in particular area.

Note: In the future, the Climate Change Tree Atlas will use DISTRIB in conjunction with a simulation model called SHIFT to go beyond predictions of future suitable habitat and estimate actual species movement in terms of the likelihood of colonization.

Process-based models are generally more complex because they simulate the actual underlying processes, such as disturbance, growth, and regeneration. Forest gap models, ecosystem models, forest landscape models, and dynamic global vegetation models (DGVMs) fall under this category.

Example: LANDIS PRO is a spatially explicit forest landscape model that simulates processes at the species- (e.g. growth, seedling establishment, mortality), stand- (e.g. competition, stand development), and landscape-scale (e.g. disturbance from fire, insects, harvest, etc.). By “growing” the forests in this way, LANDIS can be used to compare species in the future under a climate change and no climate change scenario. This tells us something about how likely a species is to become established in a particular area.

These categories are not mutually exclusive and there are an increasing number of hybrid approaches used in research. Nor is one approach necessarily better than another—each has its strengths and weaknesses depending on scale, data availability, and the particular research question. A helpful summary of key differences is below:

For more detailed information on this topic, we recommend visiting the Landscape Analysis section of the US Forest Service Climate Change Resource Center website.

Table 1 in this paper by Littell et al (2011) also has a useful comparison of the strengths and weaknesses of different types of empirical and process models, for reference.

Model Comparison

The table below compares several modeling efforts that estimate changes in habitat suitability or distribution for U.S. tree species under future climate change. Model names are hyperlinks that take you to the project website where you can view results, including maps (in some cases), for different species. This table is intended to help forest managers quickly navigate to existing projections of species shift and weigh the merits and characteristics of each approach.

Comparing the results from different models reveals whether they generally agree (lending greater confidence) or disagree on the outlook for particular species. Some of this work is being carried out by the US Forest Service through their on-going series of Vulnerability Assessments (see final row in the table below) and the CSLN will alert Network members to similar comparative efforts as they arise.

Best Practices

Models incorporate imperfect information and are a simplified version of reality, but by understanding these imperfections, we can use models to decrease the uncertainty associated with the future.” ~ Littell et al 2011

  • Remember there will be significant time lags.
  • Consider projections for individual species, rather than forest types.
  • Use models to help reduce uncertainty about the future by identifying potential surprises and vulnerabilities1, potential magnitude of effects, and insight into mechanisms.2
  • Use more than one type of model (wherever possible) to assess likely vegetation shifts1—we can have greater confidence where different models agree.
  • Understand the assumptions in a given model and the implications of those assumptions.1
  • Use MODFACs, a decision support framework that scores adaptability for different tree species, in conjunction with models to determine whether a species is likely to fare better or worse than modeled projections.
  • Mistake maps of habitat suitability for depictions of where a tree species will actually be growing at that point in the future.
  • Use model projections as exact predictions of what will happen with future forest shifts.

1 Littell et al 2011    2 Kerns & Peterson 2014

Click the image to open a pdf of the model comparison table (with live hyperlinks):



Underestimating Adaptability

As we noted in a previous bulletin, there are some limitations associated with modeling efforts that rely on statistical relationships between environmental variables and current species distributions derived from FIA data (i.e. the realized niche), since that represents only a portion of the possible conditions under which a species could grow (i.e. the fundamental niche). Revisit part of our July 2015 bulletin on uncertainty and forest response for a brief explanation of how the absence of data on the fundamental niche can lead to underestimating the potential adaptability of some tree species. This is not to say that forests aren’t vulnerable in other ways, such as increasing damage from exotic pests and extreme weather, but they may be more adaptable in terms of temperature tolerance than some results suggest.

Take-Home Message

As an initial step, we recommend CSLN members spend a little time perusing the results of the modeling efforts listed above, to get a sense for the general outlook for species that dominate their economic or management concerns. Noting where (and if) the models agree can highlight potential areas of vulnerability (or opportunity) to be explored further. Members who have an interest in digging-in on projections for a particular species, can contact the CSLN staff for additional assistance.

All the modeling efforts agree on at least one thing—conditions are going to change. Most tree species will begin to experience novel climate conditions in some portion of their range and, in some cases, that may lead to local extirpation. Ultimately, the uncertainty is in knowing exactly where and when these species distribution shifts will happen. Generally, we expect species range expansion at the leading edge, in northern and higher elevations, and range contraction at the trailing edge, in southern and low-altitudinal limits. In particular, look for initial forest composition changes at range margins because it is regeneration success or failure there that will determine whether a species persists or migrates.


~            ~             ~             ~             ~


Adams, H.D., Williams, A.P., Chonggang, X., Rauscher, S.A., Jiang, X., McDowell, N.G. 2013. Empirical and process-based approaches to climate-induced forest mortality models. Frontiers in Plant Science. 4 (438):5pp.

Iverson, L.; McKenzie, D. (February, 2014). Climate Change and Species Distribution. U.S. Department of Agriculture, Forest Service, Climate Change Resource Center. www.fs.usda.gov/ccrc/topics/species-distribution

Kerns, B.; Peterson, D.W. (May, 2014). An Overview of Vegetation Models for Climate Change Impacts. U.S. Department of Agriculture, Forest Service, Climate Change Resource Center. www.fs.usda.gov/ccrc/topics/overview-vegetation-models

Littell, J.S., McKenzie, D., Kerns, B.K., Cushman, S., Shaw, C.G. 2011. Managing uncertainty in climate-driven ecological models to inform adaptation to climate change. Ecosphere. 2(9): 102.

Loarie, S.R., Duffy, P.B., Hamilton, H., Asner, G.P., Field, C.B., Ackerly, D.D. 2009. The velocity of climate change. Nature. 462:1052-1055.

Pearson, R.G. 2006. Climate change and the migration capacity of species. Trends in Ecology and Evolution. 21(3):111-113.


Climate Change & Wildlife Impacts: Part 2

(click to download formatted pdfs of this full article or a one-page synopsis)

By Jennifer Hushaw, Si Balch, and Eric Walberg

In Part I of this bulletin, we described how climate change may soon rival human influence as the biggest driver of biodiversity change, and in this piece we look more closely at the links between climate and the habitat requirements of some specific groups of wildlife and game species in North America.

We don’t have much knowledge about exactly how climate will affect wildlife, even when compared to the uncertainties of forest response to climate change (as discussed previously). This is because wildlife species are higher up the trophic chain, with complicated interactions that determine their health and geographic limits (e.g. predator-prey relationships). In contrast, the distribution of vegetation communities is linked directly to climatic drivers and a short list of other factors, such as soils. The key to anticipating potential impacts is to understand the habitat characteristics that allow a species to survive in a particular place and determine how climate change might influence those conditions. The most robust predictions will be cases where a species has life history traits that are known to be particularly climate sensitive, such as the snowshoes hare’s reliance on snow cover for camouflage.

Wildlife species are far more mobile than plants and will therefore be able to respond quickly to changing climate conditions—changes in the behavior, distribution, or population of wildlife species are early indicators of climate change in the field. Quick response times will also make it easier for managers to adjust their management strategies and adapt based on results that are observable within a decade or so, rather than the multiple decades, or longer, needed to observe shifts in vegetation.

The impacts of climate change are not always direct—climate can and will affect species in less obvious ways through shifting habitat suitability, changes in prey availability or abundance, altered patterns of herbivory, and others. These indirect impacts can pose a major risk to wildlife when they exacerbate existing stressors. Any effort on the part of forest owners or managers to maintain, improve, or increase habitat for climatically-vulnerable species will help buffer against shifts in desired wildlife.

Species Highlights

Studies examining the impacts of climate change on specific wildlife species are still a relatively new realm of science and, while there is an incredible amount of research being done, the information available varies greatly depending on the species—as shown in the relative length of the sections below. The management recommendations included here are also general in nature, reflecting the fact that many of the standard wildlife management techniques we already employ are suitable for responding to the impacts of climate change for number of species.

Deer, Moose, Elk

Climate change will affect the population dynamics, range limits, habitat selection, browsing/foraging behavior, and disease outbreaks of these ungulate species.

As conditions change, moose and deer may alter their habitat selection, shifting where and when they utilize certain types of habitat. For example, decreases in lake ice in Michigan have led to more lake effect snow that creates harsh winter conditions for deer and increases their reliance on shelter in conifer swamps (although this increased precipitation is expected to shift more toward rain over the next century) (Hoving & Notaro 2015). White-tailed deer are not expected to decline as a direct result of climate change, but these types of changes in migration patterns and seasonal habitat are likely (Hoving et al 2013). Similarly, it has been documented that moose will change their behavior to alleviate heat stress, by moving to areas of higher and denser forest canopy when they reach a daytime temperature threshold of around 68⁰F (Melin et al 2014; Street et al 2015; NWF 2013a).

Range limits will also shift, and in some cases they already have, e.g. white-tailed deer have expanded into western boreal forests and climate has been shown to be an important factor determining their presence in that region (Dawe et al 2014). At the northern edge of their range, white-tailed deer are controlled by low winter temperatures and snow depth, so conifer stand deer yards are important for their survival because they provide thermal cover and reduced snow depth. As the climate changes, this cold/snow limiting line will move and two things are likely to result: (1) the more southerly deer yards will become less critical to survival and (2) deer populations will increase. Similarly, research on moose in China has revealed that climate is an important factor influencing population dynamics there; increases in late spring temperatures, in particular, have the potential to shift the southern limits of moose distribution northward (Dou et al 2013).

Changes in moose and deer population dynamics have been linked to large-scale climate patterns, particularly the North Atlantic Oscillation (NAO), which determines much of the snowfall and winter temperatures in northern latitudes (Post & Stenseth 1998). Likewise, recent research suggests that warmer temperatures and a shorter period of high quality forage in spring have led to nutritional deficiencies in maternal moose that decreased recruitment in the southern part of their range (Monteith et al 2015). As cold-adapted species, moose are generally considered to be highly vulnerable to climate change and decreases in abundance are likely by the middle of the century (Hoving et al 2013).

Climate change-induced decreases in snowpack have also led to shifts in browsing or foraging behavior in both moose and elk. In the case of moose, low snow conditions can increase browse on balsam fir compared to sugar maple or Viburnum (Christensen et al 2014). For elk, less snowpack means easier access to aspen shoots, which has caused substantial declines in aspen recruitment, particularly in the Rocky Mountains (Brodie et al 2012). In fact, climate change may actually provide some positive benefits for elk in the form of milder winters and better forage (NWF 2013a). Importantly, these kinds of climate-driven changes in plant-herbivore interactions can have wide reaching affects within the larger ecological community (Auer & Martin 2012).

Lastly, as discussed in Part I, climate change is altering pest and disease dynamics, including the transmission of wildlife diseases. White-tailed deer are vulnerable to hemorrhagic disease (HD), including epizootic hemorrhagic disease and bluetongue viruses, which are transmitted by biting midges. The first fall frost usually kills the insects, but longer summers will mean longer exposure times and hot, dry weather (which is likely to increase) has been strongly associated with past outbreaks, which suggests that the risk of widespread deer mortality from these diseases will increase (Hoving et al 2013; NWF 2013a). In recent years, warmer, shorter winters have also spelled trouble for moose populations, as winter ticks have proliferated enough to cause a significant increase in moose mortality (heavy infestations leave moose weak, vulnerable to disease, and at risk of cold exposure and death in cases where they rub off their insulating hair in an attempt to rid themselves of the ticks) (NWF 2013a).

Management Considerations:

  • Monitor for changing browsing patterns.
  • Provide areas of high, dense forest canopy for moose, particularly in southern parts of their range.
  • Factor increased deer browsing into regeneration planning.


Canada Lynx

Climate change will affect the population dynamics, distribution and abundance of prey species, hunting success, connectivity with peripheral populations, and range margins of lynx populations.

Canada Lynx is a charismatic animal that has drawn a great deal of conservation interest since its listing as a threatened species under the Endangered Species Act in March of 2000. It is considered highly vulnerable to climate change because it is a cold-adapted species that is particularly well-suited to hunting in deep snow, which gives it a competitive advantage over other predators (an advantage that will be lost with decreasing snow cover).

The decrease in snow cover will not only affect hunting success, but will also affect the distribution and abundance of the primary prey species, the snowshoe hare, whose populations are expected to shift northward due to climate change (Murray et al 2008). This is partly because hares in southern locations (with decreasing snow cover) often find themselves mismatched with their surroundings when they molt into their white winter coat in the absence of snow, which makes them far more visible to predators, with weekly survival decreases up to 7% (Zimova et al 2016). In contrast, the range of snowshoe hares has expanded in some northern locations, particularly Arctic Alaska, where warming temperatures and expanded shrub habitat have created more suitable conditions (Tape et al 2015).

Along with prey species abundance, climate itself is an important determinant of lynx population dynamics. Large-scale climate patterns, including the North Atlantic Oscillation index (NAO), the Southern Oscillation Index (SOI), and northern hemispheric temperature, play a role in producing and modifying the classic 10-year population cycles associated with lynx and snowshoe hare in the boreal parts of their range, by influencing rain and snowfall patterns (Yan et al 2013).

Climate change is also affecting connectivity between core and peripheral lynx populations, especially island populations that are sustained by immigration of individuals from other areas. Individuals from the core of the lynx range migrate over frozen rivers to reach island habitats, so warming conditions and less frequent formation of ice bridges will leave these populations even more isolated (Koen et al 2015; Licht et al 2015). As a result, range margin shifts are expected (and in some cases already observed) that include contraction of these smaller, peripheral groups, as well as northward contraction of the southern range boundary and the core population areas (Carroll 2007; Koen et al 2014).

Management Considerations:

  • Provide large, contiguous tracts of landscape, especially where there is connectivity with more stable Canadian populations of lynx.
  • Maintain patches of young, dense conifers for hare habitat.



Climate change may affect bat population distributions, reproductive success, hibernation behavior, and access to food.

Climate is known to influence the biogeography of bats, as well as their access to food, timing of hibernation, development, and other factors, so it is likely that changing climate conditions may adversely impact some bat species—some specific life history characteristics that may put bats at risk from climate change include (Sherwin et al 2012):

  • Small range size,
  • high latitude or high altitude range,
  • range that is likely to become water stressed,
  • fruit-based diet,
  • restricted to aerial hawking (prey pursued and caught in flight),
  • and restricted dispersal behavior.

Throughout the globe, there have been a number of documented cases of shifting bat populations linked to climate change, including range expansion of at least one Mediterranean species (Ancillotto et al 2016) and mostly northward shifts in a number of species in China (Wu 2016). In the Czech Republic, evidence suggests that a temperate, insectivorous bat is benefiting from rising spring temperatures, but the effect may be buffered by excessive summer rain that decreases reproductive success (Lučan et al 2013)—an example of the complicated nature of predicting exactly how climate change will impact a given wildlife species.

Of course, climate change is not the most immediate concern in the United States, where the introduction of white-nose syndrome to the eastern U.S. in the early 2000’s led to a massive decline in bat populations. However, changing climate conditions do have the potential to further stress these decimated populations, which is a cause for concern. This also highlights the need to protect the genetic diversity within refugial populations, especially on the leading edge for northward migration (Razgour et al 2013).

One particularly hard hit species, the Northern Long-eared Bat (NLB), was listed as threatened under the Endangered Species Act (ESA) and a final rule was released in January 2016 detailing the protections for this species under the ESA. Use these links to access a range map for the NLB and up-to-date maps of documented cases of white-nose syndrome, as well as details about the Final 4(d) Rule for the NLB under the ESA—there are some considerations for forest managers.

Management Considerations:

  • Leave a ¼ mile buffer around known hibernaculum*.
  • Leave a 150ft buffer around documented or potential maternal roosting trees*, especially during the pupping season in June & July.

* Contact your state agency or US Fish & Wildlife Service for more information about hibernaculum and maternal roost tree locations.


Forest Song Birds

Climate change will alter migration patterns, population dynamics, and the quality and availability of habitat for forest song birds.

Song bird species have exhibited a variety of responses to recent climate change. In particular, shifts in timing have been observed for some migratory species, including spring arrival shifted several days to more than a week early (depending on the species), such as Baltimore Oriole, Eastern Towhee, Red-eyed Vireo, Ruby-throated Hummingbird, and Mountain Bluebirds (NWF 2013b; Manomet). There is mixed evidence regarding changes in fall migration, with both early and late shifts observed in migrants passing through Massachusetts (Ellwood et al 2015).

Birds have the advantage of being able to respond rapidly to warming temperatures, but their ability to adapt depends on where they overwinter, how they receive their migration cues, and the level of mismatch between migration timing and the availability of associated food sources. In fact, evidence from 33 years of bird capture data collected by Manomet’s land bird conservation program suggests that short-distance migrants respond to temperature changes, while some mid-distance migrants respond to temperature and/or changes in the Southern Oscillation Index, and long-distance migrants tend not to change over time (Miller-Rushing et al 2008).

The vulnerability of individual species is also related to their specific habitat requirements and whether climate change may alter the availability of quality breeding or foraging areas. For example, a study of over 160 bird species in the Sierra Nevada mountains of California found that those associated with alpine/subalpine and aquatic habitats ranked as the most vulnerable, while those associated with drier habitats (i.e. foothill, sagebrush, and chaparral associated species) may experience range expansion in the future (Siegel et al 2014). Challenges may also arise for bird species that rely on temperature-sensitive prey species for food, such as aerial insectivores (e.g. Common Nighthawk, Chimney Swift, and Bank Swallow) that eat flying insects.

Lastly, as we have seen for other groups of species, rapid shifts in the distribution of wild birds will have implications for the spread and abundance of wildlife diseases (Van Hemert et al 2014).

Management Considerations:

Note: Visit the Climate Change Bird Atlas from the U.S. Forest Service for maps of projected change in species distribution for 147 birds in the eastern U.S.


Game Birds (Grouse, Turkey, Quail)

Climate change may affect habitat suitability and availability for important game bird species, as well as their breeding success and population dynamics—positive and negative projections vary from species to species.

Climate plays a role in the distribution of game bird species, as it does with many others. In fact, the population dynamics of several gamebirds seem to be influenced by large-scale climatic patterns (Kozma et al 2016; Williford et al 2016; Lusk et al 2001), but the effects of climate change are expected to vary significantly from one species to the next. For example, Black Grouse in Finland have experienced population declines for four decades related to seasonally asymmetric climate change. In particular, springs have warmed faster than the early summer period, so grouse lay their eggs earlier and then experience higher chick mortality when they hatch before temperatures are sufficiently warm (Ludwig et al 2006). Similarly, Spruce Grouse is considered moderately vulnerable because its montane spruce-fir habitat is rare (and likely to decline) in the southern edges of its boreal range. On the other hand, Ruffed Grouse is a resident species in the northeast U.S. whose range is projected to decrease and shift further north, even as overall populations remain relatively stable (Rodenhouse et al 2008; Hoving et al 2013).

In contrast, some gamebirds are likely to fare even better under climate change, including Wild Turkey (which has expanded northward (Niedzielski & Bowman 2015) and will benefit from less severe winters (Hoving et al 2013)), Northern bobwhite (which is likely to increase (Hoving et al 2013)), and Sage Grouse (which studies suggest may enjoy an increase in suitable habitat in some regions, such as southeastern Oregon, by the end of the century (Creutzburg et al 2015)).

Management Considerations:



Climate change has already led to increased temperatures in freshwater systems, putting cold-water fish species at risk of physiological stress or extirpation in certain waterways, while some warm-water species may experience increased growth rates and northward expansion.

Climate change has the potential for significant adverse impacts on cold-water fish species such as brook and rainbow trout. These species depend on access to cold water for reproduction and may also suffer from an increase in summer low flow stream conditions. As discussed in the August 2014 Bulletin, designing stream crossings to accommodate floods associated with the increase in heavy precipitation also has the benefit of minimizing fragmentation of aquatic habitat. Intact stream systems allow fish and other aquatic species to move in search of appropriate temperature and flow regimes.

For warm-water fish, evidence suggests that some species, such as small mouth bass, may experience increased growth rates as temperatures rise (although this growth effect may taper off if conditions become too warm later in the century) (Pease & Paukert n.d.). Some warm-water fishes have also moved northwards and are likely to continue expanding into freshwater systems traditionally dominated by cold-water species (Groffman et al 2014).

Management Considerations:

  • Upsize culverts, transition to arched structures, or use removable crossings to provide the win/win of reduced infrastructure damage from floods and enhanced connectivity of aquatic habitat.



Climate change will drive changes in habitat availability and suitability for amphibian species, which are highly sensitive to changes in temperature and precipitation.

There is weak evidence that climate change is driving observed declines in amphibian populations in various locations worldwide (Li et al 2013), but a number of studies suggest that future climate change is likely to lead to declines and/or range contractions (Barrett et al 2014; Loyola et al 2014; Wright et al 2015). These changes will be driven by a reduction in climatically suitable habitat, reduced soil moisture (which will reduce prey abundance and lead to loss of habitat), reduced snowfall and increased summer evaporation (which will change the duration and occurrence of seasonal wetlands) (Corn 2005).

Amphibians are particularly vulnerable to changing climate because their ectothermic physiology makes them very sensitive to temperature and precipitation changes, they have low dispersal capability, and often have strong associations with temporary wetlands that are likely to be threatened by climate change (Tuberville et al 2015).

Management Considerations:

  • Maintain appropriate buffer areas around water bodies, vernal pools, ephemeral and intermittent streams that act as amphibian habitat.


~            ~             ~             ~             ~


Ancillotto, L., Santini, L., Ranc, N., Maiorano, L., Russo, D. 2016. Extraordinary range expansion in a common bat: the potential roles of climate change and urbanization. The Science of Nature. 103(15).

Auer, S.K. and Martin, T.E. 2012. Climate change has indirect effects on resource use and overlap among coexisting bird species with negative consequences for their reproductive success. Global Change Biology. 19(2): 411-419.

Barrett, K., Nibbelink, N.P., Maerz, J.C. 2014. Identifying Priority Species and Conservation Opportunities Under Future Climate Scenarios: Amphibians in a Biodiversity Hotspot. Journal of Fish and Wildlife Management. 5(2): 282-297.

Brodie, J., Post, E., Watson, F., Berger, J. 2012. Climate change intensification of herbivore impacts on tree recruitment. Proc. R. Soc. B. 279: 1366-1370.

Carroll, C. 2007. Interacting Effects of Climate Change, Landscape Conversion, and Harvest on Carnivore Populations at the Range Margin: Marten and Lynx in the Northern Appalachians. Conservation Biology. 21(4): 1092-1104.

Christenson, L.M., Mitchell, M.J., Groffman, P.M., Lovett, G.M. 2014. Cascading Effects of Climate Change on Forest Ecosystems: Biogeochemical Links Between Trees and Moose in the Northeast USA. Ecosystems. 17: 442-457.

Corn, P.S. 2005. Climate change and amphibians. Animal Biodiversity and Conservation. 28.1:59-67.

Creutzburg, M.K., Henderson, E.B., Conklin, D.R. 2015. Climate change and land management impact rangeland condition and sage-grouse habitat in southeastern Oregon. AIMS Environmental Science. 2(2): 203-236.

Dawe, K.L., Bayne, E.M., Boutin, S. 2014. Influence of climate and human land use on the distribution of white-tailed deer (Odocoileus virginianus) in the western boreal forest. Can. J. Zool. 92: 353-363.

Dou, H., Jiang, G., Stott, P., Piao, R. 2013. Climate change impacts population dynamics and distribution shift of moose (Alces alces) in Heilongjiang Province of China. Ecol. Res. 28: 625-632.

Ellwood, E. R., A. Gallinat, R. B. Primack, and T. L. Lloyd-Evans. 2015. Autumn migration of North American landbirds. Pp. 193–205 in E. M. Wood and J. L. Kellermann ( editors), Phenological synchrony and bird migration: changing climate and seasonal resources in North America. Studies in Avian Biology (no. 47), CRC Press, Boca Raton, FL.

Groffman, P. M., P. Kareiva, S. Carter, N. B. Grimm, J. Lawler, M. Mack, V. Matzek, and H. Tallis. 2014. Ch. 8: Ecosystems, Biodiversity, and Ecosystem Services. Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G. W. Yohe, Eds., U.S.  Global Change Research Program. DOI:10.7930/J0TD9V7H.

Hoving, C.L., Lee, Y.M., Badra, P.J., Klatt, B.J. 2013. Changing Climate, Changing Wildlife: A Vulnerability Assessment of 400 Species of Greatest Conservation Need and Game Species in Michigan. Michigan Department of Natural Resources, Wildlife Division Report No. 3564.

Hoving, C.L. and Notaro, M. 2015. Ice, Snow, and Swamp: Managing Deer in Michigan’s Changing Climate. Michigan Journal of Sustainability. Volume 3, Spring: pp 101-110.

Koen, E.L., Bowman, J., Murray, D.L., Wilson, P.J. 2014. Climate change reduces genetic diversity of Canada lynx at the trailing range edge. Ecography. 37: 754-762.

Koen, E.L., Bowman, J., Wilson, P.J. 2015. Isolation of peripheral populations of Canada lynx (Lynx canadensis). Canadian Journal of Zoology. 93(7): 521-530.

Kozma, R., Melsted, P., Magnusson, K.P., Hoglund, J. 2016. Looking into the past – the reaction of three grouse species to climate change over the last million years using whole genome sequences. Molecular Ecology. 25(2): 570-580.

Li, Y., Cohen, J.M., Rohr, J.R. 2013. Review and synthesis of the effects of climate change on amphibians. Integrative Zoology. 8: 145-161.

Licht, D.S., Moen, R.A., Brown, D.P., Romanski, M.C., Gitzen, R.A. 2015. The Canada Lynx (Lynx canadensis) of Isle Royale: Over-harvest, Climate Change, and the Extirpation of an Island Population. The Canadian Field-Naturalist. 129: 139-151.

Loyola, R.D., Lemes, P., Brum, F.T., Provete, D.B., Duarte, L.D.S. 2014. Clade-specific consequences of climate change to amphibians in Atlantic Forest protected areas. Ecography. 37: 65-72.

Lučan, R.K., Weiser, M., Hanák, V. 2013. Contrasting effects of climate change on the timing of reproduction and reproductive success of a temperate insectivorous bat. Journal of Zoology. 290(2): 151-159.

Lusk, J.J., Guthery, F.S., DeMaso, S.J. 2001. Northern bobwhite (Colinus virginianus) abundance in relation to yearly weather and long-term climate patterns. Ecological Modelling. 146(1-3): 3-15.

Melin, M., Matala, J., Mehtatalo, L., Tiilikainen, R., Tikkanen, O., Maltamo, M., Pusenius, J., Packalen, P. Moose (Alces alces) reacts to high summer temperatures by utilizing thermal shelters in boreal forests – an analysis based on airborne laser scanning of the canopy structure at moose locations. Global Change Biology 20: 1115-1125.

Miller-Rushing, A.J., Lloyd-Evans, T.L., Primack, R.B., Satzinger, P. 2008. Bird migration times, climate change, and changing population sizes. Global Change Biology. 14: 1959-1972.

Monteith, K.L., Klaver, R.W., Herset, K.R., Holland, A.A., Thomas, T.P., Kauffman, M.J. 2015. Effects of climate and plant phenology on recruitment of moose at the southern extent of their range. Oecologia. 178: 1137-1148.

Murray, D.L., Steury, T.D., Roth, J.D. 2008. Assessment of Canada Lynx Research and Conservation Needs in the Southern Range: Another Kick at the Cat. The Journal of Wildlife Management. 72(7): 1463-1472.

National Wildlife Federation. 2013a. Nowhere to Run: Big Game Wildlife in a Warming World. Accessed online: http://www.nwf.org/~/media/PDFs/Global-Warming/Reports/NowheretoRun-BigGameWildlife-LowResFinal_110613.ashx

National Wildlife Federation. 2013b. Shifting Skies: Migratory Birds in a Warming World. Accessed online: https://www.nwf.org/pdf/Reports/NWF_Migratory_Birds_Report_web_Final.pdf

Niedzielski, B. and Bowman, J. 2015. Survival and cause-specific mortality of the female eastern wild turkey at its northern range edge. Wildlife Research. 41(7): 545-551.

Pease, A. and Paukert, C. n.d. Potential effects of climate change on smallmouth bass growth in streams of the central U.S. Accessed online: http://fishhabclimate.org/sites/default/files/documents/SMB%20growth%20fact%20sheet.pdf

Post, E. and Stenseth, N.C. 1998. Large-scale climatic fluctuation and population dynamics of moose and white-tailed deer. Journal of Animal Ecology. 67: 537-543.

Razgour, O., Juste, J., Ibanez, C., Kiefer, A., Rebelo, H., Puechmaille, S.J., Arlettaz, R., Burke, T., Dawson, D.A., Beaumont, M., Jones, G. 2013. The shaping of genetic variation in edge-of-range populations under past and future climate change. Ecology Letters. 16(10): 1258-1266.

Rodenhouse, N.L., Matthews, S.N., McFarland, K.P., Lambert, J.D., Iverson, L.R., Prasad, A., Sillett, T.S., Holmes, R.T. 2008. Potential effects of climate change on birds of the Northeast. Mitig. Adapt. Strat. Glob. Change. 13: 517-540.

Sherwin, H.A., Montgomery, W.I., Lundy, M.G. 2012. Review: The impact and implications of climate change for bats. Mammal Review. 43(3): 18pp.

Siegel, R.B., Pyle, P., Thorne, J.H., Holguin, A.J., Howell, C.A., Stock, S., Tingley, M.W. 2014. Vulnerability of birds to climate change in California’s Sierra Nevada. Avian Conservation & Ecology. 9(1), No. 7.

Street, G.M., Rodgers, A.R., Fryxell, J.M. 2015. Mid-day temperature variation influences seasonal habitat selection by moose. The Journal of Wildlife Management. 79(3): 505-512.

Tape, K.D., Christie, K., Carroll, G., O’Donnell, J.A. 2015. Novel wildlife in the Arctic: the influence of changing riparian ecosystems and shrub habitat expansion on snowshoe hares. Global Change Biology. 22(1): 12pp.

Tuberville, T.D., Andrews, K.M., Sperry, J.H., Grosse, A.M. 2015. Use of the NatureServe Climate Change Vulnerability Index as an Assessment Tool for Reptiles and Amphibians: Lessons Learned. Environmental Management. 56(4): 822-834.

Van Hemert, C., Pearce, J.M., Handel, C.M. 2014. Wildlife health in a rapidly changing North: focus on avian disease. Frontiers in Ecology and the Environment. 12(10): 548-556.

Williford, D., Deyoung, R.W., Honeycutt, R.L., Brennan, L.A., Hernandez, F. 2016. Phylogeography of the bobwhite (Colinus) quails. Wildlife Monographs. 193(1):1-49.

Wright, A.N., Schwartz, M.W., Hijmans, R.J., Shaffer, H.B. 2015. Advances in climate models from CMIP3 to CMIP5 do not change predictions of future habitat suitability for California reptiles and amphibians. Climatic Change. DOI 10.1007/s10584-015-1552-6

Wu, J. 2016. Detection and attribution of the effects of climate change on bat distributions over the last 50 years. Climatic Change. 134(4): 681-696.

Yan, C., Stenseth, N.C., Krebs, C.J., Zhang, Z. 2013. Linking climate change to population cycles of hares and lynx. Global Change Biology. 19: 3263-3271.

Zimova, M., Mills, L.S., Nowak, J.J. 2016. High fitness costs of climate change-induced camouflage mismatch. Ecology Letters. 19(3): 299-307.

Climate Change & Wildlife Impacts: Part 1

(click here to download a pdf of this full article or a one-page synopsis)

By Jennifer Hushaw

Climate change may soon outmatch traditional human influence as the biggest driver of change in biological diversity (i.e. biodiversity) over the coming century (Bellard et al. 2012; Jones et al. 2016). We will see dynamic changes as some species expand their ranges to take advantage of new suitable habitat, others shift into new regions and form novel species associations, and many others alter their physiology, behavior, or preferred range in an attempt to adapt to the changing conditions. Given that forests are home to 80% of the world’s terrestrial biodiversity (WWF 2015), the conservation and management of forestland has been, and will continue to be, a key part of efforts to maintain habitat for these species as they readjust. In this way, forest managers can help guard against the potential for biodiversity loss by enhancing forest health and ecosystem function through management.

This bulletin is the first in a two-part piece—it outlines the observed and expected climate change impacts for wildlife globally, as well as the forest management approaches that dovetail best with supporting at-risk species. Part two will delve more specifically into the anticipated climate impacts and wildlife management considerations for a number of key species in North America.

Climate Change & Wildlife Impacts

Climate change will impact wildlife directly through changes in temperature and water availability, and indirectly through effects on food sources, associated species, and habitat conditions. Some organisms will certainly benefit from the coming changes, while others may decline or even go extinct—depending (in large part) on the unique responses of individual species and populations (Staudinger et al. 2012). We will examine some specific examples in Part 2 of this bulletin, but the major ways climate change will affect wildlife include:

Transforming habitat

Changes in temperature, precipitation, and underlying vegetation will transform the habitat for many species. Extreme events may also induce shifts of entire ecosystems. Organisms with specific habitat requirements will not adapt as easily, while generalists will fare better.

Shifts in timing/seasonal changes

Changes in seasonality (e.g. shorter winters, earlier springs) may cause important species relationships to be out of sync, such as pollinators and their plants, predator-prey relationships, host-parasite relationships, etc. These changes can also affect the availability of food sources for migrating species and the optimal timing of reproduction for certain organisms.

Range shifts/migration

More mobile species will ‘follow’ their optimal climate conditions into new regions. As species ranges shift over time, we will see natural communities, species associations, and interactions that are entirely novel.

Spreading pests and disease

Climate-induced species shifts are expected to increase the frequency of new host-parasite associations and emerging infectious diseases, as new species come in contact with each other (Hoberg & Brooks 2015)—with implications for the health of human and wildlife populations. Warmer temperatures may also increase pathogens within intermediate hosts and vectors, or increase survival of animals that harbor disease (USGS 2012).

What makes wildlife species resilient to climate change?

There are particular characteristics that make species and populations more or less at risk from climate-related disturbance. The least at risk will have “tolerance to broad range of factors, such as temperature, water availability and fire,” a “high degree of phenotypic plasticity,” a “high degree of genetic variability,” “short generation times (rapid life cycles) and short time to sexual maturity,” high fertility, “‘generalist’ requirements for food, nesting sites, etc.,” “good dispersal ability,” and “broad geographic ranges.” In contrast, the most at risk species will have nearly opposite characteristics in each of these areas, e.g. poor dispersal and low genetic variability (Staudinger et al. 2012).


As the climate changes, many species will find that their current habitat is outside their climate niche—the full range of temperature and precipitation conditions in which they normally occur—and in order to adapt they must change where, when, or how they operate.

Where – Species can respond spatially by shifting their range and following their optimal climate conditions.

When – Species can respond temporally by changing their phenology, e.g. shifting the timing of key life cycle events.

How – Species can respond physiologically or behaviorally by developing tolerance to warmer/drier conditions or changing their diet, activity, or energy budget.

(Bellard et al. 2012)

In the short-term, these changes can happen through phenotypic plasticity, while in the long-term they will happen through evolution, but the rate of climate change may still be faster than the pace at which many species can effectively adapt.

Observed Changes

Changes in the phenology, range boundaries, and abundances of wildlife species have been documented across the globe. Over the past decade, synthesis studies have pulled this literature together to see whether current climate change has left a discernable fingerprint on the Earth’s biodiversity. The challenge for biologists is separating (relatively) small, systematic trends that might be caused by climate from short-term local changes that might be caused by land-use or natural species shifts (Parmesan & Yohe 2003). Taken together, the evidence suggests that climate change impacts are already being felt. In fact, the IPCC concluded (with high confidence) that: “Many terrestrial, freshwater, and marine species have shifted their geographic ranges, seasonal activities, migration patterns, abundances, and species interactions in response to ongoing climate change.” (IPCC 2014)

Observed changes and conclusions from these meta-analyses include:

  • Earlier spring events (bud burst, flowering, breaking hibernation, migrating, breeding)—documented on all but one continent and in all major oceans.
  • Changes in phenology that put an increasing number of predator-prey and insect-plant systems out-of-sync (with mostly negative consequences).
  • Documented examples on all continents (and in most of the major oceans) of warm-adapted communities expanding and individual species shifting their ranges poleward.
  • Range-restricted species (i.e. polar and mountaintop organisms) experience the biggest range contractions, with evidence of some actual extinctions. Tropical coral reefs and amphibians are the most negatively impacted.
  • These observed changes have been linked to climate change through long-term correlations between climate and biological variation, experiments in the field and laboratory, and basic physiological research.

(Parmesan 2006)

More recent work supports these results and suggests that species are migrating even faster than previously thought. In their meta-analysis, Chen et al. (2011) found that species moved away from the equator at a median rate of 16.9 km per decade and upslope at a median rate of 11.0m per decade. Overall, they found a significant shift toward higher latitudes and elevations (for 3/4 of species) and the shifts were largest where climate has warmed the most. Nevertheless, about one quarter of species actually shifted in the opposite direction, highlighting the diversity of species response and the fact that there are sometimes other competing drivers at work.

Model Projections  

The most recent report from the IPCC examined all the scientific evidence regarding impacts on the world’s biodiversity and concluded (with high confidence) that:

”A large fraction of both terrestrial and freshwater species faces increased extinction risk under projected climate change during and beyond the 21st century, especially as climate change interacts with other stressors, such as habitat modification, over-exploitation, pollution, and invasive species.”

They also noted that this risk will increase with the magnitude and rate of climate change (IPCC 2014).

There is limited evidence of extinctions caused by warming so far, but we know that slower, natural climate changes in the Earth’s past led to major ecosystem shifts and species extinctions, so there is reason to believe we will see similar (or even more severe) impacts under the rapid warming we’re experiencing now (IPCC 2014). As such, there has been a lot of research aimed at projecting species loss under climate change. Researchers use a wide variety of modeling techniques—from as simple as calculating a species’ current climate niche and seeing where it will be in the future, to capturing ecological processes or incorporating detailed physiological data. Each approach has its strengths and weaknesses, but most indicate “alarming consequences for biodiversity” (Bellard et al. 2012).

Importantly, we expect significant time-lags in species response (e.g. decades to centuries for vegetation), which can accumulate in ecosystems because of the way species interact with each other. This means that it is easy to underestimate the amount of biodiversity change at any given time and suggests that we should watch for non-linear changes in these ecological systems (Essl et al. 2015).

Forest Management Considerations  

Managing Wildlife Under Climate Change

It is now widely acknowledged that climate change should be an explicit consideration when setting conservation and wildlife management priorities because it will be such a major driver of change in the coming century. However, most of the approaches currently used to incorporate climate change into spatial conservation prioritizations are focused on the continuous and direct impacts of climate change, without accounting for either the discrete (e.g. extreme events) or indirect impacts (Jones et al. 2016)—a critical area for improvement.

More generally, there are a number of management strategies that can help promote the resilience of wildlife populations in a changing climate, which include:

  • Conserve a diversity of landscapes, in terms of topography and soils2
  • Protect/represent refugial habitats1,2
  • Prioritize ‘future habitat’1
  • Increase or enhance regional connectivity1,2
  • Increase heterogeneity1
  • Sustain ecosystem process and function2
  • Increase amount and connectivity of wildlands3
  • Aim for representation, resiliency, and redundancy—networks of intact habitat that represent full range of species and ecosystems in a given landscape3
  • Increase management for species in areas where they are expected to advance, e.g. northern range limits3
  • Reduce other, non-climatic stressors4
  • Establish habitat buffer zones and wildlife corridors4
  • Consider translocation of species to new areas and replanting disturbed areas with less climate-sensitive species4
  • Expand monitoring to consider longer-term changes4

(1Jones et al. 2016; 2Groves et al. 2012; 3USFS 2013; 4Glick et al. 2009)

Managing for Carbon vs. Wildlife

Forests are increasingly recognized as a critical component of climate change mitigation efforts because of their ability to sequester carbon, as evidenced by the inclusion of forests in the recent Paris Climate Accord, but there can sometimes be a tension between managing for carbon benefits and managing for biodiversity/wildlife.

For example, researchers examined the land-use implications of the emissions trajectories used by the IPCC, to see how our climate mitigation efforts might affect global biodiversity ‘hot spots’ and they found that these efforts were generally well-aligned with biodiversity protection because they reduced loss of vegetation cover. However, the most ambitious target (RCP 2.6) actually led to a loss of natural cover because it involves widespread conversion to bioenergy crops, in order to achieve net negative emissions—showing that climate and wildlife goals are not necessarily linked (Jantz et al. 2015).

Another recent analysis in Sweden (Felton et al. 2016) examined the tradeoffs between forest management strategies for climate change adaptation and mitigation and biodiversity goals for tree species composition, forest structure, and spatial/temporal forest patterns. They found that some strategies were definite win-wins, but there were also some notable conflicts, summarized below:

Felton et al 2016 Table

While the relative tradeoffs may differ slightly from region-to-region, this same framework can be used anywhere to assess the relative benefits of these strategies when there is a simultaneous goal of enhancing wildlife habitat. A useful approach is to focus on the win-wins and prioritize climate-focused management actions that are most consistent with biodiversity goals.


~            ~             ~             ~             ~


Bellard, C., Bertelsmeier, C., Leadley, P., Thuiller, W., Courchamp, F. 2012. Impacts of climate change on the future of biodiversity. Ecology Letters. 15: 365-377.

Chen, I-C., Hill, J.K., Ohlemüller, R., Roy, D.B., Thomas, C.D. 2011. Rapid Range Shifts of Species Associated with High Levels of Climate Warming. Science. 333:1024-1026.

Essl, F., Dullinger, S., Rabitsch, W., Hulme, P.E., Pyšek, P., Wilson, J.R.U., Richardson, D.M. 2015. Historical legacies accumulate to shape future biodiversity in an era of rapid global change. Diversity and Distributions. 1-14.

Felton, A., Gustafsson, L., Roberge, J.-M., Ranius, T., Hjälten, J., Rudolphi, J., Lindbladh, M., Weslien, J., Rist, L., Brunet, J., Felton, A.M. 2016. How climate change adaptation and mitigation strategies can threaten or enhance the biodiversity of production forests: Insights from Sweden. Biological Conservation. 194: 11-20.

Glick, P., Staudt, A., Stein, B. 2009. A New Era for Conservation: Review of Climate Change Adaptation Literature. National Wildlife Federation.

Groves, C.R., Game, E.T., Anderson, M.G., Cross, M., Enquist, C., Ferdaña, Z., Girvetz, E., Gondor, A., Hall,

K.R., Higgins, J., Marshall, R., Popper, K., Schill, S., Shafer, S.L. 2012. Incorporating climate change into systematic conservation planning. Biodivers. Conserv. 21: 1651-1671.

Hoberg, E.P. and Brooks, D.R. 2015. Evolution in action: climate change, biodiversity dynamics and emerging infectious disease. Philosophical Transactions B. 370: 20130553.

IPCC, 2014: Summary for policymakers. In: Climate Change 2014: Impacts, Adaptation, and Vulnerability. Part A: Global and Sectoral Aspects. Contribution of Working Group II to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Field, C.B., V.R. Barros, D.J. Dokken, K.J. Mach, M.D. Mastrandrea, T.E. Bilir, M. Chatterjee, K.L. Ebi, Y.O. Estrada, R.C. Genova, B. Girma, E.S. Kissel, A.N. Levy, S. MacCracken, P.R. Mastrandrea, and L.L.White (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, pp. 1-32

Jantz, S.M., Barker, B., Brooks, T.M., Chini, L.P., Huang, Q., Moore, R.M., Noel, J. Hurtt, G.C. 2015. Future habitat loss and extinctions driven by land-use change in biodiversity hotspots under four scenarios of climate-change mitigation. Conservation Biology. 29(4):1122-31.

Jones, K.R., Watson, J.E.M., Possingham, H.P., Klein, C.J. 2016. Incorporating climate change into spatial conservation prioritisation: A review. Biological Conservation. 194: 121-130.

Parmesan, C. 2006. Ecological and Evolutionary Responses to Recent Climate Change. The Annual Review of Ecology, Evolution, Systematics. 37:637-69.

Parmesan, C. and Yohe, G. 2003. A globally coherent fingerprint of climate change impacts across natural systems. Nature. 421:37-42.

Staudinger, M.D., Grimm, N.B., Staudt, A., Carter, S.L., Chapin III, F.S., Kareiva, P., Ruckelshaus, M., Stein, B.A. 2012. Impacts of Climate Change on Biodiversity, Ecosystems, and Ecosystem Services: Technical Input to the 2013 National Climate Assessment. Cooperative Report to the 2013 National Climate Assessment. 296 p. Available at: http://assessment.globalchange.gov

US Forest Service. 2013. Climate Change Adaptation and Mitigation Management Options: A Guide for Natural Resource Managers in Southern Forest Ecosystems. [Vose, J.M., Klepzig, K.D (eds.)]. CRC Press.

US Geological Survey. 2012. Climate Change and Wildlife Health: Direct and Indirect Effects. Fact Sheet 2010–3017, revised 2012.

World Wildlife Fund. 2015. “Forest Habitat: Overview.” Accessed January 15, 2015.  http://www.worldwildlife.org/habitats/forest-habitat.

Climate Change and Extreme Weather, Part 2: Forest Impacts

(click here to download a pdf of the full article or a one-page synopsis)

By Jennifer Hushaw

In Part I of this bulletin, we described why and how we expect to see an increase in the frequency and intensity of some extreme weather and climate events as the planet warms. We examined the observed and projected trends in extreme heat, heavy precipitation, drought, and flooding. These extremes are likely to have a more immediate and drastic impact on our forests than long-term change in average conditions because they can trigger disturbance events that affect the health and composition of natural communities.

Extremes Shape Plant Communities

Long-term, gradual changes in average conditions are important for driving vegetation change, as we have discussed, but research also suggests that extremes play an equal or greater role in shaping the distribution, survival, productivity, and diversity of plant communities (Reyer et al. 2012). For example, a 2012 study found that growth in European forests for the past 500 years (based on extensive tree-ring data) responded synchronously to extreme climatic events during that period (Babst et al. 2012). This linkage between forest growth and extremes is likely to become even more important going forward, as we experience the increase in extremes discussed in Part I.

On a smaller scale, individual plant processes are also affected differently by extremes than by changing average conditions. For example, an increase in average temperature can affect phenology by lengthening the growing season and causing earlier leaf unfolding, but a change in variability in the form of early and late frosts can increase the risk of (possibly lethal) frost damage. Likewise, plant water relations can be disproportionately affected by extremes—an increase in night-time warming and average temperature can cause a slight increase in stomatal conductance, whereas an extreme event like drought can actually lead to mortality via stomatal closure and carbon starvation or hydraulic failure (Reyer et al. 2012). In this way, extremes are likely to play an outsized role in inducing the vegetation shifts researchers have been predicting.

Impact of Extremes on Forests


Of all the climate and weather extremes discussed here, drought receives the overwhelming amount of concern, attention, and research focus. There have been many studies conducted in southern Europe and southwestern United States in particular—both regions where climate models consistently project an increase in the frequency and intensity of future drought. In Europe, for example, researchers have found evidence of a widespread increase in crown defoliation between 1987 and 2007 due to drought, with long-term chronic effects that were most pronounced on drier sites (Carnicer et al. 2011).

U.S. Drought Impacts

In the US, much of the research on drought-related mortality has taken place in the semi-arid forests of the southwest, which provide a useful natural experiment because they are “highly vulnerable to climate-warming-induced drought” (Kolb 2015). These forests have already experienced drought-induced mortality in the form of large-scale die-off of piñyon-juniper woodlands, with an estimated 2.5 million acres affected (Peterman et al. 2013). A number of studies in this region have attempted to identify moisture thresholds (in terms of precipitation-evapotranspiration index, precipitation, vapor pressure deficit, tree-ring-based index of forest drought stress, pre-dawn leaf water potential, and others) that successfully predict tree mortality due to drought (Huang et al. 2015; Clifford et al. 2013; Williams et al. 2012; McDowell et al. 2015). When these thresholds are applied to future climate projections, the results generally point to massive forest mortality later in the century, e.g. McDowell et al. (2015) averaged a number of different modelling approaches and found that 72% of the needleleaf evergreen tree forests in the southwest US will experience mortality by 2050, with nearly 100% forest mortality by 2100.

CA-drought_Asner-et-al-2015California has also been in the spotlight for drought impacts in recent years, including a new study that found 10.6 million hectares of forest experienced measurable loss in canopy water content during the recent drought, with 1 million of those hectares experiencing severe water losses of greater than 30% (Asner et al. 2015). The California drought is illustrative of the types of droughts (and related impacts) we are likely to see more of in the future, as recent research has shown that anthropogenic warming contributed to the severity of the current drought and is increasing the probability of these co-occurring warm-dry conditions (Diffenbaugh et al. 2015). The drought impacts in California are also a great example of the worrisome ‘layering of stressors’ that can occur under these conditions, i.e. drought stresses trees, making them more vulnerable to insect attack, which ultimately increases mortality and the fuel loads to support massive wildfires.

The Real Risk of Climate Change-Type Drought

Despite the obvious risk from hotter drought, there are some natural processes that help stabilize plant populations after these types of disturbance events, such as self-thinning that reduces competition from neighbors, competition release through better adult reproductive performance, or phenotypic variability that helps mitigate mortality. These promote resilience by helping to balance the mortality caused by the event with better survival or increased recruitment (Lloret et al. 2012). These kinds of processes can be harnessed for adaptation purposes or used to help identify forests that are inherently more resilient. Given that not every extreme event leads to a shift in vegetation and these counterbalancing processes are often at work, there is some reason to be optimistic.

However, a recent comprehensive review of the literature suggests that the global outlook is generally negative—Allen et al. (2015) examined all the evidence suggesting that forests are more vulnerable to drought, e.g. trees die faster under warmer drought conditions, evolution is too slow relative to projected change, models are over-optimistic because mortality processes are not sufficiently represented, as well as all the evidence that forests are less vulnerable, e.g. physiological acclimation and adaptation capacities are large, species diversity and microsite variation can buffer mortality, CO2 fertilization and water-use efficiency can compensate for drought and heat stress. When all the pertinent issues were examined, they concluded we are most likely underestimating global vulnerability to hotter drought. Their conclusion was based, in part, on the fact that a number of drivers that are known with high confidence all point toward greater vulnerability, in particular:

  • Droughts eventually occur everywhere.
  • Warming produces hotter droughts.
  • Atmospheric moisture demand increases nonlinearly with temperature during drought.
  • Mortality can occur faster in hotter drought, consistent with fundamental physiology.
  • Shorter droughts occur more frequently than longer droughts and can become lethal under warming, increasing the frequency of lethal drought nonlinearly.
  • Mortality happens rapidly relative to growth intervals needed for forest recovery.

As we have discussed previously, drought risk actually varies with location, site characteristics, and forest type—see our previous bulletin for more detail on evaluating drought risk.

Extreme Heat

In an earlier bulletin, we explored how extreme heat affects plants at the cellular, leaf, and whole plant level, showing that trees have a variety of physiological and morphological responses that help them cope with extreme heat stress. While many species can behave plastically or increase their heat-tolerance by acclimating to warmer temperatures, there are, of course, limits to how adaptable trees can be in the face of these extremes.

Drought-induced forest die-off receives more attention in the scientific literature, but it is recognized that the trend of increasing hot temperature extremes will also pose problems for forests worldwide. As stated by Teskey et al. (2014): “Mortality from drought is far more likely than mortality from heat stress, but the severity of drought stress, and the speed of its onset, is greatly increased under high temperatures.” This is primarily because of the effect of temperature on vapour pressure deficit (VPD)—a key variable in plant water stress. VPD is essentially a combination of temperature and relative humidity that represents the ‘drying power’ of the air (technically, it is the difference between the amount of moisture in the air and how much moisture the air can hold when it is saturated, or the vapour pressure in the air compared to the vapour pressure in the leaves). Generally, the higher the VPD the more water plants lose through transpiration. A number of studies have highlighted the critical role of VPD in determining the level of forest drought stress (Breshears et al. 2013; McDowell et al. 2015; Williams et al. 2012) and they suggest that rising VPD is “potentially the largest threat to survival” (McDowell et al. 2015) because climate models consistently predict that VPD and temperature will increase and we have confidence in those projections.

Floods/Heavy Preciptiation

While excess water (due to flooding or water-logged soils) is on the other end of the spectrum from severe drought, it can have similar negative consequences, especially for species that are not well-adapted to those conditions. This includes (paradoxically) decreased water absorption, stomatal closure that reduces CO2 uptake and growth, and low oxygen conditions in the soil that inhibit root respiration (Reyer et al. 2013). This kind of forest stress is likely to increase in many places during the next century, as we experience large flood events, especially in the Northeast and Midwest regions highlighted in Part I of this bulletin, and more heavy precipitation. Although, in the U.S., the effects are likely to be greatest in those regions with the least flood tolerant species mix.

Note: We recommend referencing Russell et al. 2014 for maps of average flood tolerance and diversity of flood tolerance among tree species in the eastern U.S.

Extremes Can Have Big Implications for the Global Carbon Budget

Most coupled carbon-climate models (e.g. CMIP5 used in the most recent IPCC Assessment Report) show vegetation productivity and carbon sinks increasing in temperate and boreal regions. Although, new research is suggesting that extreme events and associated disturbances can offset or reverse that trend—“even a small shift in the frequency or severity of climate extremes could substantially reduce carbon sinks and may result in sizeable positive feedbacks to climate warming” (Reichstein et al. 2013).

Extremes can increase the risk of accelerated climate change if large-scale changes in terrestrial ecosystems, such as forest die-off or extensive wildfires, create feedbacks with the climate system.  For a sense of the scale, view this map from Reichstein et al. 2013, which shows areas where extreme events caused a large decrease in gross primary productivity between 1982 and 2011 (color indicates the cause: water scarcity = blue, extreme high temperatures = red, both = pink, neither = grey, and darker colors indicate greater losses).



Extremes are likely to have an outsized influence on vegetation communities and are likely to be the source of the most immediate climate change impacts in our forests. In particular, the risk of more impactful drought due to the combination of warmer temperatures and reduced precipitation (or changes in seasonality) will make certain regions, such as the southwest U.S., particularly vulnerable to large-scale forest die-off events. In other regions, extreme events may contribute to an increase in forest stress that can reduce productivity or increase vulnerability to other stressors, including insect outbreaks. Critically, the risk of these extreme heat and precipitation events will increase rapidly as average temperatures continue to rise.

~            ~             ~             ~             ~


Allen, C.D., Breshears, D.D., McDowell, N.G. 2015. On underestimation of global vulnerability to tree mortality and forest die-off from hotter drought in the Anthropocene. Ecosphere. 6 (8): 129. http://dx.doi.org/10.1890/ES15-00203.1

Asner, G.P, Brodrick, P.G., Anderson, C.B., Vaughn, N., Knapp, D.E., Martin, R.E. 2015. Progressive forest  canopy water loss during the 2012-2015 California drought. Proc. Natl. Acad. Sci. 113 (2): 7pp.

Babst, F., Carrer, M., Poulter, B., Urbinati, C., Neuwirth, B., Frank, D. 2012. 500 years of regional forest growth variability and links to climatic extreme events in Europe. Environ. Res. Lett. 7: 045705 (11pp).

Breshears, D.D., Adams, H.D., Eamus, D., McDowell, N.G., Law, D.J., Will, R.E., Williams, A.P., Zou, C.B. The critical amplifying role of increasing atmospheric moisture demand on tree mortality and associated regional die-off. Frontiers in Plant Science. 4 (266): 1-4.

Carnicer, J., Coll, M., Ninyerola, M., Pons, X., Sánchez, G., Peñuelas, J. 2011. Widespread crown condition decline, food web disruption, and amplified tree mortality with increased climate change-type drought. Proc. Natl. Acad. Sci. 108 (4): 1474-1478.

Clifford, M.J., Royer, P.D., Cobb, N.S., Breshears, D.D., Ford, P.L. 2013. Precipitation thresholds and drought-induced tree die-off: insights from patterns of Pinus edulis mortality along an environmental gradient. New Phytologist. 200: 413-421.

Diffenbaugh, N.S., Swain, D.L., Touma, D. 2015. Anthropogenic warming has increased drought risk in California. Proc. Natl. Acad. Sci. 112 (13): 3931-3936.

Huang, K., Yi, C., Wu, D., Zhou, T., Zhao, X., Blanford, W.J., Wie, S., Wu, H., Ling, D., Li, Z. 2015 Tipping point of a conifer forest ecosystem under severe drought. Environ. Res. Lett. 10 (2), Article ID: 024011.

Kolb, Thomas, E. 2015. A new drought tipping point for conifer mortality. Environ. Res. Lett. 10: 031002. DOI: 10.1088/1748-9326/10/3/031002

Lloret, F., Escudero, A., Iriondo, J.M., Martínez-Vilalta, J., Valladares, F. 2012. Extreme climatic events and vegetation: the role of stabilizing processes. Global Change Biology. 18: 797-805. DOI: 10.1111/j.1365-2486.2011.02624.x

McDowell, N.G., Williams, A.P., Xu, C., Pockman, W.T., Dickman, L.T., Sevanto, S., Pangle, R., Limousin, J., Plaut, J., Mackay, D.S., Ogee, J., Domec, J.C., Allen, C.D., Fisher, R.A., Jiang, X., Muss, J.D., Breshears, D.D., Rauscher, S.A., Koven, C. 2015. Multi-scale predictions of massive conifer mortality due to chronic temperature rise. Nature Climate Change. Advance Online Publication. DOI: 10.1038/NCLIMATE2873.

Peterman, W., Waring, R.H., Seager, T., Pollock, W.L. 2013. Soil properties affect pinyon pine – juniper response to drought. Ecohydrol. 6: 455-463.

Reichstein, M., Bahn, M., Ciais, P., Frank, D., Mahecha, M.D., Seneviratne, S.I., Zscheischler, J., Beer, C., Buchmann, N., Frank, D.C., Papale, D., Rammig, A., Smith, P., Thonicke, K., van der Velde, M., Vicca, S., Walz, A. Wattenbach, M. 2013. Climate extremes and the carbon cycle. Nature. 500: 287-295. DOI: 10.1038/nature12350.

Reyer, C.P.O., Leuzinger, S., Rammig, A., Wolf, A., Bartholomeus, R.P., Bonfante, A., de Lorenzi, F., Dury, M., Gloning, P., Aboujaoudé, R., Klein, T., Kuster, T.M., Martins, M., Niedrist, G., Riccardi, M., Wohlfahrt, G., de Angelis, P., de Dato, G., François, L., Menzel, A., Pereira, M. 2013. A plant’s perspective of extremes: terrestrial plant responses to changing climatic variability. Global Change Biology. 19: 75-89. DOI: 10.1111/gcb.12023

Russell, M.B., Woodall, C.W., D’Amato, A.W., Domke, G.M., Saatchi, S.S. 2014. Beyond mean functional traits: Influence of functional trait profiles on forest structure, prodiction, and mortality across the eastern US. Forest Ecology and Management. 328: 1-9.

Teskey, R., Wertin, T., Bauweraerts, I., Ameye, M., McGuire, M.A., Steppe, K. 2014. Responses of tree species to heat waves and extreme heat events. Plant, Cell and Environment. DOI: 10.1111/pce/12417.

Williams, A.P., Allen, C.D., Macalady, A.K., Griffin, D., Woodhouse, C.A., Meko, D.M., Swetnam, T.W., Rauscher, S.A., Seager, R., Grissino-Mayer, H.D., Dean, J.S., Cook, E.R., Gangodagamage, C., Cai, M., McDowell, N.G. 2013. Temperature as a potent driver of regional forest drought stress and tree mortality. Nature Climate Change. 3: 292-297.