Climate Change Vulnerability and Adaptation

Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region Robert E. Keane, Mary Frances Mahalovich, Barry L. Bollenbacher, Mary E. Manning, Rachel A. Loehman, Terrie B. Jain, Lisa M. Holsinger, Andrew J. Larson, and Meredith M. Webster Introduction simply shift to other areas of the landscape or become rare. Juxtaposed with climate change concerns are the consequences of other land management policies and past The projected rapid changes in climate will affect the activities, such as fire exclusion, fuels treatments, and graz- unique vegetation assemblages of the Northern Rockies ing. A thorough assessment of the responses of vegetation region in myriad ways, both directly through shifts in veg- to projected climate change is needed, along with an evalua- etation growth, mortality, and regeneration, and indirectly tion of the vulnerability of important species, communities, through changes in disturbance regimes and interactions and vegetation-related resources that may be influenced by with changes in other ecosystem processes, such as hydrol- the effects, both direct and indirect, of climate change. This ogy, snow dynamics, and exotic invasions (Bonan 2008; assessment must also account for past management actions Hansen and Phillips 2015; Hansen et al. 2001; Notaro et and current vegetation conditions and their interactions with al. 2007). These impacts, taken collectively, could change future climates. the way vegetation is managed by public land agencies in This chapter addresses the potential impacts of climate this area. Some species may be in danger of rapid decreases change on forest vegetation in the Forest Service, U.S. in abundance, while others may undergo range expansion Department of Agriculture (USFS) Northern Region and (Landhäusser et al. 2010). New vegetation communities the Greater Yellowstone Area (GYA), hereafter called the may form, while historical vegetation complexes may Northern Rockies region (fig. 6.1). Then, based on the Figure 6.1—The Northern Rockies (NR) assessment area that includes the Northern Region of the U.S. Forest Service and the Greater Yellowstone Area (Yellowstone National Park and surrounding areas). Presented are existing vegetation types by the five geographic sub-areas used to stratify assessments in this report. This map was created from the LANDFIRE Existing Vegetation Type map by aggregating the National Vegetation Classification Standard vegetation types into a set of vegetation types that has some meaning across the NR at this coarse scale. This map is intended to convey current vegetation of the NR. 128 USDA Forest Service RMRS-GTR-374. 2018 Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region climate impacts assessment, we present an evaluation of the 30-year weather patterns of a region. Climate variability vulnerability of important tree species, vegetation types, is the variation in weather statistics over relatively broad and resources of concern to projected climate change ef- regions and long time periods. Climate variability can be fects. Last, we present various adaptation actions to address caused by underlying climatic processes, such as changes climate change vulnerabilities. in patterns of ocean temperatures. The El Niño-Southern This chapter has six major sections. In the introductory Oscillation (ENSO) and the Pacific Decadal Oscillation section, we define terminology used throughout the chapter (PDO), for example, are two sources of climate variability and provide background material on the details of the in western North America (Newman et al. 2003). ENSO assessment including the scales, geographic areas, and perti- oscillations occur over 2- to 7-year periods (Gershunov and nent information used to make our assessments. We discuss Barnett 1998), while PDO oscillations occur on a longer cy- how to evaluate uncertainty in climate change projections cle (20–50 years) (Heyerdahl et al. 2002). External forcings, and vegetation response. We also summarize the methods such as changes in solar radiation, large volcanic eruptions, used to make projections of vegetation response to changing and increasing concentrations of greenhouse gases in the at- climate. The second section contains important ecological mosphere, also influence climate variability. Climate change background information that was used to assess climate is a nonrandom change in climate that is measured over change impacts and projected climate change responses for several decades or longer. It is technically defined as a sta- 17 tree species, 5 forest vegetation types, and 3 resources of tistically significant variation in either the mean state of the concern. The third section presents information on the tree climate or in its variability, persisting for an extended period species, types, or resources of concern that are important (decades or longer). Like climate variability, climate change when evaluating climate change responses. In the fourth may be due to natural internal processes or to external forc- section, we rate the vulnerability of the species, vegetation ings. A climate scenario is a plausible and often simplified types, and resources of concern to climate change using representation of one possible future climate, based on a information from the third section. In the fifth section, we consistent set of known principles about the climate system discuss adaptation strategies and management actions that used as input to climate models. can be used to address likely impacts of climate change. The final section is a concluding discussion. Vegetation This chapter uses the best available information about Several general terms are used in vegetation ecology climate change effects on vegetation in the Northern to describe how ecosystems respond to climate change Rockies. We have integrated broad-scale modeling results (Intergovernmental Panel on Climate Change [IPCC] 2007). with a detailed synthesis of climate change literature for the Adaptive capacity is the ability of a plant, species, or system region. This chapter was written to aid land managers in ad- to adjust to climate change (including climate variability dressing climate change effects on forest vegetation in land and extremes) to moderate potential damages, to take ad- management planning and development of management vantage of opportunities, or to cope with the consequences. strategies. This chapter does not include the detail needed Exposure is the nature and degree to which a system is to address climate change effects at the project level, but it exposed to significant climate variations (Glick et al. 2010). does include valuable information and syntheses that can be Sensitivity is the degree to which a system is affected, either used in project planning and in addressing broad concerns at adversely or beneficially, by climate variability or change. large spatial scales. The effect may be direct, such as crop yield decreases in response to a higher temperature, or indirect, such as damage Terminology caused by an increase in the frequency of coastal flooding due to sea-level rise. Resilience is the degree to which eco- Climate systems can recover from one or more disturbances without Evaluations of climatic trends can be confusing, mostly a major shift in composition or function, whereas resistance because weather and climate vary at different spatial is the ability of an organism, population, community, or eco- and temporal scales. To reduce this confusion, it is often system to withstand perturbations without significant loss helpful to clearly define the terms and explain the scales of structure or function (i.e., remain unchanged) (Holling that distinguish weather, climate variability, and climate 1973; Seidl et al. 2016). From a management perspective, change. Weather is the hourly, daily, weekly, or monthly resistance includes (1) the degree to which communities are summaries in temperature, precipitation, wind, humidity, able to resist change, such as that from warming climates, and other atmospheric conditions observed at a given place and (2) the manipulation of the physical environment to or across a large region. Weather changes at relatively small counteract and resist physical and biological change (i.e., temporal scales (quickly) and it can change significantly cutting, burning, harvest treatments). Vulnerability is the as one moves north or south, east or west, or up and down degree to which a system is susceptible to, and unable to in elevation. Weather is difficult to predict more than a cope with, the adverse effects of climate change, including few days in advance. Climate is a statistical characteriza- associated climate variability and extremes. Vulnerability is tion of the weather, averaged over many years. The World a function of the character, magnitude, and rate of climate Meteorological Organization defines it as the average USDA Forest Service RMRS-GTR-374. 2018 129 Chapter 6: Effects of Climate Change on Forest Vegetation in the Northern Rockies Region change and variation to which a system is exposed, its sensi- 3. Achieve long-term ecological sustainability and tivity, and its adaptive capacity. provide a broad range of ecosystem services to Other terms describe how ecosystem processes that are society. affected by climate change will influence vegetation. In The USFS emphasizes ecosystem restoration across all general, stressors are any physical, chemical, or biologi- National Forest System lands with the goal of attaining

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