Peer Review Draft 10/19/16 “THIS INFORMATION IS DISTRIBUTED SOLELY FOR THE PURPOSE OF PRE-DISSEMINATION PEER REVIEW UNDER APPLICABLE INFORMATION QUALITY GUIDELINES. IT HAS NOT BEEN FORMALLY DISSEMINATED BY [THE AGENCY]. IT DOES NOT REPRESENT AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY AGENCY DETERMINATION OR POLICY.” 1 Chapter 2: Climate, Disturbance, and Vulnerability to 2 Vegetation Change in the Northwest Forest Plan Area 3 4 Matthew J. Reilly1, Thomas A. Spies2, Jeremy Littell3, Ramona Butz4, and John Kim5 5 6 7 Introduction 8 Climate change is expected to alter the structure and function of forested ecosystems in the 9 United States (Vose et al. 2012). Increases in atmospheric concentrations of CO2 and 10 corresponding increases in temperature and fire activity over the next century are expected to 11 have profound effects on biodiversity and the delivery of ecosystem services within the 12 Northwest Forest Plan (NWFP) area. The effects of climate change on ecological processes may 13 occur through a variety of mechanisms at a range of spatial scales and levels of biological 14 organization from the physiological responses of individuals to the composition and structure of 15 stands and landscapes (Peterson et al. 2014). The ecological interactions and diversity of 16 biophysical settings in the region are complex. Understanding and incorporating how climate 17 change projections and potential effects vary within the region (e.g., Deser et al. 2012) will be 18 essential in mitigating effects and developing strategies for adaptation and mitigation. 19 20 21 22 23 24 1 Matthew Reilly is a Postdoctoral Scholar, Oregon State University, College of Forestry, Corvallis, 25 Oregon; 2 Thomas Spies is a is a Senior Scientist, United States Forest Service, Pacific Northwest Research 26 Station, Corvallis, Oregon; 3 Jeremy Littell is a Research Scientist, U.S. Geological Survey, Alaska Climate Science 27 Center, Anchorage, Alaska; 4 Ramona Butz is an Ecologist, U.S. Forest Service, Region 5, Eureka, California; 5 John 28 Kim is a Biological Scientist, U.S. Forest Service, Pacific Northwest Research Station, Corvallis, Oregon; 1 Peer Review Draft 10/19/16 “THIS INFORMATION IS DISTRIBUTED SOLELY FOR THE PURPOSE OF PRE-DISSEMINATION PEER REVIEW UNDER APPLICABLE INFORMATION QUALITY GUIDELINES. IT HAS NOT BEEN FORMALLY DISSEMINATED BY [THE AGENCY]. IT DOES NOT REPRESENT AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY AGENCY DETERMINATION OR POLICY.” 1 Background and Setting 2 The Northwest Forest Plan area covers approximately 24.4 million acres and includes several 3 physiographic provinces (fig. 1) that encompass a broad range of environmental and climatic 4 gradients (fig. 2). Temperature is cooler and wetter towards the north in the coastal and inland 5 mountains, but transitions to a more Mediterranean climate with warmer, drier summers and 6 greater inter-annual variability to the south (fig. 3). Most precipitation in the region falls during 7 the winter months, often as snow at higher elevations. The Olympic Peninsula, Western 8 Lowlands, and Coast Range are located in the western portion of the region. These receive the 9 greatest annual precipitation and often experience a summer fog layer that can partially moderate 10 summer moisture stress. The crest of the Cascade Mountain Range extends from northern 11 Washington to northern California, bisecting much of the region and creating a steep gradient in 12 precipitation. The wetter Western Cascades encompass a wide range of elevations and 13 temperature and precipitation which generally decrease toward the south. The Eastern Cascades 14 extend in a narrow band from Washington to California and are generally much drier than the 15 Western Cascades and most of the NWFP area. The Klamath Mountains, in southwestern 16 Oregon and Northwest California, comprise the most climatically and geologically diverse 17 province in the area, with a strong west-to-east gradient in precipitation and summer moisture 18 stress. The Willamette Valley makes up a smaller portion of the NWFP area and is 19 predominantly non-forested. 20 2 Peer Review Draft 10/19/16 “THIS INFORMATION IS DISTRIBUTED SOLELY FOR THE PURPOSE OF PRE-DISSEMINATION PEER REVIEW UNDER APPLICABLE INFORMATION QUALITY GUIDELINES. IT HAS NOT BEEN FORMALLY DISSEMINATED BY [THE AGENCY]. IT DOES NOT REPRESENT AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY AGENCY DETERMINATION OR POLICY.” 1 2 Figure 1—Geographic distribution of potential vegetation zones (Simpson 2013) and ecoregions 3 in the Northwest Forest Plan area. Map credit: Ray Davis. 4 3 Peer Review Draft 10/19/16 “THIS INFORMATION IS DISTRIBUTED SOLELY FOR THE PURPOSE OF PRE-DISSEMINATION PEER REVIEW UNDER APPLICABLE INFORMATION QUALITY GUIDELINES. IT HAS NOT BEEN FORMALLY DISSEMINATED BY [THE AGENCY]. IT DOES NOT REPRESENT AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY AGENCY DETERMINATION OR POLICY.” 1 The broad range of environmental and climatic gradients is reflected in the distribution of 2 several potential vegetation zones across the region (figs. 2 and 3) (Simpson 2013, available 3 from www.ecoshare.info/category/gis-data-vegzones). Vegetation zones have a unique species 4 pool with similar but internally variable biophysical conditions and historical disturbance 5 regimes that vary geographically (Winthers et al. 2005). Potential vegetation zones represent 6 climax vegetation types that would eventually develop in the absence of disturbance, therefore 7 existing or current vegetation varies often within zones depending on seral stage and time since 8 disturbance. For example, the most abundant vegetation zone in the NWFP area, western 9 hemlock (Tsuga occidentalis), is currently dominated primarily by Douglas-fir (Psuedostuga 10 menziesii). Vegetation zones provide an ecological framework for discussing climate and 11 vegetation change across broad geographic extents. They have common pathways of structural 12 development that differ in complexity and reflect regional gradients in productivity as well as 13 historical and contemporary disturbance regimes (Reilly and Spies 2015). 14 Major vegetation zones (fig. 4) generally correspond to those presented by Franklin and 15 Dyrness (1973) and were initially broken into moist and dry forests in the NWFP. This 16 characterization is overly simplistic as annual precipitation in any given zone varies 17 geographically. Moist vegetation zones make up approximately 60 percent of the region, and are 18 primarily located in the coastal areas and west of the Cascade Crest. These include Sitka spruce 19 (Picea sitchensis) and redwood (Sequoia sempervirens), tanoak (Lithocarpus densiflorus), 20 western hemlock, Pacific silver fir (Abies amabilis), and mountain hemlock (Tsuga 21 mertensiana). Dry forest vegetation zones are located east of the Cascade Crest and also 22 comprise a large portion of inland areas in southwestern Oregon and northwestern California. 23 They include western juniper (Juniperus occidentalis), ponderosa pine (Pinus ponderosa), 24 Douglas-fir, grand fir (Abies grandis) and white fir (Abies concolor), and subalpine forests 25 dominated by subalpine fir (Abies lasiocarpa), Engelmann spruce (Picea engelmanii), and 26 whitebark pine (Pinus albicaulis). More information on geographic variability and current 27 vegetation in Oregon and Washington is available at: www.ecoshare.info/publications. Appendix 28 1 provides crosswalk between the Simpson vegetation zones (2013) and existing vegetation in 29 northern California based on Regional Dominance 1 in the Region 5 CALVEG 30 database: http://www.fs.usda.gov/detail/r5/landmanagement/resourcemanagement/?cid=stelprdb 31 5347192. 4 Peer Review Draft 10/19/16 “THIS INFORMATION IS DISTRIBUTED SOLELY FOR THE PURPOSE OF PRE-DISSEMINATION PEER REVIEW UNDER APPLICABLE INFORMATION QUALITY GUIDELINES. IT HAS NOT BEEN FORMALLY DISSEMINATED BY [THE AGENCY]. IT DOES NOT REPRESENT AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY AGENCY DETERMINATION OR POLICY.” 1 2 Figure 2—Maps of major environmental and climatic gradients across the Northwest Forest Plan 3 area including a) elevation, b) annual precipitation, and c) annual temperature. Temperature and 4 precipitation are derived from 800-meter monthly PRISM (Parameter-elevation Regressions on 5 Independent Slopes Model) grids averaged over 30 years (1971-2000) and were obtained from 6 the Landscape Ecology, Modeling, Mapping and Analysis group at Oregon State University. 5 Peer Review Draft 10/19/16 “THIS INFORMATION IS DISTRIBUTED SOLELY FOR THE PURPOSE OF PRE-DISSEMINATION PEER REVIEW UNDER APPLICABLE INFORMATION QUALITY GUIDELINES. IT HAS NOT BEEN FORMALLY DISSEMINATED BY [THE AGENCY]. IT DOES NOT REPRESENT AND SHOULD NOT BE CONSTRUED TO REPRESENT ANY AGENCY DETERMINATION OR POLICY.” 1 2 Figure 3—Maps of gradients in summer climate across the Northwest Forest Plan area including 3 a) summer temperature, b) summer precipitation, c) summer moisture stress, and d) summer fog. 4 Temperature and precipitation are derived from 800-meter monthly PRISM (Parameter-elevation 5 Regressions on Independent Slopes Model) grids averaged over 30 years (1971-2000) and were 6 obtained from the Landscape Ecology, Modeling, Mapping and Analysis group at Oregon State 7 University. Summer moisture stress was calculated by dividing summer temperature by summer 8 precipitation. Summer fog is proxy based on the optimal path length from coastline and is 9 modified by terrain blockage (Daly et al. 2008). 10 11 12 13 14 15 16 6 Peer Review Draft 10/19/16