Climate change implications in the northern coastal temperate rainforest of North America

Climate change implications in the northern coastal temperate rainforest of North America Colin S. Shanley 0 1 2 3 4 5 6 7 8 9 10 Sanjay Pyare 0 1 2 3 4 5 6 7 8 9 10 Michael I. Goldstein 0 1 2 3 4 5 6 7 8 9 10 Paul B. Alaback 0 1 2 3 4 5 6 7 8 9 10 David M. Albert 0 1 2 3 4 5 6 7 8 9 10 Colin M. Beier 0 1 2 3 4 5 6 7 8 9 10 Todd J. Brinkman 0 1 2 3 4 5 6 7 8 9 10 Rick T. Edwards 0 1 2 3 4 5 6 7 8 9 10 Eran Hood 0 1 2 3 4 5 6 7 8 9 10 Andy MacKinnon 0 1 2 3 4 5 6 7 8 9 10 Megan V. McPhee 0 1 2 3 4 5 6 7 8 9 10 Trista M. Patterson 0 1 2 3 4 5 6 7 8 9 10 Lowell H. Suring 0 1 2 3 4 5 6 7 8 9 10 David A. Tallmon 0 1 2 3 4 5 6 7 8 9 10 Mark S. Wipfli 0 1 2 3 4 5 6 7 8 9 10 0 M. I. Goldstein U.S. Forest Service , Alaska Region, Juneau, AK 99801 , USA 1 R. T. Edwards U.S. Forest Service, Pacific Northwest Research Station , Juneau, AK 99801 , USA 2 T. J. Brinkman Scenarios Network for Alaska and Arctic Planning, University of Alaska Fairbanks , Fairbanks, AK 99709 , USA 3 C. M. Beier Department of Forest and Natural Resources Management, SUNY College of Environmental Science and Forestry , Syracuse, NY 13210 , USA 4 P. B. Alaback Department of Forest Management, University of Montana , Missoula, MT 59812 , USA 5 T. M. Patterson U.S. Forest Service, Pacific Northwest Research Station , Sitka, AK 99835 , USA 6 M. V. McPhee Fisheries Division, University of Alaska Fairbanks , Juneau, AK 99801 , USA 7 A. MacKinnon British Columbia Forest Service, Coast Forest Region , Victoria, BC , Canada 8 M. S. Wipfli U.S. Geological Survey, Alaska Cooperative Fish and Wildlife Research Unit, Institute of Arctic Biology, University of Alaska Fairbanks , Fairbanks, AK 99775 , USA 9 D. A. Tallmon Biology and Marine Biology Program, University of Alaska Southeast , Juneau, AK 99801 , USA 10 L. H. Suring Northern Ecologic LLC , Suring, WI 54174 , USA We synthesized an expert review of climate change implications for hydroecological and terrestrial ecological systems in the northern coastal temperate rainforest of North America. Our synthesis is based on an analysis of projected temperature, precipitation, and snowfall stratified by eight biogeoclimatic provinces and three vegetation zones. Five IPCC CMIP5 global climate models (GCMs) and two representative concentration pathways (RCPs) are the basis for projections of mean annual temperature increasing from a current average (1961- - 1990) of 3.2 C to 4.96.9 C (5 GCM range; RCP4.5 scenario) or 6.48.7 C (RCP8.5), mean annual precipitation increasing from 3130 mm to 32103400 mm (39 % increase) or 3320 3690 mm (618 % increase), and total precipitation as snow decreasing from 1200 mm to 940720 mm (2240 % decrease) or 720500 mm (4058 % decrease) by the 2080s (2071 2100; 30-year normal period). These projected changes are anticipated to result in a cascade of ecosystem-level effects including: increased frequency of flooding and rain-on-snow events; an elevated snowline and reduced snowpack; changes in the timing and magnitude of stream flow, freshwater thermal regimes, and riverine nutrient exports; shrinking alpine habitats; altitudinal and latitudinal expansion of lowland and subalpine forest types; shifts in suitable habitat boundaries for vegetation and wildlife communities; adverse effects on species with rare ecological niches or limited dispersibility; and shifts in anadromous salmon distribution and productivity. Our collaborative synthesis of potential impacts highlights the coupling of social and ecological systems that characterize the region as well as a number of major information gaps to help guide assessments of future conditions and adaptive capacity. 1 Introduction The northern coastal temperate rainforest of southeastern Alaska and British Columbia is the largest contiguous coastal temperate rainforest in the world, and yet there is limited synthesized information on transboundary climate change implications (Fig. 1). Steep, sloping watersheds where average winter temperatures are within a few degrees of freezing (Simpson et al. 2005), drain the Coast Range into estuaries of the eastern Pacific Ocean. This sharp environmental gradient results in a high degree of climatic sensitivity and changes in ecological communities over relatively short distances, our understanding of which would benefit from increased interdisciplinary collaboration. This paper represents the synthesis efforts of 15 regional resource experts to identify important social and ecological implications in the context of a long-term climate modeling exercise. The governing watershed dynamics in this ecoregion can be grouped into three general categories: glacial melt, snowmelt, or rainfall systems (Edwards et al. 2013; Fig. 2). In lowland forest streams, the annual pattern of watershed discharge tracks the annual pattern of precipitation. These watersheds are predominantly found on island provinces (sections 2, 4, 5, and 6 in Fig. 1). Snowmelt watersheds are characterized by a spring snowmelt peak, a summer discharge minimum and an autumnal flow peak. These watersheds can be found on central Fig. 1 A map of the study area with the eight biogeoclimatic provinces, three vegetation zones, and current habitat totals (ha) for the coastal temperature rainforest of southeast Alaska, USA, and northern coastal British Columbia, Canada Fig. 2 Characteristic hydrographs for the three watershed types (glacial, snowmelt-dominated, and rain-dominated) in the coastal temperate rainforest of southeast Alaska and northern coastal British Columbia. Hydrographs are long term averages (3060 years) from three individual representative streams in southeast Alaska, and are compared with long-term average precipitation in Juneau, Alaska, USA parts of mountainous islands and in mainland provinces (1, 3, 7, and 8). Finally, high-elevation glacial watersheds export little water during winter and early spring, and have their main peak discharge during late spring to early fall. Glacial watersheds are found almost exclusively in mainland provinces (1, 3, and 8). Within this framework, a primary control on the timing and magnitude of stream flow is the proportion of the watershed that lies above the rain-snow transition zone, making the hydrology of this region particularly sensitive to changes in snowline elevation. For instance, water temperatures in rainfall dominated watersheds are 5 12 C warmer during summer than snowmelt and glacial watersheds (Fellman et al. 2014). Although species diversity is low relative to other rainforests globally, ecosystem productivity is extraordinarily high (Alaback 1996). For example, the total carbon stock in the forest and soils of the Tongass National Forest in southeast Alaska is 8 % of that in the conterminous United States (Leighty et al. 2006). Southeast Alaska (Halupka et al. 2003) and northern British Columbia (Temple 2005) contain a combined estimate of 7700 anadromous salmon streams with six Pacific salmonids (Oncorhynchus spp.). In southeast (...truncated)