Climate change vulnerability and adaptation in the North Cascades region, Washington.

Abstract

The North Cascadia Adaptation Partnership (NCAP) is a science-management partnership consisting of the U.S. Department of Agriculture Forest Service Mount Baker-Snoqualmie and Okanogan-Wenatchee National Forests and Pacific Northwest Research Station; North Cascades National Park Complex; Mount Rainier National Park; and University of Washington Climate Impacts Group. These organizations worked with numerous stakeholders over 2 years to identify climate change issues relevant to resource management in the North Cascades and to find solutions that will facilitate the transition of the diverse ecosystems of this region into a warmer climate. The NCAP provided education, conducted a climate change vulnerability assessment, and developed adaptation options for federal agencies that manage 2.4 million hectares in north-central Washington.In the Pacific Northwest, the current warming trend is expected to continue, with average warming of 2.1 °C by the 2040s and 3.8 °C by the 2080s; precipitation may vary slightly, but the magnitude and direction are uncertain. This warming will have far-reaching effects on aquatic and terrestrial ecosystems. Hydrologic systems will be especially vulnerable as North Cascades watersheds become increasingly rain dominated, rather than snow dominated, resulting in more autumn/winter flooding, higher peak flows, and lower summer flows. This will greatly affect the extensive road network in the North Cascades (longer than 16 000 km), making it difficult to maintain access for recreational users and resource managers. It will also greatly reduce suitable fish habitat, especially as stream temperatures increase above critical thresholds. In forest ecosystems, higher temperatures will increase stress and lower the growth and productivity of lower elevation tree species on both the western and eastern sides of the Cascade crest, although growth of highelevation tree species is expected to increase. Distribution and abundance of plant species may change over the long term, and increased disturbance (wildfire, insects, and invasive species) will cause rapid changes in ecosystem structure and function across broad landscapes, especially on the east side. This in turn will alter habitat for a wide range of animal species by potentially reducing connectivity and latesuccessional forest structure.Coping with and adapting to the effects of an altered climate will become increasingly difficult after the mid-21st century, although adaptation strategies and tactics are available to ease the transition to a warmer climate. For roads and infrastructure, tactics for increasing resistance and resilience to higher peak flows include installing hardened stream crossings, stabilizing streambanks, designing culverts for projected peak flows, and upgrading bridges and increasing their height. For fisheries, tactics for increasing resilience of salmon to altered hydrology and higher stream temperature include restoring stream and floodplain complexity, reducing road density near streams, increasing forest cover to retain snow and decrease snow melt, and identifying and protecting cold-water refugia. For vegetation, tactics for increasing resilience to higher temperature and increased disturbance include accelerating development of late-successional forest conditions by reducing density and diversifying forest structure, managing for future range of variability in structure and species, including invasive species prevention strategies in all projects, and monitoring changes in tree distribution and establishment at tree line. For wildlife, tactics for increasing resilience to altered habitat include increasing diversity of age classes and restoring a patch mosaic, increasing fuel reduction treatments in dry forests, using conservation easements to maintain habitat connectivity, and removing exotic fish species to protect amphibian populations.