ISSUE PRIMER

DETAILED REPORT

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Olympic National Park

A spectacular outpost of varied habitats on the Olympic Peninsula, Olympic National Park represents Washington State's premier wilderness area. Roughly half the world's temperate rainforest is in the Pacific Northwest, and several magnificent tracts are found within the nearly one million acres that make up the park. Some of North America's largest and most spectacular coniferous tree species are heavily represented in the park, including the western red cedar, western hemlock, Sitka spruce, and and the giant Douglas fir. These trees can take centuries to reach maturity and may live longer than 1,000 years. Olympic National Park is critical for the preservation of large areas of old-growth forest because so many other forests are subject to active or potential logging operations. Old-growth forest is especially important for species such as the Roosevelt elk, spotted owl, marbled murrelet, Olympic salamander, banana slug, Pacific rhododendron, and sword fern. At higher elevations than the rainforest, the park supports subalpine forest, and, higher still, beautiful subalpine and alpine meadows that come alive with wildflowers in the spring and early summer. These mountain habitats are likely to be at greatest risk from climate change.

Recent research from Olympic National Park and from Mount Rainier National Park farther to the east shows that the warming climate has favored the steady invasion of subalpine meadows by subalpine forest (Rochefort et al. 1994). There is good evidence that this trend is strengthening as the modern-day rate of greenhouse warming increases. At Mount Rainier National Park, the wildflower meadows are the prime attraction for most of the more than 2 million vistors received annually. The gradual diminution of the area of wildflower-rich grasslands is a strong probability with global warming, as it is for the meadows of Olympic National Park (Peterson 1994). Scientists predict that under all likely global warming scenarios, trees will invade subalpine flower meadows (Zolbrod and Peterson in press). Warming is not the only factor involved here though. Precipitation regime and winter snowpack may prove critical in determining eventual changes in these high elevation forests.

Climate research in Olympic National Park and Mount Rainier National Park has recently established that high-elevation forest will react differently from lowland forest in response to global warming. Even the different types of montane forest will have differing responses. These studies demonstrate the difficulty of making broad-brush predictions of climate impacts even for one National Park without taking into acount the varying ecological changes that will occur in different habitats. Olympic National Park is especially interesting in that the forests of the southwestern region are subject to extremely high levels of precipitation while those in the northeast exist under much drier conditions. These latter areas are dominated by subalpine fir forests and grass-sedge meadows. The wet, southwestern forests of the Olympic Mountains are dominated by mountain hemlock and ericaceous meadows. The research shows that for most subalpine tree species at many locations, winter precipitation is a critical limiting factor for growth. In addition, longer growing seasons (e.g., warmer springs) can improve growth, and hotter summers and drought conditions inhibit it (Peterson 1994).

According to climate and vegetation models, the drier, northeastern forests may be the most sensitive to both temperature and precipitation change. Over time, and given a warmer, drier climate, drought-tolerant species would become established lower down the mountainsides, the northern slopes being dominated by subalpine fir and the southern slopes by lodgepole pine. In the southwestern region, it is predicted that a warmer climate will push dominant tree species several hundred meters higher in elevation, with subalpine meadows and mountain hemlock forests being replaced by Pacific silver fir (Zolbrod and Peterson in press). Observations in Olympic National Park today show that changes are already occurring at the tree line, with forest species beginning to crowd the edge of the meadows and fill the gaps of open grassland (Peterson pers. com.). Much farther south, research on the tree line forests of Sequoia National Park of California's Sierra Nevada mountains has shown that drought may limit the ability of tree line to move upslope, even when temperatures are warming (Lloyd and Graumlich 1997). These studies show that while upward tree line change occurs very slowly, there can be relatively rapid changes in the density of forest at the ecotone and distribution of individual species.In many places, soil conditions will limit the ability of tree species to shift distribution with changing climate.

Other potential impacts of climate change on the protected areas and federal lands of the Pacific Northwest are likely to include glacier melt and changes in fire regime. In 1994, the National Biological Survey (NBS) identified the glaciers of Olympic National Park, Mount Rainier National Park, and North Cascades National Park as potential indicators of global warming (see also Glacier National Park). Glaciers of the Pacific Northwest are expected to be especially sensitive to climate change because of their low elevation and small size (NBS in litt.). Vulnerability of westside forests to fire is likely to increase under a warmer, drier climate, and potential decreases in humidity or precipitation, higher frequency of easterly winds or lightning storms, or more frequent drought would heighten the risk. Outbreaks of defoliating attacks by western spruce budworms could occur more frequently and become much more damaging for westside conifer forests (which have no natural chemical defenses) under certain climate scenarios (Norse 1990).