Carved out from 2 million acres of pristine Wyoming, Montana, and Idaho lands in 1872 (and celebrating its 125th anniversary in 1997), Yellowstone became the world's first National Park, and is now probably the most famous of all. With its intact grizzly bear habitat and rangelands for buffalo, elk ,and moose, along with spectacular hot springs and geysers, Yellowstone has a wealth of interest to captivate its millions of visitors every year. Connected to Grand Teton National Park in the south and surrounded by National Forest areas such as Shoshone National Forest and Gallatin National Forest, Yellowstone is large enough to be somewhat buffered from external environmental influences. It still suffers, however, from many problems. Visitor pressure is particularly high near roads and the most popular hiking trails and view-points, and environmentalists are constantly fighting threats of mining activities and other developments just outside the park's borders. Moreover, despite the size of the park area, grizzlies and wolves (the latter having been reintroduced in small numbers very recently) often range outside and are occasionally shot by local ranchers.
Since the massive fires of 1988, when nearly half the park was burned to some degree, scientists have been paying greater attention to the possible threat from climate change. Although wildfires are a natural and necessary part of the ecology of western forests, global warming is expected to change their impacts on ecosystems. Climate is not the only factor affecting fires in National Parks. Years of management policy aimed at suppressing natural fires have led to a build-up of flammable material in forests, thus increasing the likelihood of bigger, more intense fires. Also, in a completely natural ecosystem, lightning strikes would be the normal trigger for a fire, but now humans have added campfires and deliberate arson to the potential causes.
Experts agree that the fires of 1988 came about as result of a combination of factors. They included a series of winter drought years (low snowfall) culminating in a hot, dry summer with unusually strong winds unaccompaied by rainfall (Knight 1991, Varley and Schullery 1991). Also important was the fact that lodgepole pine hardly ever burns if stands are less than 150 years old, but by 1988 large areas of the park consisted of lodgepole forest of this age. Under normal conditions, large fires like those of 1988 occur only once in every few generations. But with approximately 40% of the park remaining vulnerable to future large-scale burns, any major increase in fire risk due to climate change would pose a significant problem for Yellowstone (John Varley, pers. com.).
Analysis of historical climate trends in Yellowstone National Park has revealed a significant trend toward conditions that increase the hazard of wildfire (Balling et al. 1992). These studies have shown that fire season (summer) temperatures are increasing and that precipitation is decreasing C even trending toward increased drought probability C in the presummer period of January to June. These factors, along with summer drought stress and wind conditions, are among the most important in determining natural fire risk. The temperature increases recorded in Yellowstone are consistent with those predicted by global change computer simulations.
If the current warming and drying climate trends in Yellowstone continue, then an increased frequency of massive, stand-replacing fires might be expected. This in turn would lead to a replacement of old-growth forest stands by younger age-classes of tree, and a reduction in this habitat could cause local extinction of old-growth forest species such as northern twinflower, fairy slipper, pine martin, and goshawk (Romme and Turner 1990). Loss of old-growth habitat to fire would be compounded by losses due to a general reduction in forest area as a result of global warming and logging activities in important buffer areas outside the park.
Ecologists William Romme and Monica Turner have speculated about what the most significant consequences of various climate scenarios would be for the Greater Yellowstone Ecosystem, of which Yellowstone National Park is a major component. Under all three scenarios they examined, the most significant and negative impacts could occur in the high montane whitebark pine forest and in the alpine zone (Romme and Turner 1990). In Romme and Turner's study, a warmer wetter climate appears preferable to a warmer drier climate for the park, mainly due to increased fire risk in the drier scenario. Unfortunately, today's actual climate trends point toward the more damaging dry scenario. If this situation continues, up to 90% of the habitat suitable for whitebark pine in Yellowstone could disappear within 50 years. The whitebark pine nuts and army cutworm moth caterpillars found in these forests both provide vital food for Yellowstone's grizzly bear population (Matson and Reid 1991). However, grizzlies are famously flexible when it comes to food and they may be able to adapt to the loss of certain food sources by finding alternatives (John Varley pres.com.).
Whitebark pine forest may be replaced with Douglas fir, and on the lower slopes, forest would most likely give way to treeless landscapes dominated by big sagebrush, Idaho fescue, and bluebunch wheatgrass. Local extinctions of alpine species can be expected as a result of loss of some habitat and increased fragmentation of the remainder (Romme and Turner 1990). However, palaeoecological studies in Yellowstone National Park and Grand Teton National Park show that the tree line has changed little in response to past climate change, but that changes in species distribution and abundance have been quite large. Long-term decrease in snowpack would be the most important factor in causing an upslope movement of the tree line (Peterson in litt.). The most likely impacts on high-elevation habitats will be a re-mixing of the flora and fauna that make up these ecosystems, and perhaps the creation of new communities of species with different plants gaining dominance.