Climate Impacts on Yellowstone National Park - Research Paper Example

CLIMATE IMPACTS ON YELLOWSTONE NATIONAL PARK Introduction Yellowstone National Park (YNP) is an 8,991 sq km protected area that lies within the Greater Yellowstone Ecosystem in the interior of the North American continent (Gardner et al, 1996). Most of it is within the jurisdiction of the state of Wyoming but its northern part is shared by Montana and Idaho. Elevations within the YNP range from 1600 m in the north where the Yellowstone River flows into Montana to mountain peaks that reach more than 3,000 m along park’s boundaries to the north and east. The YNP straddles the continental divide which marks the collision point of the Atlantic and Pacific continental plates, accounting for the geological and seismological activity of the area (Pritchard, 1999). YNP sits atop a geological mantle plume where the molten magma comes close to the surface which is why boiling mud pots, thermal pools, geysers, a volcanic caldera, ancient lava flows, and eroding rivers and waterfalls continues to characterize the park. In fact, it was for these that the park was declared a protected area in 1872 – biodiversity conservation was only an afterthought. Expectedly, the landscape pattern of YNP is complex but geologic factors had to do with only a part of that. Other interacting influences such as climate, geology, soils, hydrology, terrain, and vegetation, and human impacts determine the changes in the physical environment (Garrott et al, 2009). Owing to the park’s elevation range, there are also pronounced gradients of temperature and moisture (Romme & Knight, 1982). These abiotic factors in turn influence the ecological processes that make YNP along with the Greater Yellowstone Ecosystem the largest tract of intact natural ecosystem in the north temperate zone (Schullery, 2004). Landscape diversity is the result of two vegetation patterns superimposed on each other: one is the pattern influenced by limiting factors and the other is influenced by patterns of disturbance and recovery within communities (Romme & Knight, 1982). Climate is one such physical limiting factor that dictates the presence, absence and abundance of certain faunal and floral species in a given eco-region. Specifically for the YNP, the last 10,000 or so years have been important in shaping the YNP that is known today (Committee on Ungulate Management in Yellowstone National Park [CUM-YNP], 2002). Patterns of disturbance and recovery (such as geologic and volcanic activities) have contributed to shaping the diversity within YNP and one such recurring event – fire – is also influenced by climate to a certain degree (Swetnam & Betancourt, 1998). Climate Because it is located within the continental North America and exhibits varying elevation gradients, the weather in the YNP is characterized by extremes and fluctuations (Zelt et al, 1999). Climate in the YNP is often cold and moist in higher elevations and temperate and semiarid in the plains. The seasonal climate regimens are due to the interaction between air masses that originate from the Gulf of Mexico, the northern Pacific Ocean, and the Arctic regions. The Gulf air dominates during spring and early summer, while Arctic air blows in during winter. Temperature range could also be extreme: -40°C during the winter to 38°C during the summer (Zelt et al, 1999). Mean annual temperatures range between less than 0°C at Yellowstone Lake to about 10°C in the Montana valley. The coldest month is January with average daily lows that range from less than -18°C in higher elevations to about -8°C in lower plains while July is generally the warmest month, with average daily highs ranging from about 22°C in higher elevations to about 32°C in some valleys. Mountain ranges experience an average frost-free period of less than 10 days while plains experience frost-free periods of up to 140 days. In some sites, climate is cold enough to form permafrost even at elevations as low as 2,400. Evaporation and precipitation distinguish the moist, mountain forest ecosystem from the drier lower-elevation regions where more moisture is evaporated than precipitates (Marston & Anderson, 1991). Most precipitation – about 40 to 45 percent of the annual volume – falls between April and June but the seasonality is not exhibited in mountainous areas. Mean annual precipitation ranges from about 380 mm near Mammoth Hot Springs to more than 2,000mm of the southwest plateaus. A substantial part of annual precipitation is in the form of snowfall, and which varies strongly with elevation. In mountainous terrain, most of the spatial variation in precipitation is explained by the rain-shadow effects of the terrain features (Zelt et al, 1999). The rate of evaporation, on the other hand, depends on temperature, which, in turn, varies with elevation (Zelt et al, 1999). Evaporation is highest where there are strong winds particularly in basins and prairies and lowest in the cool, cloud-shrouded mountaintops. Climate and geomorphology The Pinedale glaciation – the last major Ice Age – started sometime between 25 to 50 thousand years ago and ended until just over ten thousand years ago (Garrott et al, 2009). During its peak around 14,000 years before the present (ybp), glacial ice covered large areas of North America, building up to a thickness of about 1.6 km. Although the continental glaciers did not penetrate farther than the Canada-Montana border, glaciers formed in the mountains of the Greater Yellowstone Ecosystem and have spread to lower elevations to join with the Yellowstone Ice Cap (CUM-YNP, 2002). Consequences of this glaciation have been responsible for shaping much of the dominant landforms still present at the YNP today by redistributing soils and sediments, widening valley bottoms, and blocking streams to form large lakes (Garrott et al, 2009). The Hayden Valley’s hummocky terrain, for instance, is the result of accumulated rocky glacial debris in the ice cap which was covered by lake sediments when ice dam formed at the head of the Grand Canyon of the Yellowstone. As climate became warmer and the ice began to thaw, the ice dam burst, and the resulting floodwaters enlarged the canyon. The influence of these glacial processes continues up to the present day. Headwaters of some streams originate from the glaciers (Garrott et al, 2009). Although many factors influence the flow of streams, along the way they are also fed by precipitation. The contribution of snowmelt to stream flow is actually higher than that of rainfall (CUM-YNP, 2002). Decadal climatic changes such as the El Niño Southern Oscillation (ENSO) phenomena also influence precipitation patterns; specifically, YNP experiences increased precipitation during an ENSO great enough to cause changes to stream courses. The greatest stream-course changes were observed during the flood years of 1996 and 1997 primarily as the result of flood flows (CUM-YNP, 2002). Climate and the Biota Geologic events – with the assistance of climate – may have shaped much of the landforms that are evident in YNP today but climate is much more important in shaping the biota. This is one of the major physical factors that limit the survival of certain floral and faunal species. Specifically, seasonal extremes in temperature or moisture and not their mean annual values are very important for determining the distribution of the organisms in the region. During winter, however, geothermal influences offset the effects of local snow pack and nearby rivers and streams remain ice-free throughout the year thereby allowing plants to grow through winter and providing forage for wintering wildlife (Despain, 1990). Vegetation Deglaciation started around 13,000 to 14,000 ybp and sagebrush is the dominant vegetation in the subalpine forest zone. As glacial ice continued to thaw and retreat, spruce began to colonize the area around 11,500 ybp (Taylor et al, 1997). This was soon followed by lodgepole pine, Douglas fir, and whitebark pine as the climate continued to get warmer, wetter, and more stable. By 4,500 ybp, lodgepole pine dominated the forests with trace amounts of Douglas fir. Both are still the dominant vegetations in the forests that cover 83% of the YNP today, especially at lower elevations (Despain, 1990). Vegetation varies according to the elevation at which it is found because of the varying climates found at different elevations. Generally, climate is cooler at higher elevations and precipitation is also higher and less seasonal than in valleys. The upper timberline is near 3000m and most of YNP lies between 2000 and 2700m in the subalpine zone (Despain, 1990). The vegetation at montane zones below the subalpine zone is characterized by open sagebrush parks on drier areas while mesic locations support alternating stands of Douglas fir and ponderosa pine, with the pines dominating on drier, more exposed slopes (Bailey, 1995). On the subalpine plateaus, upland coniferous forests of lodgepole pine, subalpine fir, Engelmann spruce, and whitebark pine, are more extensive. Above the subalpine forest are the alpine meadows occurring at above 3100 elevation (Despain, 1990). In the alpine meadows, tundra vegetation such as forbs, grasses, sedges, dwarf willows, and prostrate shrubs dominate and trees are either absent or stunted. This distribution pattern have been relatively stable during the last 5000 years as indicated by pollen analysis of pond sediments (Romme & Knight, 1982) Fauna When the glaciers from the last major Ice Age first retreated from the Yellowstone plain, there were mammals other than those found today at the park. Along with the herbivores (elk, mule deer, bison, moose, bighorn sheep, pronghorn, and white-tailed deer) and the native large predators (grizzly bear, black bear, coyote, mountain lion, and the reintroduced gray wolf), there were also mammoths, bighorn bison, horses, camels and other small herbivores, pursued by dire wolves, Pleitocene lions, saber-toothed cats, short-faced bears, among other carnivores (Schullery, 2004). The cause remains much debated (although over-hunting by humans have been cited as one reason) but many of the large mammals such as horses, camels, mammoths became extinct. Other mammals such as the caribou, lemmings, and musk ox retreated to the north at the end of the Wisconsin glaciation about 10,000 ybp due to the changing climate. Climate also influenced the movement of migrating species; that is, winters limit food availability and influence habitat selection thus, animals must move to places where both can be found (Garrott et al, 2009). The northern elk for example has made the northern range of YNP their wintering area while migratory central bison herd – which favors meadow vegetation during winter – defines the central range as theirs. This central range also includes the range of the non-migratory elk herd that occupies the headwater drainages of the Madison River along the western edge of the park; elks are more generalists and can occupy both forests and meadows. During summer, the central migratory bison move to the high elevation Pelican and Hayden valleys in east central Yellowstone. Humans Evidences of human settlement in YNP have been traced to as far back as 11,000 ybp (Schullery, 2004). As soon as the ice retreated and enough plants and animals thrived, humans soon followed. The volcanic activity of Yellowstone provided abundant sources for excellent obsidian, a stone which early Native Americans worked into blades, weapon points and ornaments. Climate dictated where their settlements are located. From the evidence gathered, they hunted the high country for ungulates and smaller animals as well as a variety of plants during summer; during winter, they made more permanent camps at lower elevations and continued hunting on their winter range. There was increased human presence in Yellowstone in the last 1500 years and this may have been due to the increasing population in Northern America as well as the significant increase in available food such as elk (Schullery, 2004). When the Little Ice Age advanced into the Yellowstone in the last three to four centuries before 1850, the impacts it had on human activities could be imagined but research has not been able to fully demonstrate this. When the park was declared a protected area in 1872, it was just coming out of the Little Ice Age but generally, population grew because of the abundance of natural resources which was in turn due to favorable climatic conditions. Climate and Fire As mentioned earlier, physical limiting factors contribute to the distribution patterns of vegetation (which in turn dictates the distribution of faunal species). Another influencing factor to vegetation distribution is the pattern of disturbance and recovery. In YNP, such a disturbance included the recurrent fire; when trees are burned, it restart a long successional process wherein pioneer vegetation communities colonize the burned area and progresses gradually through a series of plant communities towards the climax community (Despain, 1990). Climate plays an important role in fire frequency and extent. In the 20th century specifically, most of the large North American fires were associated with persistent high-pressure ridges or dry La Niña phases of ENSO (Swetnam & Betancourt 1998). In Yellowstone, no large fires occurred during the twentieth century until those of 1988. The fires of 1988 were also the largest since the park’s establishment, affecting more than 3,210 sq km in YNP and the surrounding area which was approximately 36% of the park (Schullery 2004). The magnitude and extent of the fires were primarily due to the unusually prolonged drought and high winds (Bessie and Johnson 1995). Balling, Meyer, and Well (1992) predict that warmer conditions in YNP will more likely, with the probability of summer and autumn drought increasing, make weather conditions for large fires more probable. Their recent analysis of 1895-1989 weather records for YNP revealed a trend wherein summer temperature is generally increasing while spring precipitation has declined; consequently, variations in burn area have been significantly related to those changes. Conclusion The interrelationships between abiotic and biotic factors are extremely complex especially for an eco-region that is as expansive as the Yellowstone Natural Park. There are many interactions that influence the distribution patterns that have been observed through time in the park but climate is a major influence and can thus be generalized. As we have seen, vegetation responded to climatic changes throughout the centuries, only becoming more established in the last 5,000 years. Their stable distribution in the YNP is a factor of elevation gradient – itself influenced by the changing climate as one moves towards higher elevations. The particular temperature and moisture at a given elevation are limiting factors for plants and are the reasons why different species dominate in different elevations. Vegetation, on the other hand, dictates the distribution of faunal species; that is, animals go where there is food and shelter to be had. Climate is also a driver for the migration of animals; specifically, winter limits the availability of forage and they must go where they can have it. Humans, too, mimic this movement of animals until more permanent settlements became possible. Still, it is generally the pattern for human settlements to congregate where food is abundant and the climate is less subject to extreme fluctuations. BIBLIOGRAPHY Bailey, R.G. (1995). Description of the ecoregions of the United States (2d ed.). US: Department of Agriculture, Forest Service Miscellaneous Publication 1391 Balling, R.C.., Meyer, G.A. and Wells, S.G. (1992) Climate change in Yellowstone National Park: is the drought-related risk of wildfires increasing? Climatic Change 22, 35-45. Bessie, W.C., and Johnson, E.A. (1995). The relative importance of fuels and weather on fire behavior in subalpine forests. Ecology 76 (3): 747-762. Committee on Ungulate Management in Yellowstone National Park, National Research Council. (2002). Ecological Dynamics on Yellowstone’s Northern Range. Washington, DC: National Academy Press Despain, D.G. (1990). 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