Ecological Dynamics on Yellowstone's Northern Range (2002) / Chapter Skim
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2 Historical Perspective: Yellowstone's Changing Environments
2 Historical Perspective: Yellowstone's Changing Environments
Pages 32-42
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From page 32... ...
SCALES OF CHANGE On a geological time scale, earth's history is one of continuous change driven primarily by plate tectonics, with periodic extraplanetary influences, such as asteroid impacts and solar cycles. On this scale, the earth is fractured; subducted; uplifted; built up by volcanism and sedimentation; and worn away by ice, water, wind, heat, and gravity.
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From page 33... ...
The North American plate is thought to have moved to the southwest, leaving a series of volcanic traces from southwestern Idaho along the Snake River to the currently active Yellowstone region. Geomorpholog~cal changes have not stopped, for uplifting is continuing (Reilinger 19851.
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From page 34... ...
Because the GYE is an "ecosystem island" within a larger human-dom~nated landscape, it is too small to accommodate environmental changes of the magnitude and frequency that were characteristic of the middle Holocene and late Pleistocene without changes in community composition, including local extinctions, greater than those seen during the past 4,000 years. Changes in the late Quaternary (from about 14,000 YBP)
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From page 35... ...
At sites within the GYE, however, most bone beds associated with human hunting contain fewer than five individual animals (Cannon 19921. Unlike bison, no massive bone beds of elk have been found associated with cultural materials, and there is no evidence of artificial elk traps or communal procurement practices like those used for bison (Frison and Bradley 19911.
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From page 36... ...
Glaciation: IS,000 YBP At the peak of the last major glacial period about 14,000 YBP, large areas of North America were covered by glacial ice that had built up to a thickness of about I.6 km over the previous 100,000 years. The continental glaciers penetrated only to the Canada-Montana border, but glaciers formed in the mountains of the GYE and spread to lower elevations and coalesced into the Yellowstone Ice Cap.
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From page 37... ...
. Fire in Yellowstone and the Northern Range Recurrent wildfire profoundly influences fauna, flora, and ecological processes in the northern Rocky Mountains (Habeck and Mutch 1973; Houston 1973; Loope and Gruell 1973; Taylor 1973; Wright and Heinselman 1973; Wright 1974; Arno 1980; Romme and Knight 1981, 1982; Romme 1982; Knight 1987, 1996; Romme and Despain 1989; Despain 1990; Turner et al.
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From page 38... ...
On the northern range, tree-ring evidence and fire scar data indicate that ~ to 10 extensive fires occurred in the area during the last 300 to 400 years, which suggests that fires burned the winter range at intervals of 20 to 30 years before European settlement (Houston 1973, Barrett 19941. Climate plays an important role in fire frequency and extent.
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From page 39... ...
(1992) proposed an idealized scenario to explain how wet periods during the Holocene created widened and sinuous stream beds, and dry periods with burns led to erosion of steeper slopes and aggradation of alluvial fans and incised stream courses.
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From page 40... ...
Stream Flow and Channel Morphology Although many factors influence runoff, typically there is a strong positive correlation between precipitation and stream flow. No long-term trend in stream flow at the Corwin Springs gage on the Yellowstone River just north of the park is apparent through the 91-year record from 1908 to 1999 (p = 0.259~.
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From page 41... ...
They concluded that their "investigation of the sedimentary record does not support the hypothesis that ungulate grazing has had a strong direct or indirect effect on the vegetation and soil stability in the lake catchments or on the water quality of the lakes." A review of their data, however, shows many, but not all, lakes with increasing sediment accumulation starting after the beginning of the twentieth century. Most of the study lakes near the confluence area of the Yellowstone River, Lamar River, and Slough Creek showed sediment increases.
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From page 42... ...
In winter they migrated to lower and warmer regions outside the park area until settlements of farmers in the country surrounding the park made it impossible for them to use their long used winter homes." All these factors fragment habitat and impede ungulate movements and access to foraging areas. This alteration of the landscape outside of YNP may have as great a potential to affect ungulate populations, their behavior, and the use of vegetation as do changing climatic conditions end reintroduction of wolves.
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