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Effects of long-term use by big game and livestock in the Blue Mountains forest ecosystems.Author(s): Larry L. Irwin; John G. Cook; Robert A. Riggs; Jon M. Skovlin
Source: Gen. Tech. Rep. PNW-GTR-325. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 49 p. (Everett, Richard L., assessment team leader; Eastside forest ecosystem health assessment; Hessburg, Paul F., science team leader and tech. ed., Volume III: assessment.)
Publication Series: General Technical Report (GTR)
Station: Pacific Northwest Research Station
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DescriptionThe effects on eastside forest ecosystems from long-term grazing by large mammals are assessed, because long-term herbivory can reduce or increase ecosystem productivity. The assessment emphasizes elk and cattle in the Blue Mountains of northeast Oregon and southeast Washington. Histories of populations of large mammals and their effects in the Blue Mountains are described. Maximum populations of domestic livestock in the Blue Mountains occurred about the turn of the 20th century, declined by 1940, and increased slightly to the present. Livestock grazing on Federal livestock allotments declined from 1915 through 1950, and remained relatively stable since. Elk herds, which existed in relatively low numbers prior to Euroamerican settlement, were decimated by the late 1800s. Hunting restrictions and translocations resulted in increased herds, and hunting was re-instituted in 1927 in Washington and in 1933 in Oregon. Elk herds grew to high density levels by 1980. Long-term heavy use by domestic livestock, primarily cattle, and elk has changed ecosystem processes. There is empirical evidence that persistent herbivory by large mammals caused moderate to severe reduction of shrubs and forage productivity in a variety of logged and unlogged forest communities, with subsequent effects on frequency of wildfire and conifer seedling establishment in some plant communities. Long-term herbivory was shown to have alternative effects by either improving or reducing wood-fiber production by reducing competition from understory plants or reducing soil fertility. The changes in plant communities caused by the herbivores may have had negative feedback effects to productivity of both elk and cattle. Cattle do not achieve desired weight gains on summer allotments. Empirical studies on forage quality and livestock nutritional status support a view that large domestic and wild mammals subsist on suboptimal forage conditions most of the year in the Blue Mountains. Survival of elk calves appears low, partly as a result of density-induced shortages of high-quality forage. The reduced calf production appears to be exacerbated by low adult bull:cow elk ratios, which reduces calf survival via delayed and lengthy birthing periods. The low bull:cow ratios are a result of reduced cover due to logging and increased access to hunters due to logging roads. Reduced big game productivity has led to restrictions on hunting opportunities, with concomitant losses in revenue to local economies. In addition, the dense elk herds, in concert with forest management activities on federal lands, have resulted in increased use by elk on private lands, where they damage crops. The paper identifies adaptive management experiments that could identify options for-clarifying the complex relationships between herbivores, vegetation, and ecosystem processes and identify management options for restoring forest health.
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CitationIrwin, Larry L.; Cook, John G.; Riggs, Robert A.; Skovlin, Jon M. 1994. Effects of long-term use by big game and livestock in the Blue Mountains forest ecosystems. Gen. Tech. Rep. PNW-GTR-325. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 49 p. (Everett, Richard L., assessment team leader; Eastside forest ecosystem health assessment; Hessburg, Paul F., science team leader and tech. ed., Volume III: assessment.)
KeywordsAdaptive management, big game, Blue Mountains, cattle, density-dependence, ecosystem, elk, grazing, herbivory, livestock, nutrient cycling, ungulate
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