Effects of long-term use by big game and livestock in the Blue Mountains forest ecosystems.

Abstract

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.

Weather and human impacts on forest fires: 100 years of fire history in two climatic regions of Switzerland

“…This result is only partly in agreement with our hypothesis that increasing livestock densities should be associated with a decreasing fire occurrence due to fuel load removal (cf. Section 2.3), and goes against findings from many studies in North America and Europe (Savage and Swetnam, 1990;Irwin et al, 1994;Heyerdahl et al, 2001;Fry and Stephens, 2006;Kalabokidis et al, 2007). This hypothesis holds for low to moderate livestock densities only, i.e.…”

Dry forests and wildland fires of the inland Northwest USA: Contrasting the landscape ecology of the pre-settlement and modern eras

“…For example, domestic livestock grazing beginning in the 1870s rather abruptly reduced the abundance and distribution of flashy fuels that can rapidly carry surface fires across the landscape (Belsky and Blumenthal, 1997;Belsky et al, 1999;Irwin et al, 1994). In addition, grazing by large populations of deer during the 1940s-1960s, and more recently elk, combined with domestic livestock grazing to remove much of edible shrub cover as well as the flashy fuels (Irwin et al, 1994;Riggs et al, 2000).…”

Annual and decadal climate forcing of historical fire regimes in the interior Pacific Northwest, USA

“…Grazing reduces the herbaceous fuel that carries low-severity res in some mixed conifer forests in the PNW (Rummell, 1951;Zimmerman and Neuenschwander, 1984) and grazing has been implicated in the decline of re occurrence in the SW (Madany and West, 1983;Savage and Swetnam, 1990;Savage, 1991). In the Blue Mountains, Euroamerican settlers increased the number of domestic grazing animals eight-to tenfold in the 1870s-80s and sustained these populations into the mid-twentieth century (Irwin et al, 1994). Consequently, reduced herbaceous fuel loads in the watersheds, or the areas surrounding them, may have persisted well into the twentieth century, lowering the potential for re ignition and/or spread during the dry years of the 1920s-30s.…”

“…Consequently, we believe re extent to be most accurately reconstructed for Dugout because we sampled a larger area there than in the other watersheds. We analysed re-climate relationships for the period 1706-1900 because the climate reconstructions begin in 1706 and there was an obvious change in re extent after 1900 in all watersheds, a period of changing land use in the Blue Mountains (Schwantes, 1989;Irwin et al, 1994;Robbins and Wolf, 1994;Langston, 1995). Before 1900, the time-series of annual re extent in each watershed varied about a constant mean that was 3-7% of the area sampled (Tucannon = 59 ha, Imnaha = 66 ha, Baker = 253 ha, Dugout = 623 ha; Figure 2).…”