Paul C. Rogers
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Historical Landscape Ecology of Seral Aspen in the Western U.S.: Examples from the Sierra Nevada and Bear River Ranges
Paul C. Rogers, Utah State University, Logan, UT
Many factors are influencing contemporary aspen stands of the western United States. Whether herbivory, fire, insects, disease, livestock, environmental conditions, or genetic make-up are directly impacting aspen stand health, human actions and climate play disproportionate roles. Examples of historic impacts on aspen at landscape (Utah/Idaho) and regional (California/Nevada) scales present a context for subsequent talks. We will examine predominately seral aspen communities in light of 19th and 20th century land use and climate patterns. In the Sierra Nevada, aspen plays a smaller role, often confined to riparian communities in terms of geographic extent. However, this limited coverage should not imply a minor role in regional biodiversity. While smaller in size, the Bear River range is represented by extensive aspen forests in upland as well as riparian zones. Beyond this initial distinction, historical patterns are strikingly similar between the two areas, although it may be argued the scale of impacts is different. In both areas, during the mid- to late-19th century huge sheep herds grazed in the montane zones, leaving a highly modified landscape. Additionally, a pattern of intense drought late in the 19th century followed by very high moisture in the first two decades of the 20th century was conducive to widespread aspen stand initiation. Large fires set annually by sheep herders cleared competing vegetation and stimulated aspen sprouting. Cessation of settlement burning, implementation of fire suppression, and a century of above average moisture allowed aspen to flourish at first, but later in this period favored succession to shade-tolerant conifers. Are these changes within the ‘natural range of variability?’ Past climate data presented here places this period in the context of aspen stand ages and a much longer (1000 yr.) climate record. Understanding of these patterns may assist managers in altering actions to fit future conditions.