Aspen Bibliography

Condition and trend of aspen communities on BLM administered lands in central Nevada with recommendations for management

C E. Kay

Document Type

Report

Source

Bureau of Land Management, Battle Mountian, Nevada, 152 pp.

Publication Date

2001

Abstract

Aspen is of special concern in the West because the species does not commonly grow from seed due to its demanding seed-bed requirements. It is thought that environmental conditions have not been conducive to seedling growth and clonal establishment since shortly after the glaciers retreated 10,000 or more years ago. Hence, aspen clones found in central Nevada today have likely maintained their presence on those sites for thousands of years via vegetative regeneration; i.e. root sprouting. In addition, aspen communities support an array of other species and have the highest biodiversity of any upland forest type in the West. This is especially true in central Nevada where many aspen stands are associated with riparian communities. Aspen, though, has been declining in Nevada and throughout the Intermountain West since shortly after European settlement. The reasons for this have been attributed to climatic change, fire suppression, normal plant succession, wild ungulate browsing, and/or grazing by domestic livestock.

To test these hypotheses and to determine the status of aspen on BLM administered lands in central Nevada, I measured 126 representative aspen stands in the Shoshone, Simpson Park, Diamond, Toiyabe, Desatoya, and Roberts Mountains. I also measured all long-term aspen-containing exclosures in those mountain ranges. The exclosures were originally built to study the effect of livestock and/or wildlife use, but because the general climate is the same inside and outside the fenced plots, the exclosures can also be used to evaluate the climatic change hypothesis.

Many aspen stands in central Nevada have not produced new stems greater than 2 m (6 ft) tall in more than 100 years and many stands are in very poor condition. The status and trend of aspen communities in central Nevada, however, is not related to climatic variation, fire suppression, forest succession, or browsing by mule deer. Instead, the condition of individual aspen communities is related to past and present levels of livestock grazing. That is, aspen is declining throughout most of central Nevada due to repeated browsing of aspen suckers by cattle and/or domestic sheep - - repeated browsing eliminates sucker height growth, which prevents their growth into aspen saplings and trees. Without stem replacement, aspen clones are consigned to extinction.

This cause and effect relationship is most clearly demonstrated inside and outside exclosures. In all cases where it was protected, aspen successfully regenerated without fire or other disturbance and developed multi, stem-aged stands, while on adjacent, outside plots, aspen continued to decline. Aspen in central Nevada also experienced major regeneration events on allotments where livestock grazing was temporarily reduced or where BLM had mandated season of use changes. On some allotments, a change from season-long grazing to only early-season grazing, was enough in and of itself, without any reductions in animal unit months (AUMs), to allow aspen to successfully regenerate.

Thus, to reverse the decline of aspen in central Nevada it will be necessary to more closely manage livestock use. Depending on individual sites and the present condition of aspen, it may be necessary to fence some stands and/or restrict livestock to only early-season grazing. If aspen does not respond to those measures, however, it may be necessary to reduce AUM numbers on some allotments. It is also recommended that BLM establish permanent monitoring plots in representative aspen communities throughout central Nevada to evaluate management decisions related to that species.

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