Oral Session # 93: Vegetation Change and Response.
Presiding: B Parry Hecht
Friday, August 8. 8:30 AM to 12:00 PM, SITCC Meeting Room 105.

The persistence of quaking aspen (Populus tremuloides) in west-central Colorado.

Kulakowski, Dominik*,1, Veblen, Thomas1, 1 University of Colorado - Boulder, Boulder, CO

ABSTRACT- Quaking aspen may be the most important deciduous tree in the subalpine forests of the Rocky Mountains. There has been substantial concern that aspen has been declining during the 20th century in the western landscape due to conifer encroachment associated with fire suppression, as well as other causes. We used a Geographic Information System to compare an 1898 map of vegetation and fires of the Battlement Mesa Forest Reserve, Colorado to a modern map of present forest cover types in order to assess long-term changes in extent of quaking aspen. Based on this comparison, a larger portion of the current landscape is dominated by quaking aspen relative to the late 19th century, before extensive burning in this area. During this time period aspen was persistent over most of its extent, even in the absence of fire. Fires of the late 19th century also increased aspen cover in stands that were previously dominated by spruce and fir. The increase in aspen cover occurred primarily at lower elevations. At higher elevations, where the life history traits of spruce and fir are favored, aspen has been replaced by the conifers in a limited area. However, the total area where spruce and fir have replaced aspen is small in comparison to the area where aspen has increased or has persisted. These findings suggest that the net effect of large severe disturbances during and after the late 19th century increased aspen cover in the Battlement Mesa area relative to the reference period that preceded these disturbances. Where the successional replacement of aspen by conifers is occurring today, such a trend may be a return to conditions more typical of the reference period, prior to Euro-American settlement. The long intervals between natural disturbances in these ecosystems result in a broad amplitude of natural ecological patterns.

Key words: reference conditions, historic range of variability, fire, Populus tremuloides