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2013 Abstracts

Facilitative and Competitive Interactions in Subalpine Aspen-Fir Forests

Jason Bartholomew, Brigham Young University

Plant and Wildlife Sciences

After disturbances in plant communities (i.e. wildfire), there is a natural succession of plants in which plants colonize the empty area and are gradually replaced by more competitive species. In subalpine forests, the principle colonizers after wildfire are quaking aspen (Populous tremuloides) which are later replaced by subalpine fir (Abies lasiocarpa). It has been shown that aspen facilitate, or enable, the establishment of subalpine fir at their base. This study examines the aspen-subalpine fir interaction in order to better understand the dynamics of the shift from aspen to fir dominance. It is hypothesized that the fir in a facilitated pair eventually exerts a competitive influence on the aspen resulting in a decrease in aspen fitness. The growth rates of the two species were examined in different stand types (aspen, mixed and subalpine fir), as independent trees or in facilitated pairs, and in three separate size classes. Samples were collected by taking a core sample or cross-section from trees within the categories listed above. The age and annual growth rings were measured with a measuring stage. The annual growth rings were used to calculate basal area increase (BAI) which was used to determine growth rates. The results suggest the growth rate of aspen in facilitated pairs decreases as firs mature thereby decreasing fitness within the aspen population due to competitive influences from facilitated firs. This may explain the mechanism for the successional shift that can significantly impact indigenous animal populations and local fire cycles.