PARENT SESSION
Oral Session - Forests Chair(s): Gustafson, Eric ¹, ¹ Landscape Ecology Unit, Rhinelander, WI
Friday, April 2, 2004 3:00 PM - 5:20 PM Apollo Room 7

Diverse trends of aspen decline in the northern Front Range of Colorado. ^*KASHIAN, DANIEL M. ¹, ROMME, WILLIAM H. ¹ and REGAN, CLAUDIA M. ^1,2, ¹ Department of Forest, Rangeland, and Watershed Stewardship, Fort Collins, CO, USA² Rocky Mountain Region, Lakewood, CO, USA

ABSTRACT- Several investigators have documented a general decline in aspen (Populus tremuloides) forests across the Rocky Mountains, at least at local scales, due to factors such as climate fluctuations, conifer invasion or reduced aspen establishment due to fire suppression, and increased elk browse. However, many studies have failed to describe the diversity of trends in aspen decline, which may have important implications for interpreting landscape-scale conditions of aspen forests. We examined aspen stands in the northern Colorado Front Range to assess the diversity of trends of aspen decline and predict long-term changes in aspen forests across this landscape. Aspen stand structure was highly diverse, but nearly 70% of aspen stands in the study area included ramets 100-140 years old, corresponding to a period of widespread open-range grazing at lower elevations. Elk browse damage to regeneration or to bark was noted in all stands, but was higher at lower elevations (p < 0.05). Although 62% of age distributions indicated declining stands, we noted three specific trends for aspen in the northern Front Range: 1) aspen stands exhibiting age distributions that suggest a self-replacing stand (38% of stands); 2) high-elevation aspen stands seral to conifers, primarily those that decline throughout the fire interval but vigorously re-establish following disturbance (43%); and 3) low-elevation aspen stands declining due to chronic ungulate damage (19%). These results reiterate the importance of a broad-scale approach in assessing aspen decline, but also stress the importance of natural vs. human disturbances in the maintenance or decline of aspen stands in the West.

KEY WORDS: aspen decline, Populus tremuloides, Colorado Front Range, disturbance, succession