Contribution to Book
WD Shepperd, D Binkley, DL Bartos, TJ Stohlgren, and LG Eskew compilers
Sustaining Aspen in Western Landscapes: Symposium Proceedings
USDA Forest Service Rocky Mountain Research Station
Aspen has been declining in the Yellowstone Ecosystem for more than 80 years. Some authors have suggested that aspen is a marginal plant community in Yellowstone and that recent climatic variation has adversely affected aspen, while others contend that excessive browsing by native ungulates is primarily responsible for aspen’s widespread decline. To test these hypotheses, I measured all the long-term aspen exclosures (n = 14) in the Yellowstone Ecosystem. Aspen stands inside all exclosures successfully produced new stems greater than 2 m tall without fire or other disturbance, while few outside stands successfully regenerated due to repeated browsing. Understory species composition was also significantly different inside and outside exclosures. Protected aspen understories were dominated by tall, palatable shrubs and forbs, while grazed understories were dominated by exotic grasses and unpalatable, low-growing forbs. None of the enclosed aspen exhibited any signs of physiological stress, even on dry south-facing hillsides, an indication that climatic variation has not adversely impacted aspen. Instead, exclosure data suggest that aspen has declined throughout the Yellowstone Ecosystem due to repeated browsing by native ungulates, primarily elk.
Kay, CE. 2001. Long-term aspen exclosures in the Yellowstone ecosystem. WD Shepperd et al (compilers). Sustaining Aspen in Western Landscapes: Symposium Proceedings. Proceedings RMRS-P-18. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. Fort Collins, CO.