The Role of Postfire Coarse Woody Debris in Aspen Regeneration

Abstract

The paucity of aspen (Populus tremuloides) regeneration in the western United States and on Yellowstone National Park's (YNP) northern range has been of concern to managers and scientists for much of the 20th century, with the effects of ungulate browsing, climate fluctuation, and fire suppression being vigorously debated. We analyzed the interaction of fire and elk (Cervus elaphus) browsing in YNP, specifically the role of coarse woody debris as a mechanism for assisting aspen regeneration. We hypothesized that fallen conifers killed in the 1988 YNP fires would provide refugia, allowing a limited amount of aspen regeneration under the current levels of heavy ungulate browsing. We located burned sites on YNP's northern range and searched for “jackstraw piles,” where fallen conifers provided aspen refugia from ungulate browsing. We discovered that aspen suckers protected by fallen conifer barriers were on average over two times the height of adjacent unprotected suckers. Paired t-tests showed a highly significant difference between the aspen heights within the protected jackstraw sites (>0.8 m high) and those in the open that were subjected to elk browsing (P = 0.000). These results illustrate the role that fallen conifers can play in aspen regeneration as well as the interaction of the ecological processes of wildfire, ungulate browsing, and seral stage development. West. J. Appl. For. 16(2):61–64.