Restoring Aspen Riparian Stands With Beaver on the Northern Yellowstone Winter Range

Aspen (Populus tremuloides) on the Gardiner Ranger District, Gallatin National Forest, have declined over the last half-century. In an attempt to reverse this trend, beaver (Castor canadensis) were reintroduced in Eagle Creek in 1991. In 2005, we assessed the long-term effects of beaver on aspen stands and the associated riparian area in the Eagle Creek drainage. Aspen recovery was estimated by comparing vegetative changes among control sites with \u3c10 percent beaver use\u3e(n = 5), active beaver sites (n = 6), sites abandoned for 1 to 3 years (n = 7), sites abandoned for 4 to 6 years (n = 4), and sites abandoned for 7 to 11 years (n = 5). Aspen stem densities in active sites and sites abandoned by beaver for 1 to 3 years were similar (2.6/m2) and greater (P = 0.01) than the remaining sites. Sprout and sapling densities were greater (P = 0.01) on active and sites abandoned for 1 to 3 years compared to the other sites. Aspen suckers were not able to grow taller than 2m on sites without beaver activity for 4 to 1 years, which prevented aspen recovery. Beaver activity stimulated the growth of aspen sprouts and saplings, but ungulate herbivory prevented successful aspen recovery in Eagle Creek