Bioturbation by grizzly bears in relict solifluction features of Glacier National Park, Montana, USA

Abstract

Grizzly bears are an integral part of the northern Rocky Mountains ecosystem, where their foraging and denning leaves a measurable impact on the landscape. The purpose of this project was to evaluate the erosional effect of grizzly bears on relict solifluction tread and riser environments in the alpine tundra of Glacier National Park, Montana, USA. Grizzly bear excavation sites and material removed from vegetated risers and deposited downslope by bears was classified into either recent or decaying (i.e., not the current season) excavations, measured, and the volume of each excavation was calculated to determine the magnitude of disturbance by grizzly bears in this alpine environment. Grizzly bear activity was found at only one of four sample sites, where grizzlies removed 1.1727 m3 of material (new excavations = 0.6974 m3, old excavations = 0.4754 m3). The width of treads and risers was also measured to determine if there were differences in the dimensions of solifluction features where bear activity was observed. Although one of the study sites did have statistically wider treads and narrower risers than the other study sites, no grizzly bear activity was observed at that site, suggesting that excavations are related to factors intrinsic to solifluction features. A conceptual model of the degradation of turf was developed based on observations of vegetation and soil removed by bears, illustrating how foraging activity in a tread and riser environment may produce micro-scale changes in the landscape over time.

Keywords

• Zoogeomorphology
• Grizzly bears
• Relict Solifluction
• Glacier National Park
• Bioturbation