Bioturbation by gophers and marmots and its effects on conifer germination

Although climate has been shown to have a considerable influence on alpine forest dynamics, many fine‐scale processes contribute to observable forest patterns. Disturbances created by burrowing mammals may provide conifer seedlings with refuge in previously inhospitable environments and may result in conifer invasion that is not directly associated with climate change. In Olympic National Park, Washington, USA, Olympic marmot (Marmota olympus) populations have declined. Abandoned marmot burrows, which may provide ideal sites for conifer establishment, now dot the alpine landscape. Similarly, in Glacier National Park, Montana, USA, pocket gophers (Thomomys talpoides) have disturbed large areas of alpine meadows at treeline. Field and laboratory analysis of gopher eskers and spoil mounds of abandoned marmot burrows illustrated that such sites are less compacted than soils in adjacent, undisturbed locations. Additionally, disturbed soils contained higher amounts of phosphorus and lower amounts of potassium and organic matter. Soils disturbed by gophers were cooler at the surface and warmer at depth than undisturbed soils, whereas marmot‐disturbed soils were warmer at the surface and cooler at depth. Experimental seed germination of subalpine fir (Abies lasiocarpa) was higher on mammal‐disturbed soils, and this was statistically significant for marmot‐disturbed soils. These findings suggest that fossorial mammal disturbances have the potential to affect conifer germination and establishment. Furthermore, this research initiates the dialogue for future research on the distinct morphological and behavioral influences of different fossorial mammals as zoogeomorphic agents and ecosystem engineers. Copyright © 2016 John Wiley & Sons, Ltd.