Multi-scale habitat selection of elk in response to beetle-killed forest

Abstract

Forests of the Rocky Mountains (USA and Canada) have experienced a large-scale bark-beetle (Dendoctronus ponderosae) epidemic that has led to widespread mortality of pine trees, followed by structural and compositional changes to the forest. The millions of dead trees resulting from this event likely have an effect on ecosystem processes, but currently those effects are mostly unclear. Changes to forest canopy and understory structure are likely to affect behavior and space use of large ungulates as forage abundance, thermal cover, and locomotive costs are presumably altered. We developed and tested hypotheses for how resource selection in summer of female elk (Cervus canadensis; n = 47; 2012–2016), the primary large mammal in our study area, was influenced by changes in canopy, understory vegetation, and downed logs in bark-beetle affected forest in south-central Wyoming, USA. We employed global positioning system (GPS) technology, an imagery-derived land cover classification specifically depicting beetle-affected forest, and on-the-ground forest measurements to develop resource and step selection functions. At the study area scale, elk avoided beetle-killed forest during nearly all parts of the day and selected for intact conifer forest during the day. At the micro-habitat scale, as canopy cover decreased in beetle-killed areas, there was a concomitant increase in grass biomass and downed logs. Nevertheless, while in the forest, elk did not alter resource selection relative to changes in understory vegetation or downed logs. The boost in forage abundance within beetle-killed areas was insufficient to overcome the presumed increases in energy expenditures associated with locomotion and thermoregulation in beetle-killed forests. The bark-beetle epidemic has altered how elk use the landscape and has resulted in a potential loss of forest habitat that elk use during the day. Our results indicate that habitat treatments (i.e., fire or harvest) that remove standing dead trees and downed logs in beetle-killed forest would further facilitate understory growth while reducing the locomotion costs associated with foraging in beetle-killed forest. © 2019 The Wildlife Society.