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.

Hiding Without Cover? Defining Elk Security in a Beetle‐Killed Forest

“…An additional consideration in interpretations and applications of our work was the successional stage of pine beetle‐infested forests in our study area. An increase in fallen trees is presumed to influence wildlife mobility in pine beetle‐infested forests with a hypothesized reduction in use associated with increased costs in mobility (Saab et al , Lamont et al ). Our study occurred between 2015 and 2017, 7–10 years after the peak of the pine beetle infestation in 2008, yet most of the infested trees were standing dead.…”

Bark Beetle‐Affected Forests Provide Elk Only a Marginal Refuge from Hunters

“…As the beetle‐kill epidemic unfolds, a subsequent increase in downed trees and understory vegetation could influence hunter and elk movements differently than what we observed. Additionally, although our land classification model was generally predictive, error in prediction associated with beetle‐kill likely affected our results to some degree (Lamont et al ). We doubt, however, that any classification errors were sufficient to bias our habitat selection analyses.…”

“…We suspect elk use of beetle‐kill may offer a perceived refuge (Mysterud and Østbye , Thurfjell et al ) while simultaneously increase foraging opportunities (Pec et al ), which may thus reduce the tradeoff associated with seeking refuge at the cost of access to forage. Although recent researchers in the same study area did not report that increases in understory in beetle‐kill resulted in increased use of these areas by elk (Lamont et al ), this work was explicitly focused on summer (Jun–Aug), and it may be that when elk are faced with hunting pressure they use this novel forage resource while attempting to reduce exposure to hunters (Lone et al ).…”

“…More recently, starting in the late 1990s, an unprecedented bark‐beetle epidemic occurred that killed 60–80% of the lodgepole pine, and to a lesser extent, Engelmann spruce (Raffa et al , Kayes and Tinker , Black et al ). This event dramatically changed the structure and characteristics of conifer forests within the study area (Klutsch et al , Collins et al , Pec et al , Lamont et al ).…”

“…Nevertheless, as elk populations across the West have grown (Johnson et al , O'Gara and Dundas ), wildlife agencies have struggled to obtain sufficient harvest of adult females to regulate elk herds that seek refuge on private lands with little hunter access (Burcham et al , Vieira et al , Brodie et al , Proffitt et al , Ranglack et al ), which can have social and ecological ramifications. Other elk herds across the West forgo private land as a refuge and continue to rely on traditional forested areas on public land as refuge during the hunting season (Conner et al , Skovlin et al , Wolfe et al , Lamont et al ); however, landscape‐scale alterations to forested areas may well alter the effectiveness of hunting as a tool to regulate such elk populations.…”