Dynamic patterns in winter ungulate browse succession in the Boreal Plains of Alberta

Abstract

Wildfires are a key driver of boreal forest structure and community composition that alter food resources affecting the behaviour and ecology of wildlife. In the first 50 years post-wildfire, woody browse availability in upland forests increase in quantity and quality for generalist ungulates, such as moose (Alces alces) and white-tailed deer (Odocoileus virginianus). Greater favorable habitat for these generalist ungulates results in increases to their respective populations, and through apparent competition, leads to increases in wolf populations; thus, causing unsustainable levels of predation on threatened woodland caribou (Rangifer tarandus caribou) populations. However, the duration of post-wildfire browse availability is not well understood in the Boreal Plains of Alberta as previous studies are primarily from the Taiga and Boreal Shield where vegetation communities are structurally different. This study examines the changes in winter browse richness, evenness, abundance, and community composition, as well as their use (browse levels) by moose and white-tailed deer, over a 150-year post-wildfire period. In the summer of 2019, we collected vegetation and ungulate browsing data from 164 upland and lowland forest sites in northeastern Alberta, Canada. We used analysis of covariance (ANCOVA) and ordinal logistic regression to examine changes in browse measures. Species richness and evenness showed a double peak at 10–25 years and 90 years post-wildfire in mixedwood forests, as a result of fluctuations in browse palatability, while browse abundance was constant. In contrast, black spruce and lowland forests had similar species richness, evenness and abundance over the 150-year chronosequence. However, browse abundance in lowland forests was higher than mixedwood forests, but this consisted of low palatable browse. Browsing was significant in jack pine forests, mixedwood forests and poor fens; coniferous saplings were generally avoided, whereas 35–65% of available deciduous saplings were browsed. Understanding post-wildfire succession and ungulate browsing in post-wildfire forests provides useful information for managing alternative prey populations necessary for long-term woodland caribou conservation.