Impacts of black bear baiting on Acadian forest dynamics – An indirect edge effect?

Abstract

Many biotic factors impact forest health and productivity and an important damage agent in many forests in North America is the black bear ( Ursus americanus). Black bears use trees for feeding and marking purposes, both resulting in cambial damage, which reduces growth rates and can increase mortality rates. Black bear behavior is strongly impacted by human activities including forest management and supplemental feeding. During the 2010 permanent sample plot census and tree health survey in Fundy National Park, New Brunswick, Canada we measured high rates of bear damage; roughly 10% of the sampled population experienced damage in a non-uniform way within the Park. The goal of the present research was to examine the spatial distribution of bear damage, determine underlying causes of spatially non-homogeoneous bear damage and quantify the impact of this damage on forest dynamics. Bear damage was more frequent around the periphery of the Park and using spatial scan statistics, we identified two clusters of bear damage, both at the Park’s inland borders and adjacent to areas of high bear hunting baiting station density. Species differed in the extent of damage, with hardwood species incurring proportionally greater damage. Using multiple regression we modeled bear damage as a function of stand type (%hardwood), stem density, proximity to and density of bait stations and distance to the nearest major edge. Models containing stand type and bait station metrics garnered the greatest support based on minimum AIC analysis. Bear damage was greater in hardwood stands and in sites closer to or in areas of higher density of bait stations. Bear damage had a significant negative impact on forest dynamics; 2005–2010 diameter growth showed significant reductions in response to bear damage. Our findings implicate bear bait stations used by hunters in aggregating black bears at the Park periphery where they cause greater damage to the trees, which results in reduced growth rates in these areas. Effectively, high bait station densities surrounding the Park are contributing to two related edge effects: (1) increased activity in and use of forests at the Park edges by bears; and (2) increased damage and decreased growth in peripheral stands where bear activity is high. Continued heavy bear damage could pose a threat to forest integrity along the boundaries of the Park. Thus, despite the high protection afforded this National Park, its function and long-term integrity is impacted by adjacent land uses as demonstrated by the present study, an increasingly widespread problem facing protected areas.