Ecological Indicators (Jun 2024)
Browsing intensity as an index of ungulate density across multiple spatial scales
Abstract
Large herbivores can profoundly influence terrestrial ecosystems. Through browsing, for example, they can impact forest regeneration with consequences for both plant and animal species. Understanding the drivers of ungulate browsing is therefore crucial from a conservation and management standpoint. Browsing is generally thought to be affected by ungulate density, such that increased density leads to greater browsing probability. As a result, browsing has been suggested as an indicator of ungulate density. While most studies investigated long-term browsing impact of ungulates in single study areas, few of them focused on different spatial scales using multiple replications in time and space. In this study we took advantage of 25 years of browsing data within the Stelvio National Park (central Italian Alps) derived from several populations of red deer and modelled the ratio of browsing on conifers (calculated as browsed conifers divided by total number of conifers) as a function of two different density indices at different spatial scales and a set of environmental covariates. Specifically, we investigated whether variations in red deer density at different spatial scales reflect variations in browsing probability. The results suggest that as deer density increased, the ratio of browsing increased at all spatial scales, at times mediated by shrub species diversity. Density was a consistent driver of browsing probability within all deer populations, while the effect of confounding variables was statistically unclear as they yielded conflicting results for the different populations, failing to find common patterns. This study highlights that density at different spatial scale is an important predictor of browsing probability, suggesting that browsing could be a reliable indicator of variations in ungulate density. In turn, as browsing can map small- and large-scale density variations, pattern of browsing impact may be a useful tool to investigate small- and large-scale changes in red deer densities due to disturbance factors such as human activities or the presence of large predators.
