Pellet Accumulation as a Proxy for Herbivore Pressure in a Mediterranean Ecosystem

Abstract

Human activities have dramatically altered the distribution and density of large herbivores worldwide, particularly on islands. For example, thousands of goats were abandoned to the mountains on Majorca Island, Spain, during the tourism boom in the 1960s. Though this mammal is common throughout the Majorcan mountain range, the impact of goats on the main mountain plant communities has not yet been evaluated. To fill this gap, we recorded goat fecal pellet accumulation and assessed the degree of browsing of 9 363 shrubs and trees located within 231 25-m2 strips systematically distributed in two mountain regions of Majorca. We also recorded the degree of regeneration of woody plants inside the same strips. The environmental factors that significantly influenced pellet accumulation were altitude, rock cover, distance to roads and paths, distance to water, and slope. The correlations between the pellet index and degree of browsing depended on species palatability and abundance. Finally, the natural regeneration of plants was heterogeneously distributed and negatively correlated with pellet accumulation. This study indicates that high levels of browsing of unpalatable species in less preferred areas are a clear indicator of strong herbivore pressure, whereas the presence of nonbrowsed palatable species could indicate low herbivore presence. Moreover, this work demonstrates that the relative abundance of fecal pellets is a good indicator of the pressure exerted by feral goats on vegetation at a fine scale. The simple pellet index used in this work correlates strongly with vegetation damage; thus, it could represent a valuable innovative tool to inform sustainable management of feral goat populations in not only Majorca but probably also other Mediterranean islands. © 2020 The Society for Range Management