Ungulates Attenuate the Response of Mediterranean Mountain Vegetation to Climate Oscillations

Abstract

In regions with a long-standing history of grazing pressure, vegetation has co-evolved with herbivores by developing intrinsic functional dynamics. Although this type of trophic interaction has been recognised as being important for shaping how vegetation responds to climate, better knowledge about how this process occurs on the landscape scale and over a long time range is necessary. Here, we evaluated the potential roles of herbivores in modulating the response of mountainous Mediterranean vegetation to seasonal and longterm climate oscillations. To understand the relations among climate, plants and animal population, we fitted a Bayesian model to a combination of long-term (1995–2014) climate datasets, satellite greenness maps (NASA Landsat NDVI) and exotic Barbary sheep census data (breeding success and abundance of Ammotragus lervia). We also used the intrinsic mode function and Hilbert spectrum transformations to decompose NDVI time series and to evaluate their periodic oscillations. We found remarkable dissimilarities as to how climate affects the temporal oscillation of vegetation greenness between landscapes both with and without ungulates, albeit their similarities under environmental conditions. Vegetation responses to climate are particularly attenuated in landscapes with ungulates, an effect that depends on ungulate population abundance. In a world where extreme climate events are becoming frequent and intense, our results indicate that ungulates can strongly modulate how grasslands and scrublands respond to climate change. Increasing our knowledge as to how this type of trophic interaction affects vegetation responses to climate variability is of much importance for managing ungulate rewilding strategies.