Contrasting effects of wild and domestic ungulates on fine-scale responses of vegetation to climate and herbivory

Context Wild ungulates and livestock modify a large range of vegetation patterns and processes at the landscape scale. However, we still lack studies that address how changes in herbivores' type and management can determine small-scale ecosystem functioning. Objectives We compared landscape vegetation processes within a traditional livestock grazing (transhumant) and a system consisting exclusively of wild ungulates. We also investigated methodological approaches to map very fine spatial-scale changes in vegetation structure and functioning over time in a mountainous Mediterranean system (Iberian Peninsula). Methods We performed different UAV flights per season over exclusion fences, within these two long-term grazing contexts. Later, we processed images to obtain spatially explicit data on vegetation structure (vegetation cover and mean vegetation patch area) and vegetation greenness (NDVI). Results Very high spatial-resolution images provided key information on the spatial distribution and seasonal oscillation of small vegetation patches. Mean annual NDVI showed similar values in both grazing contexts albeit seasonal and annual differences in NDVI between grazed and ungrazed areas. Vegetation cover remained rather constant across seasons but differed between grazing contexts and fencing. The mean vegetation patch area changed seasonally according to the grazing context, without significant differences in mean annual values in fenced and non-fenced areas. Conclusions Accurate image classification helped to uncover differences in vegetation functioning in presence of wild ungulates and livestock. Multi-temporal studies at this fine-scale level improve the detection of ephemeral vegetation patches and increase the comprehension of cascade processes mediated by both ungulate groups, such as vegetation response to climate. The temporal and spatial vegetation patterns should be considered before the implementation of management measures, especially in landscapes within potential rewilding processes.