The Role of Land Use Intensity on Vegetation Recovery Gradients After Land Abandonment in the Semiarid SE Alentejo, Portugal

Abstract. Understanding how land use history shapes secondary succession is crucial for semiarid regions, where human pressures intersect with climatic variability. This study examines the Serra de Serpa e Mértola, in SE Alentejo, Portugal, an area marked by extensive land conversion and degradation over the 20th century. Drawing on long-term monitoring of experimental plots at the Vale Formoso Soil Erosion Centre, we leverage UAV-based photogrammetry to quantify vegetation recovery dynamics from 2018 to 2024. By focusing on canopy height models (CHM), we move beyond traditional spectral indices to directly assess biomass accumulation over time. Preliminary findings reveal clear differences in recovery trajectories linked to historical land use intensity and climate conditions. Plots with lower historical disturbance, such as light grazing or spontaneous vegetation, exhibit faster recovery, while intensively managed plots show slower biomass gains and signs of ecological thresholds. Our results highlight the value of UAV monitoring for understanding how abandonment starting points influence ecosystem resilience under varying climatic pressures, offering insights for restoration strategies in Mediterranean semiarid landscapes.