Assessing Trail Impacts on Mountain Soil Degradation in the Pyrenees: A Multi-Method Approach

Mountain ecosystems face increasing pressure from outdoor recreation and tourism, with trail-based activities concentrated during snow-free periods when critical biological processes occur. Despite trails occupying minimal surface area, they can contribute disproportionately to catchment-scale degradation. This study investigates soil degradation processes along trails in the Spanish Pyrenees, examining how intensive summer use affects soil properties and contributes to land degradation in these sensitive environments. Using drone-based remote sensing and laser scanning, we quantify actual soil loss along trails, while ground-based measurements assess changes in soil quality parameters.In this context, within the SOLPYR project, we established study sites at three high-use mountain locations (Ibón de Plan, Astún, and Izas) in the Central Pyrenees, characterized by intensive summer outdoor tourism and farmland activities. Our methodology combined drone-based remote sensing, laser scanning, and ground-based measurements to assess trail degradation before and after peak summer use. Soil samples were collected from both trails and adjacent undisturbed grassland to quantify differences in key parameters, including bulk density, moisture content, total carbon, total nitrogen, and soil organic carbon.Preliminary results reveal significant soil degradation on trails compared to adjacent grasslands. Total carbon, total nitrogen, and soil organic carbon concentrations and stocks were substantially higher in grassland soils than on trail surfaces, while bulk density showed the opposite pattern with significantly elevated values on trails. These findings indicate that human and animal trampling causes soil compaction, reduces organic matter content, and potentially accelerates carbon loss from mountain soils.This research highlights trade-offs between recreational land use and soil carbon storage in mountain ecosystems. Given the slow recovery capacity of these environments and their role as carbon reservoirs, our findings will inform management strategies for sustainable mountain tourism while supporting climate change mitigation and soil conservation goals in the Pyrenees.This research project is supported by the SOLPYR project (INTERREG EFA045/01).