The trajectories of mountain socio-ecosystems are complex and influenced by numerous factors (climate, human practices, slope, etc.). This study combined methods used in palynology, ecology and history to produce complementary data to improve understanding of the trajectories of an alpine socio-ecosystem over the last 500 years. Past changes in vegetation cover and land use were reconstructed along with their impacts on erosion dynamics in Montainmont, a commune in the French Alps. A paleoenvironmental analysis (pollen, coprophilous fungi, sedimentology, geochemistry) was conducted on lake sediment, providing a 500-year record of vegetation and erosion dynamics, and mixed farming history. The historical analysis focused on the reconstruction of the customs and habits of the community of Montaimont through the examination of the historical archives of their administrative district. The historical records provided quantitative data on changes in the forest at the plot scale and qualitative information on landscape management. The ecological approach focused on land use analyses using photo-interpretation of aerial ortho-photographs since the 1950s. This data set was used to conduct a spatially explicit analysis of social-environmental interactions in the past. By combining the three approaches, we were able to document changes in vegetation cover over time as well as changes in forestry and agricultural activities. Our analyses reveal a key tipping point during the past century. The community of Montaimont originally used its landscape for mixed farming activities coupled with intensive exploitation of the forest. During the twentieth century, a major socio-ecological change occurred when crop farming ceased, and forest use decreased. This land abandonment led to spontaneous reforestation. This study demonstrates that an interdisciplinary approach bridges the blind spots inherent to each disciplinary approach, facilitating a better understanding of socio-ecological trajectories.