Linking forest transition, plant invasion and forest succession theories: socioeconomic drivers and composition of new subtropical andean forests

Context: The patterns and causes of forest transition have been extensively studied, identifying socio-economic drivers of land use deintensification and the associated forest expansion. However, most studies do not take into account the origin of the dominant species of new forests (i.e. native or exotic), which affects biodiversity and the provision of ecosystem services. Objectives: We develop a framework integrating forest transition, forest succession and biological invasion theories to identify the socio-environmental conditions that facilitate different pathways of spontaneous forest transitions in a subtropical mountain basin. Methods: We used Landsat images and Random forest classifier to detect land cover changes over 30 years (1988–2017). We used generalized additive models to identify socioeconomic and biophysical variables associated with expansion of native and exotic-dominated forests. Results: Expanding native forests are scattered throughout the whole basin under a broad spectrum of socioeconomic and environmental conditions. In contrast, the new forests dominated by exotic species were aggregated around their focal introduction areas and their expansion was associated with accessibility and specific land uses (livestock or residential use). Conclusions: Understanding the pathways of alternative forest transition involves the integration of land science, forest succession theory and invasion ecology. Land science explains the availability of sites to be reforested. The species composition of new forests depends on the availability of propagules, dispersal agents and competitive relationships between species (forest succession theory). Invasion ecology explains the role of introduction areas (which are often associated with residential use) of exotic species in the successional process.