Forest ecosystem services at landscape level - Why forest transition matters?

Forests in the humid tropics contribute to a wide range of globally demanded forest ecosystem services (FES) and are also beneficial to local communities, which are often highly dependent on natural resources. Approximately one-third of these forests are threatened by resource extraction, logging, and the expanding agricultural frontier. As a result of these developments, forest landscapes are shaped by a transition gradient representing areas with a high forest cover to locations resembling agricultural-forest mosaics. These transition gradients are often characterized by different types of forests and successional stages. We used inventory data from 331 plots collected in 24 landscapes in Ecuador and the Philippines, representing five forest-based land-use types. We used mixed linear effect models to analyze how the landscape transition gradient and forest type affect various forest ecosystem services. Additionally, we identified stand structure and landscape transition gradients that influence changes in these FES. Results show country and forest type specific reactions for different FES. For example, aboveground carbon, non-timber forest products, biodiversity, and timber volume in natural forests are not only affected by logging but also decline along the landscape transition gradient. This includes the risk of extinction of high conservation species and long-term depletion of timber resources. We show that tree-based secondary land-use systems may partially compensate for the loss of some FES, especially timber supply, but found evidence for increased nutrient depletion in agroforestry systems. Our results highlight the importance of connected forest landscapes and structurally diverse forest stands in early transition landscapes. We suggest conservation and restoration strategies sensitive to the transition context for FES and to make better use of the various benefits of tropical forests in a sustainable manner.