Water and nutrient cycling regulation functions in forest ecosystems: a comparison between native forests and exotic fast-growing tree species plantations in tropical highlands

An improved understanding of ecosystem functions is increasingly needed as ecosystem management moves towards optimizing their capacity to provide services to society. Such a task requires the characterization of ecosystem functions in strategic systems such as tropical mountain forests, which are also subject to pressure due to both global and local environmental changes. In particular, transformation of native forests into pastures or agriculture, has been regarded as the type of transformation with the largest effects in ecosystem regulating and provision functions. However, the effects of other transformations such as those associated with replacement of native with planted forests, have been less studied. To evaluate the effect of forest type on key-ecosystem functions related to water resources, we studied the dynamics of rainfall partitioning and nutrient circulation on a suite of representative forest types in neotropical mountain systems: two plantations of exotic fast-growing species and two types of native forests. Our results illustrate that, when considered in a per-basal unit area, water transmission to the forest floor is significantly higher in both native forests. Similarly, native forests are more effective on circulating nutrients on the ecosystem as they are better adapted to oligotrophic soils such as those occurring in tropical mountains. These results suggest that the replacement of native forests with exotic tree plantations can potentially impact hydrological regulation and the nutrient cycling in these high Andean lands, affecting both directly and indirectly the capacity of ecosystems to produce services to society.