30An improved understanding of ecosystem functions is increasingly needed as ecosystem management moves towards 31 optimizing their capacity to provide services to society. Such a task requires the characterization of ecosystem functions in 32 strategic systems such as tropical mountain forests, which are also subject to pressure due to both global and local 33 environmental changes. In particular, transformation of native forests into pastures or agriculture, has been regarded as the 34 type of transformation with the largest effects in ecosystem regulating and provision functions. However, the effects of other 35 transformations such as those associated with replacement of native with planted forests, have been less studied. To evaluate 36 the effect of forest type on key-ecosystem functions related to water resources, we studied the dynamics of rainfall 37 partitioning and nutrient circulation on a suite of representative forest types in neotropical mountain systems: two plantations 38 of exotic fast-growing species and two types of native forests. Our results illustrate that, when considered in a per-basal unit 39 area, water transmission to the forest floor is significantly higher in both native forests. Similarly, native forests are more 40 effective on circulating nutrients on the ecosystem as they are better adapted to oligotrophic soils such as those occurring in 41 tropical mountains. These results suggest that the replacement of native forests with exotic tree plantations can potentially 42 impact hydrological regulation and the nutrient cycling in these high Andean lands, affecting both directly and indirectly the 43 capacity of ecosystems to produce services to society. 44 45

Understanding ecohydrological dynamics that result from land-use conversions is fundamental in managing ecosystem services. One common forest transformation in the tropics is the establishment of monospecific plantations with exotic species for timber exploitation, replacing highly diverse natural forests. The impacts of establishing forest plantations in hydrological processes and biogeochemical dynamics, have been highly controversial, with functions from structurally homogeneous plantations being sometimes assumed to be comparable to natural forests. To assess the effects of planting exotic conifer species versus natural forests on hydrological and biogeochemical functions, we measured incoming precipitation, throughfall and stemflow. To compare between forest types, we propose the use of basal area for standardization of hydrochemical fluxes. While net precipitation was similar among forest types, the transmission of water to the forest floor per basal area unit was significantly higher in native forests. Yet, nutrient concentrations were similar among them. However, greater nutrient enrichment per unit basal area was observed for the native species. This more efficient nutrient cycling could be related to native forests being better adapted to oligotrophic soils. The re-establishment of native species rather than with exotic species can result in more efficient hydrochemical regulation, improving the capacity of these ecosystems to produce services.