Complementary effects of tree species on canopy rainfall partitioning: New insights for ecological restoration in Andean ecosystems

Abstract

Vegetation affects local water balance partitioning via effects on incoming precipitation, local radiation balance and soil hydrological properties. The extent of these effects is related to plant functional traits, such that forest composition plays an important role in its hydrological function. Therefore, the selection of species in forest restoration processes is key to recovering ecological (including hydrological) function. However, most restoration projects often do not include functional criteria for species selection, and even less frequently they include ecohydrological functions, although many projects are intended to recover hydrological regulation. We explored the association between plant functional traits and ecohydrological function, indicated by precipitation partitioning in the canopy into stemflow and throughfall, in an 8-year watershed restoration project in the Central Andes of Colombia. We monitored stemflow and throughfall (both mean and variability) on planted individuals from ten native tree species for almost two years and measured functional traits that describe tree crowns and are associated with rainfall partitioning. We found that stemflow and throughfall behavior is generally inverse and differ among species, with the highest variability in mean stemflow and coefficient of variation of throughfall. Furthermore, our results show that stemflow and throughfall are significantly associated with tree crown functional traits (R2 = 0.74 for crown area and R2 = 0.62 for crown density × volume). Besides, the studied species are organized in a variation space of ecohydrological processes and crown functional traits (first two principal components from PCA explain 71.7% of data variability). They are organized from wider/less dense crowns in Alnus acuminata to smaller/denser crowns in Quercus humboldtii, which significantly influenced the temporal variability of stemflow and throughfall, respectively. Other species are located intermittently along this variation space. From a multivariate perspective, our species were differentiated into four discrete groups based on similar functional traits and, therefore, with similar effects on ecohydrological processes. This suggests a complementary effect of different species on the ecosystem hydrological functions, thus highlighting the importance of considering diversity on ecosystem management and ecological restoration for the recovery of ecosystem integrity.