Article III. The functional and structural characteristics of forest canopies drive distinctive throughfall patterns between old-growth and second-growth neotropical rain forests
Chain Guadarrama, Adina
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1. Relationships among forest plant diversity, canopy structure, and forest hydrology have long been recognized. However, there is a great need to study how metrics of forest biodiversity may be linked to hydrologically-based ecosystem service provisioning. 2. In this study we quantified the relationship between two key components of this link: the functional and structural characteristics of tropical moist forest canopies and rainfall redistribution. 3. We measured forest structural and functional characteristics and throughfall under oldgrowth and second-growth forest canopies (n=14) of northern Costa Rica to understand how key vegetation properties correlate with the mean and variance of throughfall over time and space. 4. Throughfall was directly affected by rainfall amount (ANCOVA, F = 1164.1, p < 0.0001). While mean throughfall did not differ between old-growth and second-growth forests, we observed an effect of forest type on the spatial variation of throughfall (ANCOVA, F = 16, p = 0.0001). Higher throughfall heterogeneity was observed in old-growth forests under low rainfall in comparison to second-growth forests, whereas the latter showed no change in throughfall heterogeneity with changes in rainfall magnitude. Spatial differences were related mainly to the differential abundance of palms, with greater number of these individuals in old-growth forests. In particular, palm occurrence was found to be a fundamental driver of relationships found between structural metrics (i.e. canopy cover), functional metrics (i.e. specific leaf area weighed mean), and throughfall (R2 adj = 0.15, deviance explained 18%). 81 5. These findings confirm the role of palms as an a priori functional group in Neotropical forests and support the stated relationship between biodiversity and forest hydrological processes. Our results also indicate what traits may be most valuable for the purpose of understanding the relationship between tropical forest functional diversity and partitioning of rainfall, and how the functional approach may complement measures of forest structure and canopy cover for this purpose. In addition, this work highlights the need to understand how potential changes in the hydrological cycle in these ecosystems may occur with future shifts in species and functional group composition, as occurs due to forest succession.