Soil properties and hydrologic processes in tropical forest dynamics plots of Panama, Ecuador, and Malaysia

The objective of this research is to systematically characterize soil properties and hydrologic processes of selected tropical forest plots and their associated catchments in Panama, Ecuador, and Malaysia. Few studies have produced a comprehensive, standardized dataset assessing the physical and chemical properties and processes associated with the humid tropics. This is due in part to the natural complexities within tropical forest systems, the inconsistencies in methodologies, and the lack of established sites and related baseline data required to carry out such research. In response, this study implements a standardized rapid assessment methodology at three Center for Tropical Forest Science (CTFS) forest dynamics plots (FDPs) to measure and compare fine-scaled edaphic and hydrologic properties and processes along topographically-defined habitat types (Barro Colorado Island, Panama), topographic gradients (Yasuni National Park in Ecuador), and topographically defined soil properties (Lambir Hills National Park in Sarawak, Malaysia).;Results showed physical and chemical soil properties varying among the plots, with kaolinitic clayey soils high in calcium found in Barro Colorado Island, nutrient-limited silty clay soils derived from quartz in Yasuni, and similarly nutrient-limited sandy to silty clay soils derived from quartz in Lambir Hills. Understanding how these soils respond spatially and temporally to storm events provided a basis for determining the storm-generated mechanisms of overland flow. Measurements of saturated hydraulic conductivity (Ksat) with depth (i.e. soil anisotropy) helped explain the potential flowpaths (lateral, fast flowpaths versus vertical, slow flowpaths) generated from storm events. Rainfall conditions, Ksat measurements, and the presence of overland flow helped assess these sites in light of Elsenbeer's (2001) functional classification continuum of tropical forest soilscapes and hydrologic flowpaths. Hydrochemical signatures indicated movement of water and nutrient export to streams by way of fast flowpaths (deemed the quickflow component) during ordinary storm events, with the contribution of overland flow reaching 17-19% at Barro Colorado Island, 20-37% at Yasuni, and 45-52% at Lambir Hills, during or near peak runoff, as indicated by potassium (K+) and silica (Si).