Litter Dynamics and its spatial heterogeneity on the hillslope
According to the study by Miranda and Avelar (2019) conducted at the same hillslope positions, there are small spatial variations in vegetation structure linked to the topographic gradient. The main variant elements are the lower density of tree individuals in the downhill direction and the higher presence of dead trees and palm trees at the SMT, as well as lower and more open canopy vegetation at this hillslope position. In short, the SMT exhibits a less wet and more slightly lighted forested environment compared to the other positions (figure 2).
The spatial variation observed in the vegetation structure does not materialize in a significant difference in the annual litterfall between the different hillslope positions. At the time of litter-fall, debris can be spatially redistributed by downhill movement on steeper areas without the need for water-carrying action. Additionally, leaves (or leaf fragments) and seeds already deposited above ground can be moved downhill through the possible influence of overland flows. However, the occurrence of surface runoffs is sporadic in the area and the redistribution of debris by water is non-massive. The infiltration capacity is enough for the occurrence of hortonian flows to be uncommon. Saturation-excess overland flows caused by heavy rainfall may occur confined to small ephemeral drainage channels.
The litter moisture increases in the downhill direction and controls the efficiency of decomposition on the hillslope, with the differentiated decomposition rates being the main driver for the heterogeneity of litter accumulation above ground. The SMT area stands out with its thick litter stock as a result of a less favorable environment for decomposition, considering that the lower moisture content is combined with the higher presence of palm trees (more recalcitrant leaves), where a large accumulation of semi-composed material is observed. In contrast, the VBT exhibits a thin litter stock as a reflex of the most efficient decomposing action, where there is very little accumulation of semi-composed material. The two mid-hillslope positions (HHS and LHS) have similar litter stocks, with intermediate accumulation between that observed in SMT and VBT, while SMT has a 3x higher stocked mass than VBT. Lastly, SMT exhibits topsoil (20 cm) richer in OM, while VBT has the lowest content, given the OM mineralization efficiency.