Slopewash, surface runoff and fine‐litter transport in forest and landslide scars in humid‐tropical steeplands, luquillo experimental forest, Puerto Rico

Abstract

Rainfall, slopewash (the erosion of soil particles), surface runoff and fine-litter transport at humid-tropical steepland sites in the Luquillo Experimental Forest, Puerto Rico (188 20' N, 658 45' W) were measured from 1991 to 1995. Hillslopes underlain by (1) Cretaceous tuffaceous sandstone and siltstone in subtropical rain (tabonuco) forest with vegetation recovering from Hurricane Hugo (1989), and (2) Tertiary quartz diorite in subtropical lower montane wet (colorado and dwarf) forest with undisturbed forest canopy were compared to recent landslide scars. Monthly surface runoff on these very steep hillslopes (248 to 438) was only 0´2 to 0´5 per cent of monthly rainfall. Slopewash was higher in sandy loam soils whose parent material is quartz diorite (averaging 46 g m -2 a -1 ) than in silty clay loam soils derived from tuffaceous sandstone and siltstone where the average was 9 g m -2 a -1. Annual slopewash of 100 to 349 g m -2 on the surfaces of two recent, small landslide scars was measured initially but slopewash decreased to only 3 to 4 g m -2 a -1by the end of the study. The mean annual mass of fine litter (mainly leaves and twigs) transported downslope at the forested sites ranged from 5 to 8 g m -2 and was lower at the tabonuco forest site, where post-Hurricane Hugo recovery is still in progress. Mean annual fine-litter transport was 2´5 g m -2 on the two landslide scars.

A Unified Assessment of Hydrologic and Biogeochemical Responses in Research Watersheds in Eastern Puerto Rico Using Runoff–Concentration Relations

“…The soil surface in the Luquillo forest typically has a shallow litter layer partially penetrated by fine roots. The soil immediately below has abundant fine to coarse roots and an extensive network of macropores created by roots and earthworm burrows (Larsen et al 1999. Soil pipes are visible along cut banks and steep slopes in hillslope and alluvial soils.…”

“…Saturation overland flow occurs along channels and in flow path convergence zones (Schellekens et al 2004). On hillslopes, surface wash appears to be 1-3 % of total rainfall input and is increased by earthworm presence (Larsen et al 1999. Stallard and Murphy (2012) , and PO 4 3-) are recycled and stored in the shallow soil environment by forest biota, and sometimes produced there as well (DOC, NO 3 -, and NH 4 ?…”

Spatial and temporal variability of soil saturated hydraulic conductivity in gradients of disturbance

“…This effect, however, subsides after a short recovery time, as shown by Larsen et al (1999). They reported slopewash rates of recent landslide scars that decreased substantially during a study period of four years to values less than that measured on forested hillslopes.…”

“…In humid tropical environments characterized by steep slopes, high rainfall, and frequent catastrophic events such as hurricanes or earthquakes, landslides are a common phenomenon (Terlien, 1997;Larsen et al, 1999;Vieira and Fernandes, 2004). In montane rainforests of the south Ecuadorian Andes, they are an intrinsic part of the natural disturbance regime.…”

“…The few studies that dealt with the impact of landslide disturbance and recovery on soil properties in pristine ecosystems focused on soil fertility and soil organic matter (e.g., Walker et al, 1996;Singh et al, 2001;Wilcke et al, 2003). Larsen et al (1999) and Hou et al (2005) studied erosion processes and soil fauna, respectively, under undisturbed forest and on recent landslide scars. Regarding soil hydrology, Vieira and Fernandes (2004) investigated the saturated hydraulic conductivity on and next to landslide scars near Rio de Janeiro.…”