Base saturation, nutrient cation, and organic matter increases during early pedogenesis on landslide scars in the Luquillo Experimental Forest, Puerto Rico

Abstract

We evaluate data from a chronosequence study of landslide scars, ranging in age from 1–55+ yr, in the Luquillo Experimental Forest (LEF) a subtropical lower montane wet forest (sensu Holdridge) in eastern Puerto Rico. Surface mineral soil (0–10 cm) base saturation index (BSI) values increase during primary succession in the LEF ( R = 0.85, P < 0.001). Both BSI values and major nutrient cation concentrations are extremely low on new landslide scars. During the course of the 55+ yr chronosequence, major nutrient cation concentrations are positively correlated with soil organic matter (SOM) content ( P = 0.079) and not with clay content ( P = 0.794). When data collected from plots representing the two dominant late-succession vegetation associations are added to the analysis, nutrient cation concentrations correlate significantly with both SOM ( P = 0.001) and clay content ( P = 0.033). Our data show that when initial conditions are oligotrophic, both nutrient cation pools and BSI values can increase in the surface mineral soil during early pedogenesis. We discuss exogenic litter input, substrate weathering, and precipitation as potential sources for nutrient cations in these soils. We further suggest that production and decomposition of SOM is the dominant process controlling capture, retention and intra-ecosystem cycling of nutrient cations in these forests.