A regime shift in soil moisture triggered by selective logging in Bornean lowland tropical rainforests

Abstract

Context Aboveground biomass removal and canopy opening by selective logging modifies soil moisture in the main root zone, impacting soil aeration and various biogeochemical processes in tropical production forests. Objectives This study investigated the relationship between canopy damages and topsoil (10 cm) moisture in logged-over forests in Malaysian Borneo, controlling for logging intensity, time elapsed from logging, and spatial autocorrelation. Methods Volumetric soil water content (VSWC), canopy height model (CHM), leaf area index (LAI), and historical logging data were collected from 84 transects in 15 sites exhibiting varying canopies. Principal component analysis (PCA) was applied to canopy structure metrics (CSM) derived from CHM and LAI for each transect. The first principal component (PC1) quantified canopy structural degradation and was analyzed in comparison to topography for the relationship with VSWC across logging periods. VSWC spatial autocorrelation was examined in relation to canopy conditions. Results VSWC increased from 0.27 m³ m^− 3 to over 0.4 m³ m^− 3 after logging. In the study area, PC1 was a stronger predictor of VSWC than topography was. Wettest soils were found underneath the most degraded canopies, despite of a higher evaporative demand combined with higher vapor pressure deficit. Conclusions This study revealed soil wetting after selective logging in humid tropical forests, driven by reduced transpiration from biomass loss rather than increased evaporative demand from canopy opening. The elevated soil water regime could disrupt carbon and nitrogen cycling and impede forest succession, and its coupling with increased evaporative demand increases the overall vulnerability of disturbed tropical rainforests.