EFFECTS OF SELECTIVE LOGGING ON CARBON DYNAMICS: VARIATION IN ABOVEGROUND BIOMASS AND SOIL RESPIRATION IN PRE- AND POST-LOGGING FOREST STANDS OF A MOIST TROPICAL FOREST IN GHANA

Abstract

Tropical forests play an important role in the global carbon cycle, but are threatened by human activities, particularly selective logging, which is projected to increase in extent and intensity due to the demands of a rapidly growing human population. Yet, the impacts of selective harvest on carbon dynamics of residual forests is poorly understood. This dissertation examines the effects of selective harvest involving twice the standard logging intensity in Ghana (6.5 vs. 2 to 3 trees ha-1) on aboveground biomass (AGB) and soil respiration in pre- and post-logging forest stands of a moist semi-deciduous forest in Ghana. Using standardized protocols, data were collected in one-hectare plots to observe variation in AGB and soil respiration before and after selective harvest. Prior to logging, AGB was 318.6 Mg ha-1. However, one year after the removal of 121.6 m3 ha-1 of timber trees, AGB declined by 16.9%. Variation in AGB both before and after logging was better explained by species dominance and functional diversity than by species richness. In particular, the dominance of certain species influenced carbon storage before and after logging, due, in part, to environmental filtering of species based on plant functional types and/or life form. While C storage in trees was associated with LAI before logging, LAI was most important for liana C storage after logging. There were significant differences (P ≤ 0.05) in seasonal variation of soil respiration before and after logging, and between a 10- and 20-year post-logging stands with soil respiration higher in the wet season. Similarly, there were significant differences (P ≤ 0.05) in seasonal variation among components of soil respiration in the 10- and 20-year post-logging stands. Autotrophic soil respiration was 33% higher in the 20-year post-logging stand while heterotrophic soil respiration remained similar between the two stands. In general, soil moisture was the most important factor influencing soil respiration across the post-logging stands and for components of soil respiration, particularly root and mycorrhizal respiration. This information about patterns and underlying controls on soil respiration from different soil components should aid attempts to accurately model soil respiration over space and time