Conservation and management of the terrestrial carbon held especially in forest ecosystems is crucial to meeting climate change mitigation objectives. It is important to improve our knowledge of both the anthropogenic and natural controls that affect the distribution and dynamics of terrestrial carbon. Focusing on the dry tropical forests of Zambia, in the Southern Africa region, this study provides the first large-scale assessment of human and natural controls over aboveground tree density for the region, by making use of the first Zambian nation-wide forest inventory, covering both human-dominated landscapes and remote areas. Multiple regression models with variation partitioning and Boosted Regression tree models were compared in order to identify predictors that best explain the variation in biomass density, contrasting anthropogenic and natural sites at different scales. Species ranking and correlation tests were used to compare those sites on different stand structure characteristics and species composition, as well as analysis of variance to evaluate the impact of different management and conservation practices on biomass density.
Results/Conclusions
By comparing human and natural forest sites in Zambia across spatial scales, this study brings key insights into the factors controlling variability in AGB density in Africa tropical dry forest ecosystems. One of our key findings is that variation in tree biomass density is mostly explained by biotic processes, linked with both species richness and dominance (evenness), which explained more of the variation than environment, spatial structure or even land use variables. In the case of natural forest sites, diversity is one of the key factors explaining this variation in conjunction with environmental controls. For human-dominated sites, the variation is explained jointly by diversity and land use. Biomass density was negatively associated to tree species evenness and positively associated with species richness. Stand structure characteristics including stand-level mean and dominant tree species characteristics were the best correlates to biomass density. The influence of human activities on biomass density in managed sites appears to be mediated by impacts on species diversity and dominance, as well as on stand structure characteristics. This research also provides the first evidence of positive outcomes of protected areas and participatory forest management policy approaches to protect and manage forest carbon stocks in Zambia.