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Africa’s carbon (C) cycle is one of the least well understood components of the global C cycle. Miombo woodlands are the most common woodland type in southern Africa, but despite their vast extent and importance in the biogeochemical cycles of Africa, their C dynamics are not well understood. This thesis addresses a set of science questions related to miombo woodland C dynamics that cover a range of scales, from the leaf to the landscape. The questions are related to seasonal controls on C uptake at the leaf level, to spatial distributions and scales of variation of C stocks in the landscape, and to the drivers and spatial patterns of deforestation and degradation at the regional scale. In miombo woodlands, the seasonality of productivity remains poorly understood, and it is unclear whether stomatal limitations or variations in leaf traits cause seasonal changes in productivity. I use data of leaf gas exchange and leaf traits collected in dry and wet seasons to assess the response of photosynthesis to seasonality. I found a large degree of inter-specific responses, where photosynthetic capacity was maintained between seasons in some tree species but not in others. This was linked to inter-specific stomatal regulation on leaf gas exchange, access to soil water and varied leaf traits, indicating differing timing of leaf development during the dry season. Differing timing of leaf flushing can create niche separation, facilitating the co-existence of miombo woodland tree species. I use data collected along a 5 km transect through miombo woodland to characterise the spatial distributions and scales of variation of C stocks in woody biomass and soils, and assess the links between them. I found that on the scale of a few meters, soil C stocks varied in relation to soil texture. At the kilometre scale, surface soil and woody C stocks were coupled, and varied in relation to topography. By understanding the scales of variation I was able to make recommendations for optimal sampling of C stocks in a miombo woodland landscape for improved C stock assessments. I developed and tested a simple spatial model of deforestation and degradation, using a rule-based approach, to produce risk maps of areas more likely to be affected by deforestation and degradation for a study site in central Mozambique. I found that my model was able to accurately predict the locality of high risk areas, and that roads were the major axis for forest biomass loss. Risk maps created from this method are useful for exploring the drivers of deforestation and degradation in a region dominated by miombo woodland, and for targeting policy and management efforts. Overall, this thesis has contributed significantly to our understanding of natural and human driven miombo woodland C dynamics over a range of scales, from the leaf to the landscape. In the final chapter, I discuss the implications of each chapter for our understanding of miombo woodland C dynamics, and suggest areas for further research.

The savanna woodlands of Southern Africa, colloquially termed the miombo, are poorly described in terms of biodiversity compared to other biomes. They have therefore been underrepresented in the wider understanding of how land use intensification is shaping global biodiversity. Land use change is known to reduce biodiversity and disrupt intactness of ecological communities with consequences for ecosystem functioning, resilience, and services. Miombo woodlands are described as biodiversity hotspots due to a high endemism of species and the presence of megafauna. At the same time, they are also considered dynamic socio-ecological systems shaped by disturbances and the land use activities of people. The patterns of biodiversity change in these tropical ecosystems may, therefore, have their own unique contexts, understanding of which will be essential for biodiversity and land use management in these ecosystems. In this thesis, I identified the patterns of biodiversity change in response to the two major land use practices in the two dominant woodland types in southern African woodlands: the selective logging due to charcoal production in the mopane woodlands, and agricultural expansion in the miombo. I also examined the impact of two main disturbance agents, humans and elephants, on habitat structure and biodiversity in mopane woodlands. Across all chapters in this thesis, I investigated the effects of land use change and habitat modification on biodiversity empirically using chronosequences. To understand biodiversity change, I employed a hierarchical multilevel modelling approach making inferences at the three levels of ecological communities: species, community, and meta-community (set of ecological communities at different sites). I selected six villages in the charcoal production hotspot of southern Mozambique and carried out field surveys for three taxonomic groups: trees, mammals and ground beetles. I modelled the counts of trees and beetles and incidence of mammals using meta-community occurrence models in a Bayesian framework with the intensity class of the villages, above-ground biomass and land cover type as predictors. The results suggested that the species richness of trees and mammals declined by 12 and 8.5 % respectively while that of beetles increased by 3.5%, albeit non-significantly. In addition, the beta diversity of trees decreased while that of mammals increased. The results show that while both trees and mammals reduced in richness, they responded differently to charcoal production in terms of community organisation. The trees underwent subtractive homogenisation (decrease in alpha and beta diversities) primarily because of deterministic processes induced by selective harvesting of tree stems for charcoal. Mammal communities, on the other hand, showed subtractive heterogenization (decrease in alpha, but increase in beta diversity) mainly due to random extinctions. In the agriculture frontier of miombo-dominated northern Mozambique, I investigated the effects of fragmentation and habitat loss caused by agricultural expansion on diversity and composition of trees and mammals. I modelled the occurrences of trees and mammals using occupancy models with the fragmentation and quantity of woodland cover as predictors. The model showed that most tree species (n=10), mainly the timber and firewood species, linearly declined in population size as fragmentation increased. Mammals, on the other hand, showed a nonlinear response. Seven mammal species increased at the lower levels of fragmentation. However, at the higher levels, none of the mammal species increased while two declined. Similarly, the species richness of trees linearly declined, while that of mammals increased up to a fragmentation level of 55-65% and declined above this limit. The beta diversity of trees increased with fragmentation while that of mammals decreased. The results suggest that, although fragmentation reduces species richness of both trees and mammals, it affects their species compositions in different ways. Trees undergo subtractive heterogenization due to random species losses while mammals experience subtractive homogenisation mainly due to the combined effects of fragmentation-led habitat loss and intensified hunting. Finally, this study concludes that, above 75% fragmentation or below 26% habitat quantity, both taxonomic groups endure biodiversity loss. The threshold results here corroborate similar habitat quantity thresholds (20-30%) observed elsewhere in different ecosystems. However, they differ with the widespread notion that above 30% habitat quantity, the effect of fragmentation is non-existent. The results here emphasize that taxonomic groups respond differently, the diversity and population size of mammals reduced only after the habitat threshold, whereas, those of trees showed linear decrease with fragmentation most likely due to fragmentation-led habitat loss. Lastly, I examined the effects of disturbance by humans and elephants on habitat structure and bird diversity by conducting a space for time substitution comparison in the mopane woodlands of Zambia. To examine the woodland structure, I modelled the structural attributes of habitat (stem diameter, stand density, and basal area) using mixed models with the proportion of affected stems by humans and elephants as explanatory variables. I found that elephant disturbance was associated with higher stem diameters, low stand densities, but no change in basal area. Human disturbance, on the other hand, was related to reductions in stand density and basal area, but no change in the stem diameter. Further, I tested species and functional diversity of birds against the covariates of habitat structure and disturbance. I found that bird communities reduced in species richness in both, human as well as elephant disturbed areas. However, the functional diversity did not change with elephant disturbance. I concluded that human disturbance reduces woody biomass (basal area is correlated with woody biomass) of mopane woodlands and functional diversity of birds whilst elephants do not. In this thesis, I conclude that human driven land use change in the miombo woodlands erodes alpha diversity of all taxonomic groups. However, increases in beta diversity of mammals with charcoal land use and trees in agricultural land use may maintain their diversities at the meta-community level.