Constituents and drivers of composition, diversity and structure of a Congolese forest

Abstract

Tropical forest systems occupy 2% of the earth’s land surface but host nearly 50% of the world’s forests and support unique flora and fauna and ecological processes. They also provide a multitude of ecosystem services ranging from the provision of food and water to supporting livelihoods and climate change mitigation. However, tropical forests are under immense anthropogenic pressures, including conversion of forestland for agricultural purposes, logging and extraction of timber, and exploitation via hunting and poaching. These pressures fragment forests and alter ecological processes that are linked to the many ecosystem services they provide. The Congolese forest of Central Africa is an important tropical forest belt of the world with a unique history of anthropogenic pressures, particularly logging and hunting activities. In this study, I examine the forests of the northern Republic of the Congo to understand the role of logging and hunting on forest diversity, composition, and structure. Specifically, I identify forest tree communities and determine the extent to which environmental drivers versus anthropogenic disturbance dictate forest composition, diversity and structure. To do so, I use a range of statistical techniques, including non-metric multidimensional scaling, classification and multi-level pattern analysis and multiple regression approaches. The results of my study reveal that variation in species composition is explained by disturbance type (combination of logging and hunting, logging only, and no disturbance), distance to Kabo village (proxy for disturbance), and logging. I determined five tree species groups across the study area that largely represents a gradient of disturbance. Areas having combined pressures of hunting and selective logging included the highest number of species groups, while pristine areas included the lowest number of species groups. In addition, the indicator tree species characterizing the species groups also reflected the level of disturbance, with highly disturbed plots containing more characteristic secondary tree species and pristine areas containing primary tree species. For drivers of tree species diversity, I concluded that edaphic factors including pH and phosphorous explain variation in diversity. Lastly, I determined there to be no significant driver of basal area across the plots, but variation in wood density was driven by total nitrogen and soil texture. My study highlights the effects of disturbance on species composition across this forested landscape; whereas soil characteristics seemed to have a stronger role in controlling forest diversity and structure, although additional research is needed to fully elucidate the observed results. More studies are needed to decouple the effects of anthropogenic pressures and environmental factors on forest composition, diversity and structure, thereby providing more insight about these forests.