Observation: The chitemene system of agriculture is widely practiced throughout the wooded lands of northern Zambia. This is a type of slash and burn technique which farmers have learned adds some small value to the soil for cultivating crops. What wood may be harvested is usually converted to charcoal as a demand for it is growing in more urban areas such as Lusaka. Crops typically grown place high demands on the soils themselves, such as with maize, cassava, and sweet potato. When these crops are grown recurrently, they also deplete the soils further. This system of farming has diminishing returns, especially with already weak soils...people tend to farm without any rotations.
As population increases I have observed the areas heavily farmed near population centers are supporting less and less vegetation, in general, let alone diminished yields. Where the soils already seem to be naturally depleted, they are further diminished by farming practices such as recurring use of chemical fertilizers, farming same plots multiple years in a row, and the chitemene system of farming.
Furthermore, in the northern part of Luapula province of Zambia, rainfall is relatively plentiful but, if the trees are cut too low, widespread burning of fields and grasses and forest substrates may lead to mortality of the trees that remain, leading to erosion and additional depletion of soils. In other parts of Zambia, such as in Central and Southern provinces, it appears that widespread practices of chitemene and charcoal production are leading landscapes to desertification. I could do are some pH tests (I have a kit) and look at a sample set of heavily farmed areas vs lightly farmed areas. I'll think about what scientific observation I can make.