Abstract:
Bimodality in the distribution of tropical tree cover at intermediate environmental
conditions is cited as evidence for the presence of bistability in the
forest-savanna system. However, bimodality can also emerge because
of human activities that cause changes in tree cover, such as the deforestation
resulting from expansion in settlements, agricultural and pasture
lands. Also, the impact of such activities on tree cover can persist beyond
the site of disturbance. Here, I study the relation between human influence
and tree-cover bimodality in sub-Saharan Africa, in order to draw conclusions
regarding the vegetation dynamics prevalent in the region. I divide
remote-sensed vegetation data into regions with low and high degree of
human influence. In addition, I devise an environmental predictor of tree
cover using relevant climatic and edaphic variables. It is hypothesized that
a higher extent of bimodality will be observed in regions with high human
influence, because of bimodality arising from human activities, as opposed
to bistability. The results show that bimodality is found in regions with both
high and low human impacts. However, the extent of bimodality is lower
in the regions with low human influence. This indicates that while bistability
is restricted to smaller spatial extents than previously assumed, it is
common across sub-Saharan Africa, regardless of the presence of human
influence.
