African forest collapse, recovery and chimpanzees?

Most people think of the mythical tropical forests of Central and West Africa as having been there from the dawn of time, even if global climate fluctuations such as the waxing and waning of glaciers may have influenced them to some extent. On the other hand, and on a much more recent scale, one might also think humans have directly impacted them for millennia, but it appears this is not the case.

A major study just published in the journal Global Planetary Change by researchers at the Universities of Perpignan, Montpellier and Sussex, which combines numerous pollen records to reconstruct the vegetation, shows that 2500 years ago, a large part of the rainforest canopy was broken up, and the forests became fragmented, allowing a much more open vegetation, such as savannas, to colonize.

“However, the massive geographic scale of this forest collapse at the same time was nothing to do with human impact as there were too few people in this area as revealed by the very limited archaeological record”, says Pierre Giresse, the lead author, “and in fact for approximately 500 years, it was due to the length of the dry season increasing. Indeed, the forests as we know them in their present form began only from 2000 years ago.”

“Nevertheless, most of the rainforest expanded again over the following centuries, aided by the early colonization of light-demanding species, such as the oil palm”, notes Jean Maley. “This species may be causing destruction due to its commercial importance in other tropical areas of the world today, but its origin is in Africa, where due to its nutritional and calorific content it helped the migration of Bantu people through the forest to eventually reach East and Southern Africa. But they were not planting it or destroying the forests, as it grew up spontaneously and its fruits were easily collected”

“It is less appreciated that a major factor in the resilience of the rainforests to bounce back were due to natural processes, particularly the many animals, such as chimpanzees, which dispersed fruits, for example, the oil palm in their nutrient-rich poo”, says Alex Chepstow-Lusty. Curiously much of the regeneration occurred against the backdrop of increasing human populations.”

“But compared to 2500 years ago, the situation is now very different, with both climate change and human pressures being experienced.”

“Sadly”, says Jane Goodall, the well-known conservationist, who was not involved in this study, “the demand for bushmeat, including many of the vital fruit dispersers like chimpanzees, is not only likely to make forest regeneration less possible, but facilitating the transmission of diseases to humans. We have many reasons to conserve our closest relatives, but they are also helping us conserve the rainforests and maybe even shaping it for their own nutritional needs.”