The impacts of agricultural expansion on chimpanzees are well recognised, and anthropogenic conversion of natural habitat to other land uses is so extensive in parts of the region that forest-farm mosaics are the predominant modelled habitat type for 5% of western chimpanzees. Conversion of natural habitat for agricultural purposes is so widespread – 1% in only four years – that western chimpanzees are the only African apes for which habitat losses to agriculture could be remotely sensed. Although agriculture did not show a significant effect on chimpanzee densities in a recent model, highest modelled chimpanzee densities are found only in areas with less than 25% cropland cover, suggesting that an upper tolerance limit might exist; however, this varies from country to country.
© Erin Wessling
Subsistence agriculture is small-scale farming by rural communities, employing an estimated 70% of Africa’s workforce. Although West Africa is experiencing increasing rates of urbanization, rural populations are also expected to increase in the coming decades. As human populations grow, local demand for resources accelerates, and this translates into increased demand for arable land. Historically, in Africa, where cropland increased by approximately 25% between 1980 and 2000, agricultural expansion has come overwhelmingly at the cost of intact forests, accounting for 60% of land converted for agriculture, and another 35% at the cost of disturbed forests (Brink & Eva 2008; Gibbs et al. 2010). As such, land conversion for subsistence agriculture directly impacts available habitat for chimpanzees in the region. Shifting farms closer to forest habitats is often another source of negative human-chimpanzee interactions.
Much of West Africa is suitable for agricultural production of coffee, cacao, rubber and palm oil, and such developments are expected to further accelerate chimpanzee losses in the region. Significant habitat losses have already occurred, for example, in Côte d’Ivoire through cocoa production. If investment in an Africa-based oil palm boom continues, some of the last bastions of western chimpanzees – areas suitable for oil palm plantations – could be devastated (Côte d’Ivoire 59.6%, Liberia 81.7%, Sierra Leone 48.8%). Oil palm is native to the region, and chimpanzees incorporate oil-palm and cacao fruits into their diet, some to the extent that they rely on these foods for survival. However, it is likely that most chimpanzees would not survive clearcutting of their habitat, not least because they are unable to exist long term in large-scale monocultures, which lack nutritional and nesting resources, and their presence is otherwise not tolerated.