Prioritizing West African medicinal plants for conservation and sustainable extraction studies based on market surveys and species distribution models

Abstract

Sub-Saharan African human populations rely heavily on wild-harvested medicinal plants for their health. The trade in herbal medicine provides an income for many West African people, but little is known about the effects of commercial extraction on wild plant populations. Detailed distribution maps are lacking for even the most commonly traded species. Here we combine quantitative market surveys in Ghana and Benin with species distribution models (SDMs) to assess potential species’ vulnerability to overharvesting and to prioritize areas for sustainable extraction studies. We provide the first detailed distribution maps for 12 commercially extracted medicinal plants in West Africa. We suggest an IUCN threat status for four forest species that were not previously assessed (Sphenocentrum jollyanum, Okoubaka aubrevillei, Entada gigas and Piper guineense), which have narrow distributions in West Africa and are extensively commercialized. As SDMs estimate the extent of suitable abiotic habitat conditions rather than population size per se, their output is of limited use to assess vulnerability for overharvesting of widely distributed species. Examples of such species are Khaya senegalensis and Securidaca longipedunculata, two trees that were reported by market vendors as becoming increasingly scarce in the wild. Field surveys should start in predicted suitable habitats closest to urban areas and main roads, as commercial extraction likely occurs at the shortest cost distance to the markets. Our study provides an example of applying SDMs to conservation assessments aiming to safeguard provisioning ecosystems.