Road mediated spatio-temporal tree decline in traditional agroforests in an African biosphere reserve

Understanding the role of protected areas in conserving biodiversity is a central goal in conservation biology. Anthropogenic activities around and inside these protected areas and, in particular, roads can alter the spatiotemporal dynamics of biological diversity in protected areas. However, our understanding of how the presence and position of roads affect human attitude, subsequent agricultural practices and biodiversity conservation is limited. In this study, we tested the effects of the proximity of traditional agroforestry parklands to main roads used by park rangers for surveillance on the diversity and abundance of woody species in the Pendjari Biosphere reserve over 16 years (2000–2016). Tree density in agroforestry parklands decreased over time from an average of 20 trees/ha in 2000 to 7 trees/ha in 2016. Species such as Vitellaria paradoxa and Parkia biglobosa, which are economically important, experienced the largest density reduction Trees density was also significantly higher in farms close to the monitoring roads used by park rangers to patrol the park. Farms that are far from the roads were monitored less frequently given that the number of park rangers declined over time. However, there was no significant variation in species richness and diversity over time, perhaps because of the low tree diversity in these systems. This masks evidences of species local extinctions. For example, species such as Pterocarpus erinaceus, Anogeissus leiocarpa, and Burkea africana which were present in the traditional agroforestry parklands in 2000 disappeared by 2016. This is associated with important land-use changes with conversion of gallery forests into cropland and wooded savannas indicating that human pressure not only affects species occurrence but also their habitats. Our study suggests that where land demand for agriculture is high, it is challenging for local people to maintain sustainable management practices in the absence of collective action.