ECOLOGICAL INTERACTIONS BETWEEN HUMANS AND BAOBABS IN VELONDRIAKE, SOUTHWEST MADAGASCAR

In Madagascar, three of six endemic large-fruited baobab tree species (genus Adansonia) are currently classified by the IUCN as Endangered or Near Threatened, and the remaining species are experiencing population declines. Future climate shifts are expected to further reduce baobab species’ geographic range distributions unless these species can successfully disperse their seeds over larger distances. Though we know of extinct animals that Malagasy baobabs may have relied on for seed dispersal, the specific primary living disperser of these trees is unknown. On mainland Africa, there is evidence that humans have played a profound role in dispersing and maintaining baobab populations. On Madagascar, however, the role of human communities in shaping baobab distributions is poorly understood. Understanding interactions between humans and baobabs – both past and present – is essential for understanding the mechanisms that influence baobab distributions.

We hypothesize that humans may act as dispersers of baobabs in Madagascar, either directly through planting or indirectly through their herded zebu cattle. Here, we use spatial analysis of radiocarbon ages of modern baobab occurrences and archaeological sites to determine whether ecological interactions have occurred between humans and baobabs over the late Holocene in the Velondriake Marine Protected Area, Southwest Madagascar. We observe that areas where more archaeological material has been recovered positively correlate with areas with greater baobab density. Our results show strong associations between past human activity and baobabs, though it is difficult to determine whether humans planted baobabs or simply congregated near them. Additionally, we document evidence of past and present-day human usage of baobab bark across the Velondriake region and illuminate the relationship between bark usage and swirled patterns on baobab bark that indicate fungal disease. Our results suggest that modern communities in Southwest Madagascar may play a key role in the future conservation of baobabs.