Roads disrupt seed dispersal in animal-mediated plants in an Amazonian rainforest

Background/Question/Methods: Ecological interactions are being affected at unprecedented rates by human activities in tropical forests. Yet, the continuity of ecological functions such as seed dispersal is crucial for forest regeneration. It thus becomes increasingly urgent to be able to rapidly assess the health status of these processes in order to take appropriate management measures. Using a new method that we developed to rapidly assess the level of seed removal and frugivore activity, we aimed at evaluating the effect on the health status of the nearby mature forest of a recently-open road in Guyane. We studied the level of fruit consumption and seed dispersal for four animal-dispersed tree species, scattered in forest corridors and further away along the 50-km road. We counted fallen fruit, fruit valves, and seeds of focal fruiting tree species (N = 30-36 trees per genus) in single 1 m² quadrats, and calculated the proportion of fruits opened and consumed, and the proportion of seeds removed by animals. In addition to direct visual sightings during samplings, we used automatic remote cameras to identify the ground-dwelling wildlife during fruiting periods in the forest nearby the road.

Results/Conclusions: Our results showed that the proportion of fruits opened and consumed, and the level of seeds removed in the forest within the vicinity (< 1-2 km) of the road is ca. 30-50% lower than previous observations carried out at a remote control forest (Natural Reserve of Nouragues). Our indices also confirm that large birds (toucans) and small body-sized primates are the main consumers and seed dispersers remaining in the forest nearby the road. We also show that the primates-specialist tree species are more affected by road proximity than vertebrates-generalist tree species thanks to some compensatory effects by birds when large primates are barely present. Therefore, despite effort to preserve forest continuity (vegetation bridge over the asphalted road), increased hunting pressures in forest nearby road remain the main driver of defaunation which has affected ecological processes such as seed dispersal less than a decade after the road was opened to traffic.