Hunting and logging, the most ubiquitous human disturbances in tropical forests, fundamentally alter populations and communities. Hunting-induced population declines in seed-dispersing vertebrate communities may reduce the average dispersal distances of the tree species that rely on them. Declines in dispersal distance change Janzen-Connell effects, including density-dependent mortality. At the same time, selective logging practices using heavy machinery to harvest marketable species kills collateral trees, compacts soils, and may alter competitive interactions by removing canopy trees. Taken together, these disturbances are changing community composition of tropical forests in ways that are poorly understood, with implications for carbon storage, biodiversity conservation, and ecosystem function. We present a novel state-space model for estimating tree fecundity and seed dispersal through space using three years of seed rain data collected from a large-scale observational experiment in logged, hunted, and pristine forests in northern Republic of Congo.
Results/Conclusions
We find that tree fecundity is improved by logging, but that the benefits of increased seed production is offset by the effects of hunting. We evaluated if the magnitudes of increased dispersal with logging could be linked to the different dispersal modes. Contrary to our expectations, we did not find a consistent effect of dispersal vector on dispersal distances for disturbance regimes, possibly reflecting the numbers and complexity of dispersal vectors employed by tropical tree species. A quarter of the abundant species in our seed data belonged to lianas, an important and understudied group of angiosperms not represented in most forest censuses, in some cases due to their small diameters. By omitting this plant form, forest inventories may systematically underestimate their importance for trophic cascades, ecological services, and interactions with other forest trees.