Assessing the effects of elephant foraging on the structure and diversity of an Afrotropical forest

African forest elephants (Loxodonta cyclotis) are ecosystem engineers that
browse and damage large quantities of vegetation during their foraging and
movement. Though elephant trail networks and clearings are conspicuous
features of many African forests, the consequences of elephant foraging
for forest structure and diversity are poorly documented. In this study in
northeastern Gabon, we compare stem size, stem density, proportional
damage, species diversity, and species relative abundance of seedlings and
saplings in the vicinity of seven tree species that produce
elephant-preferred fruits (“elephant trees”) relative to control trees
that do not. Across 34 survey trees, with a combined census area of 2.04
ha, we recorded data on 26,128 woody stems in three sizes classes.
Compared to control trees, the area around elephant trees had: a) a
significantly greater proportion of damaged seedlings and a marginally
greater proportion of damaged saplings (with 82% and 24% greater odds of
damage, respectively); b) no significant difference in stem density or
species diversity; and c) a significantly greater relative abundance of
seedlings of elephant tree species. Increasing distance away from focal
elephant trees was associated with significantly reduced sapling stem
damage, significantly increased sapling stem density, and significantly
increased sapling species diversity. Considered in sum, our results
suggest that elephants can affect the structure and diversity of
Afrotropical forests through their foraging activities, with some
variation based on location and plant size class. Developing a more
complete understanding of elephants’ ecological effects will require
continued research, ideally with manipulative experiments.