Abstract
Forest edges that border savanna are dynamic features of tropical landscapes. Although the role of fire in determining edge dynamics has been relatively well explored, the role of mega-herbivores, specifically elephants, has not received as much attention. We investigated the role of forest elephants in shaping forest edges of the forest–savanna mosaic in Lopé National Park, Gabon. Using forty camera traps, we collected 1.2 million images between May 2016 and June 2017. These images were classified by over 10,000 volunteers through an online citizen science platform. These data were combined with a 33-year phenology dataset on elephant-favoured fruiting tree species, and field measurements of elephant browsing preferences and damage. Our results showed a strong relationship between forest elephant density at the forest edge and fruit availability. When fruit availability was high, elephant density at the edge reached values nearly double the highest densities ever reported in any other part of the landscape (7.5 elephants km−2 in this study vs the previous highest estimate of 4 elephants km−2). The highest elephant densities occurred at the end of the dry season, but even outside of this high density period elephant density at the forest edge (2.4 elephants km−2) was more than double what other studies estimate for forest interiors with low human hunting pressure (1 elephant km−2). We found forest elephants to be selective browsers, but their browsing was non-destructive (in contrast to savanna elephants) and had little effect on tree size demography. Elephant paths acted as firebreaks during savanna burning, making them inadvertent protectors of the fire-sensitive forest and contributing to the stabilising feedbacks that allow forest and savanna to coexist in tropical landscapes.
Highlights
Elephants are the largest living mega-herbivore and have significant impacts on the ecosystems they inhabit
We investigated the role of forest elephants in shaping forest edges of the forest– savanna mosaic in Lope National Park, Gabon
Our results showed a strong relationship between forest elephant density at the forest edge and fruit availability
Summary
Elephants are the largest living mega-herbivore and have significant impacts on the ecosystems they inhabit. African elephants form two genetically and ecologically distinct groups (Rohland and others 2010; Maisels and others 2013): the savanna elephant, Loxodonta africana (Blumenbach, 1797) and the physically smaller forest elephant, L. cyclotis (Matschie, 1900). Both African elephant species have faced drastic population declines, recently the most severe of these has been experienced by the forest elephants of Central Africa (Maisels and others 2013; Poulsen and others 2017). What this loss means for ecosystem functionality is not well understood, as relatively little is known about forest elephants relative to savanna elephants (Poulsen and others 2018). A better understanding of forest elephant ecology could galvanise greater support for their urgent protection
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