Change in Mesoherbivore Browsing Is Mediated by Elephant and Hillslope Position

Abstract

Elephant are considered major drivers of ecosystems, but their effects within small-scale landscape features and on other herbivores still remain unclear. Elephant impact on vegetation has been widely studied in areas where elephant have been present for many years. We therefore examined the combined effect of short-term elephant presence (< 4 years) and hillslope position on tree species assemblages, resource availability, browsing intensity and soil properties. Short-term elephant presence did not affect woody species assemblages, but did affect height distribution, with greater sapling densities in elephant access areas. Overall tree and stem densities were also not affected by elephant. By contrast, slope position affected woody species assemblages, but not height distributions and densities. Variation in species assemblages was statistically best explained by levels of total cations, Zinc, sand and clay. Although elephant and mesoherbivore browsing intensities were unaffected by slope position, we found lower mesoherbivore browsing intensity on crests with high elephant browsing intensity. Thus, elephant appear to indirectly facilitate the survival of saplings, via the displacement of mesoherbivores, providing a window of opportunity for saplings to grow into taller trees. In the short-term, effects of elephant can be minor and in the opposite direction of expectation. In addition, such behavioural displacement promotes recruitment of saplings into larger height classes. The interaction between slope position and elephant effect found here is in contrast with other studies, and illustrates the importance of examining ecosystem complexity as a function of variation in species presence and topography. The absence of a direct effect of elephant on vegetation, but the presence of an effect on mesoherbivore browsing, is relevant for conservation areas especially where both herbivore groups are actively managed.

Severe drought limits trees in a semi‐arid savanna

“…Mesoherbivores such as impala have been shown to avoid elephants (Lagendijk et al. ), such that impala probably concentrate in the partial exclosure, perhaps more so during the drought, given heightened elephant activity near rivers in drought years (Shannon et al. ; this experiment is located near the banks of the Sabie River).…”

“…This may be spurious or may reflect a real combination of mesoherbivore displacement and herbivore diet-switching under drought conditions. Mesoherbivores such as impala have been shown to avoid elephants (Lagendijk et al 2015), such that impala probably concentrate in the partial exclosure, perhaps more so during the drought, given heightened elephant activity near rivers in drought years (Shannon et al 2013; this experiment is located near the banks of the Sabie River). Meanwhile, impala, a mixed-feeding species, switched to eating a substantially higher proportion of trees during the drought (Abraham et al 2019), potentially increasing tree mortality in the partial exclosure.…”

Fine‐scale habitat heterogeneity influences browsing damage by elephant and giraffe

“…However, the “browse trap” for these smaller herbivores is shorter than that of megaherbivores and trees may easily escape it, thus remaining only vulnerable to megaherbivore browsing (Augustine & McNaughton, 2004). Browsing effects by megaherbivores may either benefit these smaller herbivores by maintaining tree canopies at lower accessible heights (Kohi et al., 2011) or may intensify competition for forage resources (Lagendijk et al., 2015).…”

“…Usually browsing pressure within an habitat is positively correlated with the amount of time animals spend in an area (Bond & Loffell, 2001; Milligan & Koricheva, 2013), but the factors that influence foraging decisions vary remarkably across herbivore species and over time (Fortin et al., 2015; Lagendijk et al., 2015; Stephens, 2008). For megaherbivores, movement patterns are driven more by maximizing forage intake and minimizing energy expenditure rather than avoiding predators (Riginos, 2015; Sinclair, Mduma, & Brashares, 2003).…”

No evidence for an elephant-termite feedback loop in Sand Forest, South Africa

“…Cumming et al, 1997;Kerley et al, 2008;Lagendijk et al, 2012). Some positive effects of elephant have been documented, such as an increase in lizard densities in elephant-impacted trees (Pringle, 2008), as well as (short-term) neutral effects on woody species assemblages (Lagendijk et al, 2015). In light of the current elephant debate in southern Africa (i.e.…”