A Meta‐Analysis of the Impact of African Elephants on Savanna Vegetation

Abstract

Large herbivores such as elephants (Loxodonta africana) apparently have a negative impact on woody vegetation at moderate to high population densities. The confounding effects that fire, drought, and management history have may complicate assignment of such impacts to herbivory. We reviewed 238 studies published over 45 years and conducted a meta‐analysis based on 21 studies that provided sufficient information on response of woody vegetation to elephants. We considered size and duration of studies, elephant densities, rainfall, fences, and study outcomes in our analysis. We detected a disproportionate citation of 20 published studies in our database, 15 of which concluded that woody vegetation responded negatively to elephants. Our analysis showed that high elephant densities had a negative effect on woody vegetation but that rainfall and presence of fences influenced these effects. In arid savannas, woody vegetation always responded negatively to elephants. In transitional savannas, an increase in elephant densities did not influence woody vegetation response. In mesic savannas, negative responses of woody vegetation increased when elephants occurred at higher densities, whereas elephants confined by fences also had more negative effects on woody plants than elephants that were not confined. Our analysis suggested that rainfall and fences influenced elephant density related impact and that research results were often site‐specific. Local environmental conditions and site‐specific objectives should be considered when developing management actions to curb elephant impacts on woody vegetation.

History of Animals using Isotope Records (HAIR): A 6-year dietary history of one family of African elephants

“…In many ecosystems, elephant range restriction concentrates and amplifies impacts of elephants on vegetative communities, leading to effects on species composition across trophic levels (43,44). With climate models predicting greater variation in annual rainfall in Eastern Africa (45), the dynamics between elephant populations and their environments are likely to be strongly regulated by the relationship between climatic fluctuation and diet.…”

Elephant-mediated habitat modifications and changes in herbivore species assemblages in Sabi Sand, South Africa

“…2 Relationship between the elephant density (N/km 2 ) and the overall tree stem density (N/km 2 ) (a), the number of stems per tree (b) and the estimated total consumption of browse (filled squares) and grass (open squares) of the relevant herbivores depicted as a percentage of the total consumption excluding elephants in Sabi Sand WildtuinMalaMala complex (c) (Fritz et al 2002;Kohi et al 2011;Valeix et al 2011;Kohi 2013). The impact of elephant may be site-or contextdependent (Guldemond and Van Aarde 2008) and varies spatially within KNP (Eckhardt et al 2000). Elephant numbers in the Sabi Sand Wildtuin-MalaMala complex were strongly negatively correlated with densities of both small and large trees.…”

“…In the proximity of large perennial rivers, current elephant densities in the KNP exceed 1.5 animals/km 2 (Smit and Ferreira 2010). Elephant impacts can also vary spatially and can be site-or context-dependent (Eckhardt et al 2000;Guldemond and Van Aarde 2008). Communicated by M. Scandura This impact of elephants on trees in the system has raised the concern of scientists and managers alike (Whyte et al 1998;Van Aarde et al 1999;Van Aarde et al 2006;Kerley et al 2008), as the decline in woody cover could negatively affect the browsing species in the system.…”

Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA)

“…Skarpe et al 2004;OwenSmith 2006;Guldemond and van Aarde 2008;Cowling et al 2009;Goheen et al 2009;Luske et al 2009;Mapaure and Moe 2009). The simple act of walking would have compacted or disrupted soil and disturbed the herb and shrub strata of the vegetation (Butler 1995), as well as any cryptobiotic soil textures that might have developed on Morrison dryland soils, and the large footprints of sauropods probably created microhabitats for small organisms different from those in undisrupted soils (cf.…”