Mass sterilization of a common palm species by elephants in Kruger National Park, South Africa

Abstract

chronic herbivory by elephants rarely eliminates any species of woody savanna plants because these plants are typically vigorous basal resprouters after damage by fire or herbivory. In some instances, resprouting after elephant herbivory even increases stem numbers per unit area compared to protected areas. It is thus difficult to know whether an area has been severely degraded by elephant herbivory or not because although trees may be severely reduced in size, they will still be present and may even be relatively dense. By using an elephant exclosure in the Kruger national park, South Africa, we demonstrate that this resprouting ability masks the fact that entire populations of a widespread African palm, Hyphaene petersiana, are prevented from reaching sexual maturity by chronic elephant herbivory. Besides sterilizing these palms and thus preventing their evolution and seed dispersal, the absence of the palm fruits, flowers and tall stems has other negative biodiversity impacts on their associated fauna. We suggest that to determine sustainable elephant impacts on savanna plants, conservation managers also use the reproductive condition of savanna plants rather than their presence, height or stem density.

Heterogeneity in African savanna elephant distributions and their impacts on trees in Kruger National Park, South Africa

“…Instead, we may need to shift our focus to incorporate plants too. Savanna trees differ markedly in their growth rates and tolerance to herbivory (Midgley et al., 2020; Owen‐Smith et al., 2006; Staver et al., 2012; Wakeling et al., 2011), and as such, spatial variation in the ability of trees to tolerate and recover from elephant damage may obscure any relationship between where elephants are and where damage is observed (Fornoni et al., 2004; Więski & Pennings, 2014). Trees in areas densely populated by elephants may be locally adapted to avoiding or recovering from elephant damage, for example.…”

“…Elephants impact trees directly by stripping bark, breaking stems and branches, or simply uprooting trees entirely, all of which can make trees more susceptible to insect damage and fire‐induced mortality (Jacobs & Biggs, 2002; Moncrieff et al., 2017; Wigley et al., 2019). Some tree species are at particular risk (Duffy et al., 2002; Edkins et al., 2008; Midgley et al., 2020; Shannon et al., 2008), including Sclerocarya birrea (marula), Adansonia digitata (baobab), and Acacia nigrescens (alt. Senegalia nigrescens ; knobthorn), which are considered valuable ecologically and function as iconic species with touristic value (Owen‐Smith et al., 2006).…”

Reflecting on research produced after more than 60 years of exclosures in the Kruger National Park

“…vervet monkeys, porcupines, squirrels and wasps) and birds would nest within tall individuals (e.g. woodpeckers) (Midgley et al 2020). We suggest that these cascading effects on biodiversity may be true for any loss of plant species or reduction in vegetation structural diversity with herbivory, although the removal of herbivores may also result in the loss of dispersal opportunities for some species (Midgley, Gallaher & Kruger 2012).…”

“…Even when trees succeed through the recruitment bottleneck, persistent and chronic pruning of plants by elephants and other herbivores can result in mass sterilisation and a change in the adult population demography. From work that included the N'waswitshumbe exclosure, it was shown that most African palms (Hyphaene petersiana) in KNP are prevented from reaching sexual maturity and thus the ability to form seeds, because of chronic elephant herbivory (Midgley et al 2020).…”

What shapes the range edge of a dominant African savanna tree, Colophospermum mopane? A demographic approach

“…Insights from this can serve as a framework to understand the range limits of other dominant savanna species, particularly those that require a height threshold to produce seeds (Midgley et al, 2020;Wright et al, 2005). This approach points to mechanistic misunderstandings that can occur when using climate-based species distribution models as a tool to identify range limits in disturbance driven systems, something that is of increasing importance given our need to accurately predict the current and future ranges of plants under global change.…”