Understanding Long-Term Variations in an Elephant Piosphere Effect to Manage Impacts

Abstract

Surface water availability is a key driver of elephant impacts on biological diversity. Thus, understanding the spatio-temporal variations of these impacts in relation to water is critical to their management. However, elephant piosphere effects (i.e. the radial pattern of attenuating impact) are poorly described, with few long-term quantitative studies. Our understanding is further confounded by the complexity of systems with elephant (i.e. fenced, multiple water points, seasonal water availability, varying population densities) that likely limit the use of conceptual models to predict these impacts. Using 31 years of data on shrub structure in the succulent thickets of the Addo Elephant National Park, South Africa, we tested elephant effects at a single water point. Shrub structure showed a clear sigmoid response with distance from water, declining at both the upper and lower limits of sampling. Adjacent to water, this decline caused a roughly 300-m radial expansion of the grass-dominated habitats that replace shrub communities. Despite the clear relationship between shrub structure and ecological functioning in thicket, the extent of elephant effects varied between these features with distance from water. Moreover, these patterns co-varied with other confounding variables (e.g. the location of neighboring water points), which limits our ability to predict such effects in the absence of long-term data. We predict that elephant have the ability to cause severe transformation in succulent thicket habitats with abundant water supply and elevated elephant numbers. However, these piosphere effects are complex, suggesting that a more integrated understanding of elephant impacts on ecological heterogeneity may be required before water availability is used as a tool to manage impacts. We caution against the establishment of water points in novel succulent thicket habitats, and advocate a significant reduction in water provisioning at our study site, albeit with greater impacts at each water point.

Plant species composition and diversity depending on piospheres and seasonality in the southern rangelands of Kenya

“…Piospheric studies on species composition, richness, and diversity indices have been done in most parts of the world including Australia (Landman et al 2012), Asia (Shahriary et al 2012), Southern Africa (Todd 2006), Northern Africa (Tarhouni et al 2007), and Uganda (Egeru 2014;Egeru et al 2015). Nevertheless, there have been no studies conducted in Kenya, especially in the southern rangelands where water interventions have been widely undertaken to alleviate water shortage and enhance pastoral livelihoods (Opiyo et al 2015).…”

Piospheric influence on forage species composition and abundance in semi-arid Karamoja sub-region, Uganda

“…The availability of any one of these resources at any given location in a semi-arid landscape will determine the level of herbivore influence on vegetation dynamics at both spatial and temporal scales (Yu and Wu 2010;Wesuls et al 2013). The intensity of herbivore influence is dependent on the spatio-temporal patterns of foraging decisions (Landman et al 2012). Proximity to water, topography and the availability of food have been identified as key determinants of foraging decisions at landscape level (Bailey and Provenza 2008;Ash et al 2004).…”

“…Proximity to water, topography and the availability of food have been identified as key determinants of foraging decisions at landscape level (Bailey and Provenza 2008;Ash et al 2004). These foraging decisions have impacts on biological diversity because herbivore foraging affects various aspects of vegetation dynamics (Landman et al 2012). Further, adaptive components such as deferred resting of grazing sites to protect forage plants during critical life stages are important in influencing vegetation dynamics (Linstädter et al 2013).…”

“…Piosphere influence resulting from activity gradients has been largely studied with a focus on large herbivores such as elephants (Landman et al 2012;Sternberg 2012). Distance-dependent effects including declines in perennial plants and species richness as well as structural diversity of perennial plants have been observed (Brooks et al 2006;Landman et al 2012).…”

Effect of piospheres on physio-chemical soil properties in the Southern Rangelands of Kenya

“…Several studies have revealed that piospheres, created to curb water scarcity in most rangelands across the world, have adverse effects on both soil and vegetation (Brooks and Matchett 2006;Landman et al 2012;Shahriary et al 2012).…”