Differential herbivore occupancy of fire-manipulated savannas in the Satara region of the Kruger National Park, South Africa

Abstract

Fire has long been considered an essential determinant of vegetation structure in savanna ecosystems (Sankaran & Hanan 2008:17) and is frequently utilised as a management tool by conservationists. Changes in fire management in southern Africa over the past century reflect an increasing level of ecological consideration (Van Wilgen 2009:105), partially through the insight of manipulations such as the experimental burn plots (EBPs) in the Kruger National Park (KNP), South Africa. This fire experiment began in 1954 (Biggs et al. 2003:46) and has facilitated research projects on fire ecology in savanna ecosystems (Govender, Trollope & Van Wilgen 2006:43). Fire extent, frequency and burn shape influence wildlife distributions across landscapes (Cromsigt, Archibald & Owen-Smith 2017:47; Roberts 2008:1). Moreover, spatially patchy fire drives the spatial and temporal distribution of grazers, in particular, to congregate on immediate post-fire patches (McGranahan & Kirkman 2013:176). Burning affects forage quality and quantity as well as animal behaviour and diet (Roberts 2008:1). Fire frequency further influences ungulate distribution through altered predation risk (Burkepile et al. 2013:139). At a landscape scale, fire reduces plant biomass (Hanan et al. 2008:171), resulting in temporary displacement of herbivores. Fire affects nutrient cycling (Van der Vijver, Proot & Prins 1999:173) and soil organic nitrogen and carbon (Holdo et al. 2009:115), which influence The Kruger National Park’s (KNP) long-running experimental burn plots (EBPs) have a history of research projects, which improve the understanding of fire in savanna ecosystems. Using data from KNP’s aerial censuses (2005–2016) and in situ dung count data (2008–2017), this study assessed (1) herbivore densities on the Satara, N’Wanetsi and Marheya EBPs, on annual, triennial and no-burn treatments and across pre-, during and post-drought climate conditions; (2) herbivore densities of these EBPs relative to their non-manipulated surroundings and (3) the extent to which distance to water and rainfall influence ungulate densities. The results revealed that herbivore mean density differed significantly between the three EBPs of Satara and across their fire treatments. N’Wanetsi showed the highest density (0.30 animals/ha), whilst the lowest was found at Marheya (0.12 animals/ha). Overall, pre-drought density was higher on the annual plots (0.56 animals/ha), whilst higher post-drought density was evidenced on the triennial plots (0.80 animals/ha). On average, there were significantly higher herbivore densities on the EBPs (2.54 animals/ha) compared to the surrounding matrix at the larger scales of the Satara management section (0.15 animals/ha) and the central KNP (0.18 animals/ha). A positive correlation between herbivore mean density estimate and distance to water was shown. However, grazer mean density across fire treatments was strongly correlated to rainfall.