Long-term vegetation changes in elephant-related areas of concern in Kruger National Park, South Africa

南非克鲁格国家公园与大象相关的关注区域的长期植被变化

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Abstract

African elephants, whether alone or in combination with other environmental factors such as floods, droughts, fire, and other herbivores, have significant impacts on large savanna trees, often contributing to declines over time. However, their effects on woody vegetation in general remain less well understood. To investigate these dynamics in a southern African savanna, we consulted park personnel in Kruger National Park to identify areas where woody cover loss had been observed and where elephants were believed to be the primary driver. Using a Global Ecosystem Dynamics Investigation (GEDI)-fusion remote sensing method, we then measured changes in woody cover and height across these areas from 2007 to 2022. Contrary to widespread concerns, GEDI-fusion data did not indicate a general decline in woody cover across the park. In fact, the overall trend shows an increase in woody vegetation. Nonetheless, some localized areas, which were flagged by park staff, showed declines in both general woody cover and large tree height, particularly along perennial rivers and on fertile soils. While we found no overall correlation between woody losses and increases in dry-season elephant densities across the study period, certain areas, especially those along perennial rivers, had the most notable increases in local elephant densities. To better isolate the role of fire, we overlaid woody cover losses with areas that experienced no fire during the study period (2.15% of pixels or ~40,000 ha). Notably, 44% of these fire-free areas overlapped with regions identified by park staff as of concern in terms of elephant-related impacts. While flood events may have contributed to tree losses in fire-free areas where these occur along perennial rivers, the findings collectively indicate that elephants-either independently or in combination with other factors-play a substantial role in the observed declines in woody cover and tree height in these areas. This study highlights the value of combining local knowledge and grassroots insights with advanced remote sensing techniques to detect and interpret spatial patterns of change. It also emphasizes the importance of targeted and adaptive management strategies in high-impact areas to reduce elephant-driven pressure on vulnerable vegetation and to support resilience across the broader landscape.

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