Mitigating bush encroachment via habitat manipulation: Ecological cascade effects

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Melissa Schmitt

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African savannas are characterized by a mosaic of trees and grass. The ratio of trees and grasses exists along a continuous gradient in savannas, resulting in savannas that range from open, grassy savannas to denser, closed-canopy savannas. However, climate change is leading to woody thickening in African savannas, and predictions suggest that by 2100 savannas will become forests, thereby threatening the ecosystem services provided by savannas. To combat this woody thickening, many land managers across South Africa have implemented large-scale (>100 ha), decades-long tree clearing in an effort to maintain areas of low tree densities. However, the implications of these habitat manipulations for herbivore communities are unknown. Thus, we aimed to identify how tree clearing influenced herbivore community composition. We used herbivore counts from survey data collected in a South African savanna from both the wet and dry seasons that link with savanna vegetation structure (i.e. tree-grass ratio). We used model-based clustering to identify unique herbivore-vegetation structure states. The model-based clustering revealed that both bush encroached areas and large-scale tree cleared areas result in states that have depauperate wildlife communities compared to intermediate woody states. This suggests that both the effects of bush encroachment and the implemented management practices have similar, negative effects for herbivores. Thus, to restore savanna ecosystem functioning, our results suggest that degraded, cleared areas should be restored and that savanna management should strive to maintain an intermediate woody density

Resource Type:
Audio/Video, Conference Presentation, SER2019

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Society for Ecological Restoration