@article {164787, title = {Responses of African Savanna Trees to Large Herbivore Extinction and Rewilding.}, journal = {Ecol Lett}, volume = {29}, year = {2026}, month = {2026 Mar}, pages = {e70360}, abstract = {

The global decline or extinction of large mammals over the last 50,000 years has caused sweeping changes in the ecosystems they once inhabited. Trophic rewilding holds promise for returning lost ecological function and restoring processes that support ecosystem resilience, but there remains considerable uncertainty surrounding the efficacy of rewilding. To address this uncertainty, we experimentally excluded a diverse African savanna mammal community from replicated plots for 18 years to simulate extinction. Herbivore exclusion caused a rapid increase in tree cover, which was underlain by shifts in community composition and increases in canopy area, growth rate and density. We then removed the exclosure fences, simulating rewilding. Reintroducing herbivores rapidly reduced tree cover and largely reversed individual phenotypic shifts, but tree density remained elevated despite increased mortality rates after reintroduction. Our results suggest that even short-term extirpation can cause complex shifts in vegetation communities, some of which may be resistant to rewilding.

}, keywords = {Africa, Animals, Conservation of Natural Resources, Extinction, Biological, Grassland, Herbivory, Mammals, Trees}, issn = {1461-0248}, doi = {10.1111/ele.70360}, url = {https://onlinelibrary.wiley.com/doi/10.1111/ele.70360}, author = {Coverdale, Tyler C and Sankaran, Mahesh and Davies, Andrew B and Ratnam, Jayashree and Wigley, Benjamin J and Augustine, David J} } @article {73041, title = {Grasses continue to trump trees at soil carbon sequestration following herbivore exclusion in a semi-arid African savanna.}, journal = {Ecology}, year = {2020}, month = {2020 Feb 06}, pages = {e03008}, abstract = {

While studies have shown that mammalian herbivores often limit aboveground carbon storage in savannas, their effects on belowground soil carbon storage remains unclear. Using three sets of long-term, large herbivore exclosures with paired controls, we asked how almost two decades of herbivore removal from a semi-arid savanna in Laikipia, Kenya affected aboveground (woody and grass) and belowground soil carbon sequestration, and determined the major source (C vs. C ) of belowground carbon sequestered in soils with and without herbivores present. Large herbivore exclusion, which included a diverse community of grazers, browsers, and mixed-feeding ungulates, resulted in significant increases in grass cover (~22\%), woody basal area (~8 m ha ) and woody canopy cover (31\%), translating to a ~8.5 t ha increase in aboveground carbon over two decades. Herbivore exclusion also led to a 54\% increase (20.5 t ha ) in total soil carbon to 30 cm depth, with ~71\% of this derived from C grasses (vs. ~76\% with herbivores present) despite substantial increases in woody cover. We attribute this continued high contribution of C grasses to soil C sequestration to the reduced offtake of grass biomass with herbivore exclusion together with the facilitative influence of open sparse woody canopies (e.g. Acacia spp.) on grass cover and productivity in this semi-arid system.

}, issn = {1939-9170}, doi = {10.1002/ecy.3008}, author = {Wigley, Benjamin J and Augustine, David J and Coetsee, Corli and Ratnam, Jayashree and Sankaran, Mahesh} } @article {69322, title = {Large herbivores maintain a two-phase herbaceous vegetation mosaic in a semi-arid savanna.}, journal = {Ecol Evol}, volume = {9}, year = {2019}, month = {2019 Nov}, pages = {12779-12788}, abstract = {

Many arid and semi-arid rangelands exhibit distinct spatial patterning of vegetated and bare soil-dominated patches. The latter potentially represent a grazing-induced, degraded ecosystem state, but could also arise via mechanisms related to feedbacks between vegetation cover and soil moisture availability that are unrelated to grazing. The degree to which grazing contributes to the formation or maintenance of degraded patches has been widely discussed and modeled, but empirical studies of the role of grazing in their formation, persistence, and reversibility are limited.We report on a long-term (17\ years) grazing removal experiment in a semi-arid savanna where vegetated patches composed of perennial grasses were interspersed within large (\>10\ m) patches of bare soil.Short-term (3\ years) grazing removal did not allow bare patches to become revegetated, whereas following long-term (17\ years) grazing removal, bare soil patches were revegetated by a combination of stoloniferous grasses and tufted bunchgrasses. In the presence of grazers, stoloniferous grasses partially recolonized bare patches, but this did not lead to full recovery or to the establishment of tufted bunchgrasses.These results show that grazers alter both the balance between bare and vegetated patches, as well as the types of grasses dominating both patch types in this semiarid savanna.Synthesis: Large herbivores fundamentally shaped the composition and spatial pattern of the herbaceous layer by maintaining a two-phase herbaceous mosaic. However, bare patches within this mosaic can recover given herbivore removal over sufficiently long time scales, and hence do not represent a permanently degraded ecosystem state.

}, issn = {2045-7758}, doi = {10.1002/ece3.5750}, author = {Augustine, David J and Wigley, Benjamin J and Ratnam, Jayashree and Kibet, Staline and Nyangito, Moses and Sankaran, Mahesh} } @article {35150, title = {Defence strategies in African savanna trees.}, journal = {Oecologia}, year = {2018}, month = {2018 May 12}, abstract = {

Southern African savannas are commonly polarised into two broad types based on plant functional types and defences; infertile savannas dominated by broad-leaved trees typically defended by nitrogen-free secondary compounds and fertile savannas dominated by fine-leaved trees defended by structural defences. In this study, we use trait and other data from 15 wooded savanna sites in Southern Africa and ask if broad-leaved and fine-leaved species dominate on nutrient-poor and nutrient-rich soils, respectively. We then test if there is there any evidence for trade-offs in chemical (i.e., condensed tannins and total polyphenols) vs. structural defences on different soil types. We did not find strong evidence for a general divide in fine- vs. broad-leaved savannas according to soil fertility, nor for a simple trade-off between chemical and structural defences. Instead, we found savanna species to cluster into three broad defence strategies: species were high in leaf N and either (A) highly defended by spines and chemicals or (B) only structurally defended, or (C) low in leaf N and chemically defended. Finally, we tested for differences in browser utilisation between soil types and among plant defence strategies and found that browsing by meso-herbivores was higher on nutrient-rich soils and targeted species from groups A and B and avoided C, while browsing by elephants was mostly not affected by soil type or defence strategy. We propose a framework that can be used as a basis for asking strategic questions that will help improve our understanding of plant defences in savannas.

}, issn = {1432-1939}, doi = {10.1007/s00442-018-4165-8}, author = {Wigley, Benjamin J and Fritz, Herv{\'e} and Coetsee, Corli} }