Grazing in a megagrazer-dominated savanna does not reduce soil carbon stocks, even at high intensities
Hyvarinen, Olli; te Beest, Mariska; le Roux, Elizabeth; Kerley, Graham I. H.; Findlay, Nicola; Schenkeveld, Walter D. C.; Trouw, Victor; Cromsigt, Joris P. G. M
(2023) Oikos, volume 2023, issue 9
(Article)
Abstract
Recent studies suggest that wild animals can promote ecosystem carbon sinks through their impacts on vegetation and soils. However, livestock studies show that intense levels of grazing reduce soil organic carbon (SOC), leading to concerns that rewilding with large grazers may compromise ecosystem carbon storage. Furthermore, wild grazers can both
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limit and promote woody plant recruitment and survival on savanna grasslands, with both positive and negative impacts on SOC, depending on the rainfall and soil texture contexts. We used grazing lawns in one of the few African protected savannas that are still dominated by megagrazers (> 1000 kg), namely white rhinoceros Ceratotherium simum, as a model to study the impact of prolonged and intense wild grazing on SOC stocks. We contrasted SOC stocks between patches of varying grazing intensity and woody plant encroachment in sites across different rhino habitat types. We found no differences in SOC stocks between the most- and least grazed plots in any of the habitats. Intermediately grazed plots, however, had higher SOC stocks in the top 5 cm compared to most and least grazed plots, but only in the closed-canopy woodland habitat and not in the open habitats. Importantly, we found no evidence to support the hypothesis that wild grazing reduces SOC, even at high grazing intensities by the world's largest megagrazer. Compared to the non-encroached reference plots, woody encroached plots had higher SOC stocks in soils with low clay content and lower SOC stocks in soils with high clay content, although only in the top 5 cm. Accordingly, our study highlights that wild grazers may influence SOC indirectly through their impact on tree-grass ratios in grassy ecosystems. Our study thus provides important insights for future natural climate solutions that focus on wild grazer conservation and restoration. Keywords: fire, grazing impact, rewilding, soil carbon, white rhinoceros, woody encroachment
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Keywords: fire, grazing impact, rewilding, soil carbon, white rhinoceros, woody encroachment, Landscape, African savanna, Land-use, Encroachment, Density, Park, Heterogeneity, Impacts, Dynamics, White rhinoceros, Ecology, Evolution, Behavior and Systematics
ISSN: 0030-1299
Publisher: Wiley
Note: Funding Information: – This research project was funded by the Swedish Research Council for Sustainable Development, Formas, under the project acronym Megaclim (diary no. 2017‐01000). ElR considers this work a contribution to her work on the WildSoil project funded by the Independent Research Fund Denmark (case number: 1127‐00046B). Funding Information: – We want to acknowledge Phumlani Zwane for his irreplaceable help in the field, together with the significant contributions by Ezemvelo KZN Wildlife staff including Dave Druce, Dlamini Falake, Eric Khumalo and Siphesihle Mbongwa. We are also grateful for the help of Elena van Doorn, Lawrence Steyn, Matti Meriläinen, Emilia Malmström, Daniel Gambra and Maja Widell during the soil sampling campaign. Finally, we want to thank Cedara Soil Fertility and Analytical Services Laboratory for their contributions to the soil analyses, and Jeppe Kristensen for sharing his knowledge about large herbivore impacts on soil carbon dynamics. – This research project was funded by the Swedish Research Council for Sustainable Development, Formas, under the project acronym Megaclim (diary no. 2017-01000). ElR considers this work a contribution to her work on the WildSoil project funded by the Independent Research Fund Denmark (case number: 1127-00046B). Publisher Copyright: © 2023 The Authors. Oikos published by John Wiley & Sons Ltd on behalf of Nordic Society Oikos.
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