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ARS Home » Plains Area » Fort Collins, Colorado » Center for Agricultural Resources Research » Rangeland Resources & Systems Research » Research » Publications at this Location » Publication #361354
Title: Large herbivores maintain a two-phase herbaceous vegetation mosaic in a semi-arid savanna

Author
item Augustine, David
item WIGLEY, BEN - Nelson Mandela African Institute Of Science And Technology
item RATNAM, JAYASHREE - National Centre For Biological Sciences
item KIBET, STALINE - University Of Nairobi
item NYANGITO, MOSES - University Of Nairobi
item SANKARAN, MAHESH - National Centre For Biological Sciences

Submitted to: Ecology and Evolution
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/2019
Publication Date: 11/22/2019
Citation: Augustine, D.J., Wigley, B., Ratnam, J., Kibet, S., Nyangito, M., Sankaran, M. 2019. Large herbivores maintain a two-phase herbaceous vegetation mosaic in a semi-arid savanna. Ecology and Evolution. 9:12779-12788. https://doi.org/10.1002/ece3.5750.
DOI: https://doi.org/10.1002/ece3.5750

Interpretive Summary: Rangelands around the world often have patches of bare soil of varying sizes. Whether grazing by domestic livestock is a factor influencing the size, pattern, and persistence of these patches is often debated, especially in dry zones of the world where rainfall and runoff alone could be the primary factor preventing plants from fully occupying space. We report on a long-term (17 yr) grazing removal experiment in a semi-arid savanna where large (>10 square yard) patches of bare soil were interspersed with the native grasses. Short term (3 yr) grazing removal did not allow bare patches to become revegetated, whereas following long-term (17 yr) grazing removal, bare soil patches were revegetated by a diverse community of grasses. Our results show that grazing does indeed alter the balance between bare and vegetated patches, and affect the types of grasses dominating both patch types in this semiarid savanna. However, bare patches within this mosaic can recover if grazing is removed for a sufficently long time.

Technical Abstract: Many arid and semi-arid rangelands exhibit distinct spatial patterning of vegetated and bare-soil-dominated patches, where the latter potentially represents a degraded ecosystem state. The degree to which grazing contributes to the formation or maintenance of degraded patches has been widely discussed and modelled, but empirical studies of the role of grazing in their formation, persistence, and reversibility are limited. Here, we report on a long-term (17 yr) grazing removal experiment in a semi-arid savanna where vegetated patches composed of perennial grasses were interspersed within large (>10 m2) patches of bare soil. Short term (3 yr) grazing removal did not allow bare patches to become revegetated, whereas following long-term (17 yr) 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 the establishment of tufted bunchgrasses. Our results show that grazers alter the balance between bare and vegetated patches, and affect the types of grasses dominating both patch types in this semiarid savanna. Thus, 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.