Grazing lawns and overgrazing in frequently grazed grass communities. Issue 9 (13th September 2022)

• Record Type: Journal Article
• Authors: Hempson, Gareth P.; Parr, Catherine L.; Lehmann, Caroline E. R.; Archibald, Sally
• Is Part Of: Ecology and evolution. Volume 12:Issue 9(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-13
• Subjects: degradation -- environmental constraints -- grass traits -- growth forms -- palatability -- species composition; Ecology -- Periodicals; Evolution -- Periodicals; 577.05
• DOI: 10.1002/ece3.9268
• Languages: English
• ISSNs: 2045-7758

Abstract

Abstract: Frequent grazing can establish high forage value grazing lawns supporting high grazer densities, but can also produce overgrazed grass communities with unpalatable or low grass basal cover, supporting few grazers. Attempts to create grazing lawns via concentrated grazing, with a goal to increase grazer numbers, are thus risky without knowing how environmental conditions influence the likelihood of each outcome. We collected grass species and trait data from 33 frequently grazed grass communities across eastern South Africa (28 sites) and the Serengeti National Park, Tanzania (five sites), covering wide rainfall (336–987 mm year −1 ) and soil (e.g., 44%–93% sand) gradients. We identified four grass growth forms using hierarchical clustering on principal components analyses of trait data and assessed trait–environment and growth form–environment relationships using fourth corner and principal components analyses. We distinguished two palatable grass growth forms that both attract yet resist grazers and comprise grazing lawns: (1) "lateral attractors" that spread vegetatively via stolons and rhizomes, and (2) "tufted attractors" that form isolated tufts and may have alternate tall growth forms. By contrast, (3) tough, upright, tufted "resisters, " and (4) "avoiders" with sparse architectures or that grow appressed to the soil surface, are of little forage value and avoided by grazers. Grazing lawns occurred across a wide range of conditions, typically comprising lateral attractor grasses in drier, sandy environments, and tufted attractor grasses in wetter, low‐sand environments. Resisters occurred on clay‐rich soils in mesic areas, while avoiders were widespread but scarce. While grazing lawns can be established under most conditions, monitoring their composition and cover is important, as the potential for overgrazing seems as widely relevant. Tufted attractor‐dominated lawns appear somewhat more vulnerable to degradation than lateral attractor‐dominated lawns. Increased avoider and resister abundance both reduce forage value, although resisters may provide better soil protection. Abstract : Frequent grazing can convert grass communities into grazing lawns or into overgrazed areas, with strongly opposing consequences for the number of grazers the region can support. By examining the diversity of grass life histories and species composition in frequently grazed areas across broad rainfall and soil gradients, we find that grazing lawns can establish under most conditions, but that their form and resilience vary. Importantly, the potential for overgrazing is also widespread.