Individual study: Site productivity and plant size explain the response of annual species to grazing exclusion in a Mediterranean semi-arid rangeland
Osem Y., Perevolotsky A. & Kigel J. (2004) Site productivity and plant size explain the response of annual species to grazing exclusion in a Mediterranean semi-arid rangeland. Journal of Ecology, 92, 297-309
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Other biodiversity: Exclude grazers
A replicated, controlled study in 1996–1999 in shrublands in Israel (same study as (14)) found that total plant cover increased with grazer exclusion, and plant communities differed between plots with or without grazers excluded. Differences depended on the productivity of the site. Plants: Total plant abundance was higher in plots with grazers excluded, compared to grazed plots (data reported as model results). There were bigger differences in plant communities between ungrazed and grazed plots in more productive areas (data reported as Sorenson’s quantitative similarity index). Of the 36 most common annual plants, 20 showed a response to grazer exclusion: 11 species increased after grazer exclusion (only in low-productivity sites, in two of 11 species); seven species decreased (only in high-productivity sites, in one of seven species); and two species decreased in high-productivity sites but increased in low-productivity sites. Overall, more species increased than decreased in low-productivity sites (6–11 vs 1–2 species), but the opposite was true in high productivity sites (6 vs 15). Generally, large species were more abundant in ungrazed plots, compared to grazed plots (15% vs 9% relative abundance), smaller species were less abundant (54% vs 63%), and medium species showed variable responses (20% in both). These responses were more pronounced in high-productivity sites. Methods: Four 10 x 10 m plots from which sheep were excluded were established in 1993 in each of four sites, differing in topography and productivity. Vegetation samples were collected in April 1996–1999.