Grazing and Conservation Management

Volume 11 of the series Conservation Biology Series pp 137-184

The impact of grazing on plant communities

  • Jan P. BakkerAffiliated withLaboratory of Plant Ecology, University of Groningen

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The simplest way to discuss the effects of grazing on plant communities is to compare grazed and ungrazed situations. The results of a number of studies in which large herbivores were excluded from previously grazed landscapes/plant communities are summarized in Table 5.1. This list is certainly not complete but it allows some generalizations. Grazed areas harbour pioneer species, including annuals and biennials that have to establish from seedlings, low-stature species and rosette plants. A similar conclusion was reached by Scherfose (1993) in a literature review on the impact of grazing on plant species in salt marshes in the Wadden Sea area. The ratio of species suffering from grazing and species promoted by grazing turned out to be about 1: 1 at the lower and middle salt marsh. At the higher salt marsh more species were promoted by than suffering from grazing. After the exclusion of grazing, the aforementioned groups of species are often replaced by tall grasses and herbs accompanied by litter accumulation, and by shrubs and trees. The general pattern shows a higher above-ground standing crop M exclosures than in continuously grazed plots, as reported in a review by Milchunas and Lauenroth (1993).