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Grazing by livestock is used as a management tool to prevent the dominance of a single tall-growing specises during succession
on European salt marshes. The effects of natural small herbivores are often neglected by managers. Long-term exclosure experiments
on the island of Schiermonnikoog show that hares retard vegetation succession at the early stages of salt-marsh development.
In the present study we test whether we can scale-up these exclosure studies to a whole salt-marsh system. We compared 30
years of undisturbed vegetation succession at the Wadden Sea islands of Schiermonnikoog, Rottumerplaat (both The Netherlands)
and Mellum (Germany). Salt-marsh development started at all sites in the early 1970s. Hares have been present only on Schiermonnikoog.
At each site an area was selected covering a gradient from high to low salt marsh. Surface elevation and clay thickness were
measured and a vegetation map was made on the three islands. The areas showed similar clay thickness at low surface elevation,
indicating similar sedimentation ratesand hence nitrogen inputs. Rottumerplaat and Mellum showed a higher dominance of the
late successional speciesAtriplex portulacoides in the low marsh andElymus athericus in the high marsh compared to Schiermonnikoog. Typical mid-successional, important food plant species for hares and geese
had a higher abundance at Schiermonnikoog. Patterns of vegetation development in the absence of hares followed the observed
patterns in the smallscale exclosure experiments at Schiermonnikoog. Without hare grazing, vegetation succession proceeds
more rapidly and leads to the dominance of tall-growing species in earlier stages of succession. The present study shows that
next to large herbivores, small herbivores potentially have largescale effects on salt-marsh vegetation succession during
the early successional stages. 相似文献
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The Effects of Long-Term Grazing Exclosures on Range Plants in the Central Anatolian Region of Turkey 总被引:1,自引:0,他引:1
Over the last fifty years, almost half of the steppe rangeland in the Central Anatolian Region of Turkey (CAR) has been converted
to cropland without an equivalent reduction in grazing animals. This shift has led to heavy grazing pressure on rangeland
vegetation. A study was initiated in June 2003 using 6 multiscale Modified-Whittaker plots to determine differences in plant
composition between areas that have not been grazed in 27 years with neighboring grazed plant communities. A total of 113
plant species were identified in the study area with the ungrazed plots containing 32 plants more than the grazed plots. The
major species were Astragalus acicularis, Bromus tomentellus, Festuca valesiaca, Genista albida, Globularia orientalis, Poa bulbosa, and Thymus spyleus ssp rosulans. Grazing impacts on forbs were more pronounced than for grasses and shrubs. Based on Jaccard’s index, there was only a 37%
similarity of plant species between the two treatments. Our study led to four generalizations about the current grazing regime
and long-term exclosures in the steppe rangeland around the study area: (1) exclosures will increase species richness, (2)
heavy grazing may have removed some plant species, (3) complete protection from grazing for a prolonged period of time after
a long history of grazing disturbance may not lead to an increase in desirable plant species with a concomitant improvement
in range condition, and (4) research needs to be conducted to determine how these rangelands can be improved. 相似文献
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