排序方式: 共有2条查询结果,搜索用时 46 毫秒
1
1.
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
2.
F. P. Sival A. P. Grootjans P. J. Stuyfzand T. Verschoore de la Houssaye 《Journal of Coastal Conservation》1997,3(1):79-86
Basiphilous, open, species-rich vegetation types of young dune slacks have declined throughout Europe in recent years, and
have largely been replaced by often acidophilous, tall marsh and scrub vegetation. This succession appears to be accelerated
by a decrease in the discharge of calcareous groundwater from sandy ridges or small dune hummocks. The present study deals
with spatial and temporal variation in the chemical composition of the groundwater in the upper metres of the soil of a degraded
dune slack complex on the Dutch barrier island of Schiermonnikoog, with emphasis on (1) groundwater composition, (2) water
level and (3) decalcification patterns. The main aim was to assess perspectives for restoring basiphilous vegetation types
which had been abundant in this slack from 1954 to 1977. The depth of decalcification was related to former hydrological conditions
along a transect of 200 m. Acidifying effects of rainfall were reflected in the chemical composition of the groundwater below
small dune hummocks within the slack. Distinct precipitation water lenses, poor in dissolved ions, were formed under the dune
hummocks during a wet period. This microtopography did not contribute to the discharge of calcareous groundwater to lowlying
parts of the slack. Here, groundwater showed decreasing concentrations of the dissolved ions after a rain shower. Except for
the peripheral sections of the slack—where upward seepage of groundwater (exfiltration)still occurs—infiltration conditions
are now dominant in the slack. The consequences of the present hydrological conditions for restoration are briefly discussed. 相似文献
1