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1.
The machair sand dune systems of the Outer Hebrides of Scotland are a unique habitat, which is rare within both a global and
European context. Unusually, the machair habitat also represents an agricultural resource that is very important to the Hebridean
people, having been subject to both grazing and cultivation throughout the historical period. Following designation as an
Environmentally Sensitive Area (ESA) in 1988, the machairs of South Uist have been studied with the aim of understanding the
links between agricultural practice and their plant community and ecosystem dynamics. This research focused primarily on the
effects of cultivation practices and their role in maintaining plant species richness and community and ecosystem stability.
Within two carefully selected areas, the successional plant communities of machair at different stages of recovery following
ploughing and cultivation of cereals and potato patches or ‘lazy beds’ were identified at both a macro- and micro-level. Investigations
of the vegetation recovery processes on turves taken from newly ploughed land indicated that the initial stages of recolonization
are characterized primarily by rapid vegetative reproduction and growth, although re-vegetation by seeds is also an important
factor. The implications of these findings for the long-term management of machair plant communities are discussed and in
particular the need to maintain old cultivation practices such as shallow ploughing. The need for more detailed research into
both seed banks and seed rain and into processes of vegetative reproduction is stressed.
Nomenclature: Clapham et al. (1981) and Stace (1991, 1997) for vascular plants; Hubbard (1984) for grasses; Pankhurst & Mullin (1991) for
the regional flora; Dobson (1992) for lichens; Watson (1981) for mosses and liverworts. 相似文献
2.
Jerry F. Franklin 《Environmental management》1979,3(1):2-5
Simulation models are becoming increasingly important as tools for synthesizing and applying information in almost all aspects of land management. They are particulary valuable for predicting and comparing outcomes of alternative decisions and assumptions. Models also permit managers to consider and integrate the potential influences of a large number of variables. 相似文献
3.
The origin of the grassy balds of the Great Smoky Mountains is examined. Some of the areas were cleared by settlers. Grazing by sheep and cattle and the cutting of trees were probably the most important factors in maintaining the grass sward; fire apparently was not used.Vegetation survey plots indicated that little of the original balds' area was still grassy and that most of the invading trees and shrubs could be expected to sprout if cut or burned. Areas presently trampled or mowed had a flora similar to a bald that was still grazed. High-elevation burn scars had many species in common with the grassy balds but had dissimilar community structures; therefore, a policy favoring natural fires would be unlikely to encourage maintanence or formation of grassy balds.The management of open grassy areas on National Forest lands was investigated. Burning was the favored technique, although hand cutting, mowing, and grazing were used. The results of testing various management practices on Gregory Bald are reviewed in terms of cost, impact, and historical authenticity. Implications for park management are discussed. 相似文献
4.
根据我们对南岳广济寺森林群落的实地考察及其调查资料统计分析结果,发现该群落是一种尚未报道的新类型,即水丝梨+甜槠-尾叶山茶+花竹-蔓赤 车群丛(Association of Sycopsis sinensis+Castnopsis eyeri-Camellia caudata+Phyllostachys nidularia-Pellionia scabra)。该群落内有维管束植物69科116属149种;其属的区系是以热带性质成分为主,温带性质成分为辅,各占56.19%和43.81%;其种的区系成分以华夏、东亚、中国-日本和华东至华中等四种类型为主,同时本群落具有明显的华东至华中过渡交迭性质。在群落中木本植物和草本植物各占71.14%和28.86%,草本植物中的多年生和一年生类型各占22.82%和6.04%。本群落可以明显划分为乔、灌、草三个层次,每个层次又可以进一步划分为三个亚层。这一群落是中亚热带东部典型常绿阔叶林北部植被地理亚带中的常绿阔叶林,在演替过程中,群落仍将保持以水丝梨为优势种的常绿阔叶林,但其亚优势种——甜槠将可能会被多脉青冈、中华石楠、长叶石栎取代。 相似文献
5.
M. A. C. Veer 《Journal of Coastal Conservation》1997,3(1):41-48
The encroachment of some tall grass species in open dune vegetation, as observed in a Dutch dry dune area, is considered unfavourable
from a conservation viewpoint. This paper investigates differences in vegetation and soil properties between grass-dominated
and still existing open dune grassland plots at four locations along the coast. Soil properties studied include nitrogen and
phosphorus pools and nitrogen availability by mineralization. Vegetation properties included are above and below-ground biomass
and nitrogen and phosphorus concentrations in above-ground biomass.
Systematic differences in N-pools between grass-dominated and open dune grassland plots were not observed. However, N-availability
by mineralization and its turnover rates are higher in grass-dominated plots than in open dune grassland plots, as well as
above and below-ground biomass. In open dune grassland plots, atmospheric N-input is an important source of N, whereas in
grass-dominated plots mineralization largely exceeds atmospheric N-input. However, these observations do not explain the mosaic-like
vegetation pattern. Grazing intensity is most likely the determinant factor in the dry dune system. It is concluded, that
grass encroachment is probably triggered by atmospheric deposition and is enhanced by positive feedbacks in the N-cycle. The
relevance of these results for restoration management is briefly discussed. 相似文献
6.
A. J. van der Graaf D. Bos M. J. J. E. Loonen M. Engelmoer R. H. Drent 《Journal of Coastal Conservation》2002,8(2):179-188
We studied the impact of livestock grazing on the distribution ofBranta bernicla bernicla (Dark-bellied Brent goose) in the Dutch Wadden Sea during spring. It was hypothesized that livestock facilitate short-term
(within-season) grazing for geese as well as long-term (over years). Therefore we measured grazing pressure by geese in salt
marsh and polder areas that were either grazed (spring-grazed) or ungrazed during spring (summer-grazed). Additionally, we
carried out a preference experiment with captive geese to test the preference between spring-grazed and summer-grazed polder
swards. We furthermore compared patterns of use by geese between long-term ungrazed and grazed salt marshes.
In May, there is a difference in grazing pressure by geese between polder pastures that are grazed or ungrazed during spring.
In this month, the ungrazed polder pastures are abandoned and the geese shift to either the grazed polder pastures or to the
salt marsh. Vegetation in the polder that had been spring-grazed had a lower canopy height and a higher tiller density than
summer-grazed vegetation. The captive geese in the preference experiment showed a clear preference for vegetation that had
been spring-grazed by sheep over ungrazed vegetation. Goose grazing pressure was negatively correlated to canopy height, both
on the polder and on the salt marsh. Within the plant communities dominated byFestuca rubra andPuccinellia maritima, marshes that were intensively grazed by livestock generally had higher grazing pressure by geese than long-term ungrazed
or lightly grazed salt marshes. 相似文献
7.
The systematic conservation planning literature invariably assumes that the biodiversity features being preserved in sites do not change through time. We develop a conservation planning framework for ecosystems where disturbance events and succession drive vegetation dynamics. The framework incorporates three key attributes of disturbance theory: heterogeneity in disturbance rates, spatial correlation between disturbance events and different impacts of disturbance. In our conservation problem we wish to maximise the chance that we represent a certain number of successional types given a cap on the number of sites we can conserve. Correlation between disturbance events dramatically complicates the problem of choosing the optimal suite of sites. However, in our problem we discover that spatial correlation in disturbances affects the optimal reserve network very little. The reason is twofold: (i) through our probabilistic framework we focus on the long-term effectiveness of reserve networks and (ii) in the dynamics considered in our model the state of a site is not only affected by the most recent (correlated) disturbance event but also by the site's long-term stochastic history which blurs the impact of spatial correlation. If successional states are the conservation target rather than individual species then, conserving a site can only contribute to meeting one target. However, given that correlation of disturbance events may be ignored, we show that if the number of candidate reserves is sufficiently large the statistical dependence of different conservation targets may be ignored, too. We conclude that the computational complexity of reserve selection methods for dynamic ecosystems can be much simpler than they first appear. 相似文献
8.
Salt marsh development on the coastal barrier island of Schiermonnikoog (The Netherlands) was compared with two other salt
marsh systems in the Wadden Sea. Accretion rate, nitrogen accumulation and changes in plant species composition were investigated
using chronosequences. The age of the marsh was estimated from aerial photographs and old maps. In 7230 plots, the elevation
of the marsh surface, the thickness of the sediment layer (clay) and the presence of plant species was recorded. In addition,
the nitrogen pool was measured at each successional stage.
Accretion rates were similar in the three salt marshes. Higher accretion rates were found at younger marshes. A strong linear
relationship between nitrogen pool size and thickness of the clay layer was found for the three marshes. The accumulation
rate of nitrogen is therefore strongly related to the accretion rate. Thus, more nitrogen is present in the sediment of later
successional stages where more clay has accumulated. On the high salt marsh (55 cm+MHT),Ameria maritima disappeared andArtemisia maritima, Juncus gerardi andElymus athericus established at sites with a thicker clay layer. On the low salt marsh (25 cm+MHT),Plantago maritima, Puccinellia maritima andLimonium vulgare disappeared andAtriplex (Halimione) portulacoides established. Apparently, with the accumulation of clay and therefore of nitrogen, tall growing species take over in salt
marshes not grazed by livestock. 相似文献
9.
A review of results of fertilization experiments in wet dune slacks is presented. In most cases the above-ground biomass appeared
to be limited by nitrogen availability. Primary phosphorus limitation was assessed only once in a dune slack where sod cutting
had been applied very recently. In most other case studies phosphorus limits biomass production after nitrogen deficiency
was lifted. Potassium availability is of minor importance for biomass production in this type of ecosystem. Singular nitrogen
additions led to increased dominance ofCarex andJuncus species as well as perennial grasses, such asAgrostis stolonifera andCalamagrostis epigejos. A combined addition of nitrogen and phosphorus led to total dominance of grasses, while the characteristic basiphilous pioneer
species (including mosses) decreased or even disappeared. Certain mechanisms are considered which may maintain nutrient availability
in slacks with basiphilous pioneer vegetation at a low level, despite of the accumulation of nutrients in the developing organic
soil layer. Some implications for management and further research are discussed. 相似文献
10.
Management of ecological reserve lands should rely on the best available science to achieve the goal of biodiversity conservation.
“Adaptive Resource Management” is the current template to ensure that management decisions are reasoned and that decisions
increase understanding of the system being managed. In systems with little human disturbance, certain management decisions
are clear; steps to protect native species usually include the removal of invasive species. In highly modified systems, however,
appropriate management steps to conserve biodiversity are not as readily evident. Managers must, more than ever, rely upon
the development and testing of hypotheses to make rational management decisions. We present a case study of modern reserve
management wherein beavers (Castor canadensis) were suspected of destroying habitat for endangered songbirds (least Bell’s vireo, Vireo bellii pusillus, and southwestern willow flycatcher, Empidonax traillii extimus) and for promoting the invasion of an exotic plant (tamarisk, Tamarix spp.) at an artificial reservoir in southern California. This case study documents the consequences of failing to follow
the process of Adaptive Resource Management. Managers made decisions that were unsupported by the scientific literature, and
actions taken were likely counterproductive. The opportunity to increase knowledge of the ecosystem was lost. Uninformed management
decisions, essentially “management by assertion,” undermine the long-term prospects for biodiversity conservation. 相似文献