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21.
Combating desertification in Iran over the last 50 years: An overview of changing approaches 总被引:1,自引:0,他引:1
Desertification in Iran was recognized between the 1930s and 1960s. This paper traces Iran’s attempts to reclaim desertified areas, evaluates the anti-desertification approaches adopted, and identifies continuing challenges. Iran has areas vulnerable to desertification due to extensive areas of drylands and increasing population pressure on land and water resources. Over-grazing of rangelands is a particular problem. Initially desertification was combated mainly at the local level and involved dune stabilization measures, especially the use of oil mulch, re-vegetation and windbreaks. Insufficient technical planning in the early years has led to changed approaches to plant densities and species diversity in plantations, and increased on-going management of existing plantations. Since the late 1980s forage and crop production has increased in areas where runoff control techniques are practiced. The social and economic aspects of anti-desertification programs have assisted in poverty reduction by providing off-season employment in rural areas. In 2004 a national plan to combat desertification was ratified and this placed an emphasis on community participation. Continuing challenges include managing existing desertified areas as well as taking into account potential future problems associated with rapidly depleting groundwater supplies and a predicted reduction in the plant growth period accompanying climate change. 相似文献
22.
The Countryside Council for Wales (CCW) is developing a management framework with the primary aim of restoring favourable
conservation status to the sand dune resource of Wales. It will take onboard the requirements of both national and international
conservation legislation and will also help CCW integrate its responsibilities for biodiversity, geodiversity, landscape,
access and recreation for this habitat. In order to achieve certain conservation goals it will be necessary to have in place
a variety of different types of management ranging from non- or minimal intervention through to intensive single species management
and habitat re-creation. However, it will not provide a comprehensive framework for all aspects of site management, but only
those that are deemed to be of strategic importance, and have significance within an all-Wales perspective for their nature
conservation importance. 相似文献
23.
Ammophila arenaria (marram or European beach grass) for dune stabilization in South Africa in the past and present, its present distribution
in South Africa, and the perceptions of coastal management agencies and the public about its further use. The planting of
A. arenaria became the most important means of dune stabilization, by human intervention, along the South African Cape coast in this
century. Its modern distribution from the semiarid west coast to the subtropical shores of the Eastern Cape extends through
various climatic zones. Although historical data are missing for some areas, there is no indication of its unaided spread.
A. arenaria occurs at most sites because of its prior planting. The South African climate appears to affect its vigor. However, concern
about the use of the alien grass has been raised since it has proved to be a highly invasive species in other parts of the
world, particularly along the North American west coast and in Tasmania. While the CSIR (Council of Scientific and Industrial
Research) promotes its use, CNC (Cape Nature Conservation) follows a policy that restricts the use of any alien plant, including
A. arenaria, and requests further research on its invasive properties. Although a questionnaire survey shows that stabilization sites
featuring large areas of A. arenaria are accepted by the South African public, current coastal management practices need to be analyzed critically. A thorough
investigation of the potential invasiveness of A. arenaria on South African coastal dunes will be essential and shed new light on the American A. arenaria problem. 相似文献
24.
D. van der Laan O. F. R. van Tongeren W. H. van der Putten G. Veenbaas 《Journal of Coastal Conservation》1997,3(2):179-190
In coastal foredunes marram grass (Ammophila arenaria) is used to stabilize windblown sand. The development of traditionally plantedAmmophila into a more natural foredune vegetation may take 5 – 10 yr. For economic reasons, traditional planting may be replaced by
alternative techniques such as planting seeds or disk-harrowing rhizome fragments. In this paper, we compare the initial vegetation
development of traditionally planted stands with stands established from seeds and from rhizomes.
The experiments were conducted on an artificial foredune originating from dredged sea sand. The total experimental area covered
more than 100 ha and the vegetation development was studied for 6 yr. The data were analysed bya priori grouping of plant species according to their ecology, as well as by Principal Components Analysis (PCA) and Redundancy Analysis
(RA) of the percentage ground cover per plant species.
Comparing ecological groups of plants showed that all planting methods delivered equal numbers of plant species that are indicative
for coastal dunes. PCA and RA showed that methods based on the use of rhizome material resulted in a higher percentage cover
of clonal perennials (Calammophila baltica, Festuca rubra ssp.arenaria, Carex arenaria andCirsium arvense) than the traditionally planted stands and the stands obtained from seeds. The latter two were characterized by the dominance
of annuals, bi-annuals and (mostly nonrhizomatous) perennials.
Initially, the rates of succession were highest in the stands obtained from rhizomes. However, after 3 – 6 yr there were no
differences between the various stands. During the first four years, the percentage cover by rhizomatous foredune plants developed
faster than that of annuals, bi-annuals and perennials. After 6 yr, the latter contributed almost as much to the percentage
cover as the clonal species.
Nomenclature: van der Meijden et al. (1990) for plant species. The plant species were classified into ecological groups according to van
der Meijden et al. (1991) and Mennema et al. (1980). 相似文献
25.
The effects of off-road vehicles (ORVs) on the dune system of Fire Island National Seashore, New York, USA, were examined through a detailed, two-year field study. The experimental approach was adopted in order to evaluate the environmental effects of ORVs in this zone. Adjacent control and impact sites were established in two locations. Vehicle impacts were applied at the equivalent rate of one vehicle pass per week. Monitoring of foredune vegetation through sequential quadrat surveys and construction of sea-ward limit maps showed a significant loss of vegetation resulting from ORV impacting. Loss of vegetation resulted in an alteration of the natural foredune profile, which could increase dune erosion during storm wave attack. 相似文献
26.
Column experiments to study nonlinear removal of bacteriophages by passage through saturated dune sand 总被引:1,自引:0,他引:1
In a recent field study on dune recharge, bacteriophages MS2 and PRD1 were found to be removed 3 log10 over the first 2.4 m and only 5 log10 over the next 27 m. To understand the causes of this nonlinear removal, column experiments were carried out under conditions similar to the field: same recharge water, temperature (5 +/- 3 degrees C) and pore water velocity (1.5 m day(-1)). Soil samples were taken along a streamline between the recharge canal and the first monitoring well. Bacteriophage phiX174 was included for comparison. The high initial removal in the field was found not to be due to heterogeneity of phage suspensions but to soil heterogeneity. Phage removal rates correlated strongly positively with soil organic carbon content, and relatively strongly positively with silt content and the presence of ferric oxyhydroxides. Soil organic carbon content, silt content and the presence of ferric oxyhydroxides were found to decrease exponentially with travel distance. Removal rates of phiX174 were found to be 3-10 times higher than those of MS2 and PRD1 due to the lower electrostatic repulsion that the less negatively charged phiX174 experiences. It is suggested that the high initial removal in the field is due to the presence of favorable sites for attachment formed by ferric oxyhydroxides that decrease exponentially with travel distance. Similar removal rates may be found at both laboratory and field scale. However, due to local variations at field scale detailed knowledge on soil heterogeneity may be needed to enable a reliable prediction of removal. 相似文献
27.
The impact of grazing on spider communities in a mesophytic calcareous dune grassland 总被引:1,自引:0,他引:1
During 1994–1995 and 1997–1998 spiders were sampled with pitfall traps in a botanically rich, mesophytic, calcareous dune
grassland in Belgium. As a consequence of intensive cattle grazing, vegetation variation in a large part of the area had diminished.
The study area was also patchily grazed by rabbits. Community analysis with TWINSPAN revealed five distinct spider communities.
Ecological differentiation was best explained by combination of the habitat variables: distance from grazed or non-grazed
vegetation,Rosa pimpinellifolia cover and grass cover in both summer and winter. Species diversity was highest in the border zone between the cattle-grazed
and non cattle-grazed sites.
Correlation of the most abundant spider species with the vegetation determinants explains the ecological differentiation between
the spider communities. Species were classified into seven major groups that reflect the species’ habitat preferences. The
group showing clear association with non cattle-grazed, tall vegetation consists of common species. Characteristic species
for the intensively cattle-grazed sites are common aeronauts and rare species such asWalckenaeria stylifrons, Mastigusa arietina, Ceratinopsis romana andPardosa monticola. The latter are shown to be dependent on ungrazed vegetation for juvenile development and overwintering. Intensive grazing
results in homogeneous short vegetation, which can only be colonized by ‘open ground’ species with a well-developed dispersal
capacity, or by species which are not dependent on litter-rich situations for juvenile development. An extensive cattle grazing
regime results in a patchy mosaic grassland where, in addition to the above mentioned groups of species, other species survive
by migrating between the buffered litter rich ungrazed vegetation and the short vegetation. Additionally, some typical and
rare species prefer the transition zone between the grazed and the ungrazed vegetation because they are associated with specific
habitat structures or inhabiting ant-species. 相似文献
28.
During 1994–1995 and 1997–1998 spiders were sampled with pitfall traps in a botanically rich, mesophytic, calcareous dune
grassland in Belgium. As a consequence of intensive cattle grazing, vegetation variation in a large part of the area had diminished.
The study area was also patchily grazed by rabbits. Community analysis with TWINSPAN revealed five distinct spider communities.
Ecological differentiation was best explained by combination of the habitat variables: distance from grazed or non-grazed
vegetation,Rosa pimpinellifolia cover and grass cover in both summer and winter. Species diversity was highest in the border zone between the cattle-grazed
and non cattle-grazed sites.
Correlation of the most abundant spider species with the vegetation determinants explains the ecological differentiation between
the spider communities. Species were classified into seven major groups that reflect the species’ habitat preferences. The
group showing clear association with non cattle-grazed, tall vegetation consists of common species. Characteristic species
for the intensively cattle-grazed sites are common aeronauts and rare species such asWalckenaeria stylifrons, Mastigusa arietina, Ceratinopsis romana andPardosa monticola. The latter are shown to be dependent on ungrazed vegetation for juvenile development and overwintering. Intensive grazing
results in homogeneous short vegetation, which can only be colonized by ‘open ground’ species with a well-developed dispersal
capacity, or by species which are not dependent on litter-rich situations for juvenile development. An extensive cattle grazing
regime results in a patchy mosaic grassland where, in addition to the above mentioned groups of species, other species survive
by migrating between the buffered litter rich ungrazed vegetation and the short vegetation. Additionally, some typical and
rare species prefer the transition zone between the grazed and the ungrazed vegetation because they are associated with specific
habitat structures or inhabiting ant-species.
Nomenclature: Roberts (1987, 1995) forAraneae; van der Meijden et al. (1990) for vascular plants; Corly et al. (1981) for bryophytes; Schaminée et al. (1996) for vegetation
associations. 相似文献
29.
Ritchie William 《Journal of Coastal Conservation》2000,6(1):207-218
The Sands of Forvie, National Nature Reserve, Scotland is a complex coastal sand dune system which is associated with the
dynamic estuary of the River Ythan. The dune system has developed over more than 5000 years. The south partis a peninsula
of dunes, sandhills, sand arcs, erosion and deflation surfaces. The north part is superimposed on a rock plateau with a cliff
coastline. This plateau is covered in glacial deposits and is essentially an upland heath landscape. Some of the best examples
of large active parabolic dunes in Britain are found in North Forvie. The sequence of geomorphic development is described.
As a nature reserve with a rich ecology it has been managed for conservational purposes since 1960s. As such it is an excellent
case study of how conservational management has changed to become more flexible and more aware of the importance of dynamic
processes. 相似文献
30.
Joost H. M. de Ruig 《Journal of Coastal Conservation》1998,4(2):127-134
The boundary between land and sea in The Netherlands changes continuously. Every kilometre of the present position of the
Dutch sandy coastline is the result of the interface between natural dynamics initiated by the sea and man-made action on
land.
Before 1990, each year ca. 20 ha of dunes disappeared through coastal retreat. In 1990 the Dutch government decided to stop
any further long-term coastal recession and chose for ‘dynamic preservation’, which primarily aims, at ensuring safety against
flooding and sustainable preservation of the values and interests attached to the dunes and beaches.
Five years later, a first review of the benefits and bottlenecks of the new coastal defence policy could be presented. The
overall conclusion is that the 1990-choice for dynamic preservation was right. The considerable losses of dunes and beaches
do not occur any longer. Sand nourishment is an effective method of coastline maintenance, which also serves the functions
of the beach and dune area for human society.
However, serious erosion of the deeper part of the shoreface threatens the coastline of the 21st century. Nearly a doubling
of the nourishment volume is necessary to prevent a renewed landward shift of the coastline. An anticipated accelerated sea
level rise (ca. 60 cm/century) will increase the sand losses by another 25%.
Plans are being finalized for large-scale land reclamation in front of the coastline as an answer to growing spatial problems
on land. In other plans polders, now safely protected by sea dikes, will be returned to the sea in order to restore ecologically
valuable salt marshes and mud flats.
The position of the coastline will continue to change in the coming decades. Besides natural dynamics, human use of the coastal
zone will certainly affect this process: measures to maintain the coastline at its 1990 position need to be seen in perspective:
the coastline as a part of the coastalzone. 相似文献