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1.
Jean-Jacques Corre 《Landscape Ecology》1991,6(1-2):65-75
The Golfe du Lion is mainly bordered by low and narrow sand dunes. Since about four decades, 1/3 of its shoreline has been receding, while 1/3 has been prograding and another 1/3 is stable. Several types of dunes may be described mainly depending on storms, high wind frequencies and sand grain size. Vegetation on dune system is distributed along a primary gradient according to sand stability and soil development, and a secondary gradient along slope of dune according to a seasonal cycle of fresh and salt phreatic water level.Global changes in climate may influence these geomorphological and biological structures mainly through:- Winter minimum temperatures changing the distribution of several plant species, especially in the middle part of the Golfe du Lion.- Frequent high storms which cause damages to the front of the dune systems and disrupt the shore. Changes in dune ecosystems will be cyclic so these tendencies will be obvious only upon a long term period. 相似文献
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Extremely important to the climate in any region are the radiation balance and the exchange processes of heat, water vapour and momentum. Most climatological parameters (e.g. temperature, humidity, wind speed, cloudiness and precipitation) are the direct or indirect result of the radiation balance and these exchange processes.The weather of the West European coast from Tarifa (Spain) to Skagen (Denmark) is especially suitable for the formation of dunes. Often a wind is blowing, varying widely in force and direction. The conditions are optimal for the formation of high and wide dune complexes, given a large supply of sand by the sea. The annual precipitation surplus is considerable for most of this coast. This favours the establishment of vegetation, and thereby it enhances dune formation. The short distance to the land-sea border causes strong gradients in several climatological parameters. These gradients lead to mesoscale effects, such as land-sea breezes and coastal fronts. The varying vegetation cover and the presence of slopes in all directions induce a strongly varying microclimate. However, this microclimate is not unique to the coastal dunes. Unique is the interaction with the wide range of ambient weather, which is inherent to the coast.It is not possible to be conclusive about the effects of climatic change on coastal dunes because climate models are not yet able to predict the changes adequately and because these models supply information on the expected mean climate, but not on the actual weather. 相似文献
4.
Vegetation barriers have been widely applied along urban streets to improve roadside air quality. For a deep investigation of their influences, field measurements and numerical simulations are performed in this study. Carbon monoxide (CO) is selected as a representative of gaseous traffic emissions for both field observations and numerical models. Computational Fluid Dynamics (CFD) models of the standard k-ε turbulent model and Eulerian approach for species transport are solved by FLUENT solver. Results obtained from numerical simulations show a good agreement with field observations on the distribution of roadside CO. In perpendicular wind conditions, both field observations and numerical simulations present a prominent CO reduction over the slow lanes (footpath and bikeway) when vegetation barriers exist. To effectively mitigate roadside air pollution, numerical simulations also provide the optimal heights for roadside vegetation barriers in the given street canyons. For street canyons with an aspect ratio (the ratio of building height to street width) ranging from 0.3 to 1.67, 1.1 m can be used as an optimal height, and 2.0 m could serve as an alternative if tall vegetation barriers are considered. For street canyons with an aspect ratio of lower than 0.3, 0.9 m to 2.5 m can be considered as the optimal heights for roadside vegetation barriers. According to sensitivity analysis, the optimal heights for vegetation barriers are largely insensitive to wind velocities in the given street canyons. In the more complicated urban street canyons and complex meteorological conditions, the optimal heights can be determined by specific numerical simulations. These findings are expected to provide important insights into alleviation of gaseous mobile emissions in terms of vegetation barrier design in urban streets. 相似文献
5.
Existing spatial patterns of a forest are in part a product of its disturbance history. Using laser altimetry and field measures
of canopy top height to represent pre- and post-hurricane canopy topography, respectively, we measured changes in spatial
patterns of stand structure of a United States southern mixed coniferous-deciduous for est. Autocorrelative and fractal properties
were measured in this opportunistic study to quantify changes in canopy architecture along twelve, 190-250 m transects that
were subjected to moderate to high levels of wind disturbance. Prior to the hurricane, canopy heights were autocorrelated
at scales <40 m with an average fractal dimension of 1.71. After the disturbance, autocorrelation disappeared; the average
fractal dimension rose to 1.94. This shift towards spatial randomness illustrates part of the cyclical nature of ecosystem
development. It shows how a catastrophic collapse of biomass accumulation corresponds to a decrease in ecosystem organization
across a landscape.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
SummaryThe purpose of this study was to determine the relative importance of honeybee (Apis mellifera) activity and wind in the pollination of avocado (Persea americana Mill.) trees. Data on the pollination rates of five cultivars of avocado, honeybee densities, ambient temperatures, and wind velocities were recorded in an orchard in Israel on 61 d over a period of 7 years. The effect of wind velocity on avocado-flower pollen under laboratory conditions was also studied. Rates of pollination showed highly positive correlations with honeybee density, whereas no correlations were observed with wind velocity. Under laboratory conditions, no effect of wind velocities equivalent to those measured in the field was observed on avocado-flower pollen. Our results agree with earlier work in which wind contributed only slightly to avocado yield. Hence, we conclude that contrasting data which show the effectiveness of wind pollination in avocado are not relevant to most avocado-growing regions, including Israel and California. It is, therefore, strongly recommended that avocado growers continue using honeybees for pollination. 相似文献
7.
Physical influences of landscape on a large-extent ecological disturbance: the northeastern North American ice storm of 1998 总被引：3，自引：1，他引：3
The 1998 ice storm was a large-extent ecological disturbance that severely affected the eastern Adirondack forests of northern New York. Ice damage produced widespread breakage of limbs and trunks in susceptible trees. Although ice storms are common within northeastern North American forests, the magnitude and extent of the 1998 storm far exceeded damage caused by typical ice storms in the recent past. While plot and stand-scale ecological impacts of ice storms have received attention insofar as tree species vulnerability, stand age susceptibility, and microhabitat alterations, larger-extent damage patterns have not been previously evaluated. The normalized difference vegetation index (NDVI) was employed to assess forest vigor and canopy density in atmospherically corrected Landsat Thematic Mapper (TM) satellite imagery of the Adirondacks. Digital change analysis of the baseline forest condition (1990 NDVI data), and the condition encountered in a post-storm image (1998 NDVI data) was conducted. Forest damage was separated from natural variations in canopy reflectance by employing a generalized linear model that incorporated in situ measurements. A robust empirical variogram analysis revealed that locations of tree damage were significantly correlated for distances up to 300 meters. Intensely-damaged forest exhibited greater spatial dependence, but over a smaller distance. Canopy damage was not greater proximate to stream and forest boundaries, and did not follow our hypothesis of decreasing damage with distance from the boundary. Overall, we show that local topography (elevation and aspect), forest composition (deciduous or coniferous), and the meteorological characteristics of the disturbance event acted together to determine the spatial extent of ice storm damage.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
8.
Wind farms are positioned in open landscapes and may cause loss of wildlife habitat due to disturbance, fragmentation, and
infrastructure development. Especially flocking geese, swans, ducks and waders are regarded as vulnerable to wind farm development.
We compared past and current displacement effects of two onshore wind farms and a line of land-based turbines on spring-staging
pink-footed geese (Anser brachyrhynchus) to see if there was evidence of habituation. In one wind farm area, geese previously (1998) (Larsen and Madsen 2000) kept a distance of c. 200 m (the distance at which 50% of peak densities is reached) and they did not go between the turbines;
today (2008) they keep a distance of c. 100 m, but do still not enter the wind farm area. In another wind farm, where foraging
geese previously (2000) kept a distance of more than 100 m and did not enter the wind farm, they now (2008) forage between
the wind turbines and keep a distance of c. 40 m to turbines. In 1998, geese kept a distance of 125 m to a line of turbines,
compared to 50 m now. We conclude that geese have behaviorally adapted to changing landscapes created by wind farms. The difference
in avoidance between the sites may be due to the sizes of the turbines which in this study were small in both rotor-swept
area and in height compared to more recent “industry standard” of 2.5 and 3.0 MW turbines. The study points to the need for
longer term studies to properly assess the impact of wind farms on wildlife, including consequent increased risks from inclement
weather events of feeding, rafting, and migrating waterfowl. 相似文献
9.
The early studies about the plant ecology of Doñana carried out at a small scale showed that the main process controlling vegetation composition of the stabilized dunes was soil water availability. However, the extrapolation of this model to larger spatial scales failed to explain observed vegetation patterns. In this work, the vegetation patterns and the processes causing them are studied at a larger scale. Data of topography, soil pH, electrical conductivity, and available iron allowed to distinguish three large geomorphologic zones on the stabilized dunes of the Doñana Biological Reserve which correspond to different dune building episodes. Different dune episodes showed differences in both water table depth and dynamics, which are due to groundwater flow systems of different scale. It is further manifested by differences in shrub composition. The results show that geomorphology controls the vegetation pattern at different scales mediated through water availability. Differences in water availability are due to the connection to groundwater flow systems of contrasted scale. On a small scale (10−102 m), along dune slopes, there is a gradient from dune ridges to slacks, from xerophyte to hygrophyte vegetation types. On a mesoscale (102−103 m), there are several dune episodes with variable topographic altitude, dominated by different types of xerophytes. On a regional scale (>103 m), the discharges of the regional aquifer produce strong environmental and biotic stresses resulting in a mixed community. 相似文献
10.
This paper discusses the combined influence of building morphology and trees on air pollutant concentrations in the Marylebone neighbourhood (central London). Computational Fluid Dynamics (CFD) simulations are performed with OpenFOAM using the k-ε model. Aerodynamic and deposition effects of Platanus acerifolia trees are considered. While aerodynamic effects are treated as typically done in the literature, i.e. as a porous media, for the deposition an enhanced model with an additional sink term was implemented. CFD results are compared with UK AURN (Automatic Urban and Rural Network) station concentrations. Several meteorological conditions are analysed based on London City Airport weather station data, with attention to prevailing winds.CFD simulations show that trees trap air pollution by up to about 7% at the Marylebone monitoring station in the spring, autumn and summer seasons, suggesting that the aerodynamic effects are similar over the different leaf seasons. Aerodynamic effects are more important at lower wind speeds causing little turbulent dispersion. Deposition effects are found to be 4 times less important with reductions of up to about 2%, with more deposition in summer due to a greater leaf area density. Furthermore, for winds parallel to Marylebone Road, the aerodynamic effects decrease concentrations suggesting that in such cases trees could be considered as a mitigation measures. This is different from perpendicular winds for which trees exacerbate trapping, as found in previous studies. The analysis of concentration levels obtained from CFD simulations across the whole street confirms a beneficial aerodynamic dispersive effect of trees of 0.7% in summer time for all wind directions averaged at a wind speed of 5 m/s (yearly average wind speed observed in the area). Results highlight the need to account for both aerodynamic and dispersion effects of trees in CFD modelling to achieve a comprehensive evaluation and help city planners with a sustainable design of trees in urban environments. 相似文献
11.
Michel Riksen Rita Ketner-Oostra Chris van Turnhout Marijn Nijssen Dirk Goossens Pim D. Jungerius Wim Spaan 《Landscape Ecology》2006,21(3):431-447
In the Netherlands the total active inland drift-sand area has been declining rapidly during the last 50 years. To preserve
the inland drift sands, it is necessary to understand its origin and development and the role of human activity in this semi-natural
ecotype. The objective of this literature review is to describe the development of the drift-sand ecotopes, to explain the
rapid decline of the active drift sands, and to develop a management strategy for the remaining active drift sands. Inland
drift-sand landscapes are relatively young landscapes of Holocene age. They often occur as oval-shaped cells with a length
of 1.5 to over 6 km in the direction of the prevailing wind. These cells presumably represent reactivated deposits of Younger
Cover Sands. Large-scale erosion events in combination with human activity suppressed the development of vegetation. After
the change in land use in the first half of the 20th century in which most of the drift sands were re-afforested, the vegetation
succession started to show a progressive development. In this stage inland drift-sand ecotopes developed in most of the remaining
drift sands with all forms of the typical succession stages from bare sand to forest. The rate at which this development took
place mainly depended on the geomorphological development stage of the area, the area size and human activity. Since the 1960s
the increased nitrogen deposition has accelerated the vegetation succession, not only resulting in a further decline of the
drift sands, but also in a loss of the fragile balance between the different ecotopes and loss of its typical habitants like
the Tree Grayling and Tawny Pipit. Most drift-sand vegetation and fauna need the presence of bare sand nearby and a certain
level of erosion activity to survive. To preserve the drift-sand ecotype, it is therefore recommended to keep the area affected
by erosion sufficiently large (process management). In the meantime one should also ‘maintain’ or increase the wind force
in the drift-sand area by suppressing the growth of high vegetation and removing trees, which form a wind barrier. In areas
which are less suitable for reactivation, one could restore the mosaic vegetation by removing the vegetation on a limited
scale (pattern management). More research is needed to develop a more balanced management strategy and to develop a management
tool for the managers of inland drift sands. Also the role of the increased nitrogen deposition in the regeneration process
needs further investigation in order to find an effective way to suppress its effect. The development of management strategies
for the Dutch inland drift sands might be of great value to drift-sand areas in Western Europe where nature conservationists
start to show more interest in the restoration of former drift-sand areas. 相似文献
12.
13.
Near-future sea level impacts on coastal dune landscapes 总被引：1，自引：0，他引：1
R. W. G. Carter 《Landscape Ecology》1991,6(1-2):29-39
Very little attention has been paid to the impact of global warming, especially sea level rise, on coastal dunescapes, despite the fact that these provide natural protection along many of the world's shorelines. This paper reviews likely responses given the IPCC climate change predictions to 2030AD, which include sea level rise in the order of 0.09 to 0.29m. It is envisaged that coastal dunes will react in a variety of ways dependent both on regional and local factors. Rising water levels will increase susceptibility to erosion, but the fate of released sediment, particularly the onshore/offshore partitioning, must depend on morphodynamic antecedence, and the propensity for periodic domain shifts. The release of material at the shoreline may allow construction of coastal dunes, to the point of progradation in some zones. The response of dune vegetation to a warmer, wetter climate is uncertain. Most of the main temperate dune species are C3 plants which given favourable conditions would respond positively to CO2 enhancement. However local factors may offset such potential gains. 相似文献
14.
Increasing fertiliser use in agricultural landscapes is likely to threaten the viability of remnant native vegetation in many
parts of the world. Australia’s prime grain production landscapes have nutrient poor soils, which formerly supported semi-arid
woodland. The ecological function and capacity for regeneration of these remnants may be particularly susceptible to nutrient
enrichment. The key sources of nutrients are wind and water deposition from crop fertilisation, and manure and feed from sheep.
We hypothesised that these sources would result in unequal deposition of nutrients within and among remnant vegetation patches.
We surveyed soil nutrients (Total N, Available P and K, C:N ratio, and soil pH) in the edges and interiors of 60 remnant woodland
patches of various sizes, and in adjacent cultivated paddocks. Nutrient load was negatively correlated with remnant size and
patterns were particularly strong for available P. Small remnant patches (<3 ha) were accumulation zones for nutrients, with
levels comparable or higher than within crop lands. The patterns are consistent with the hypothesis that small remnants are
strongly enriched as a result of being used for livestock shelter. In larger remnants, the primary cause of enrichment is
consistent with edge accumulation of nutrients due to wind and water movement. In large patches, remnant edges, particularly
the windward edge, were elevated compared to interiors of large patches. In these semi-arid crop lands, current trends in
intensification of cropping and a shift away from livestock may reduce the input of nutrients to small patches but increase
the nutrient threat to larger remnants. 相似文献
15.
It has been shown that the spatial configuration of a green area can strongly influence its cooling effect. However, the specific correlation has not been sufficiently studied. To systematically clarify the correlation between the spatial configuration and the cooling effect of green areas, 25 idealized scenarios are designed and simulated using the microclimate model ENVI-met. These 25 scenarios represent green areas with five different spatial configurations (integrated green area, sparse dotted green areas, dense dotted green areas, belt-shaped green areas parallel to wind direction, and belt-shaped green areas vertical to wind direction) and five vegetation types (trees with big canopies, trees with small canopies, hedges and shrubs, 50 cm grass, and 10 cm grass). The human thermal comfort of each scenario is evaluated by means of physiologically equivalent temperature (PET) using Rayman. The results reveal the influence of the fragmentation degree (quantified by the patch density and edge density), shape complexity (quantified by the land shape index), orientation of green belt, and vegetation type on the cooling effect of a green area. The spatial configuration and the vegetation type of green areas were found jointly affecting the efficiency of the green areas’ cooling effect. The highest cooling effect appears at 2 pm, reaching 6.3 K in the scenario of belt-shaped green areas parallel to the wind direction and with big canopy trees. The conclusions of this paper can provide suggestions for the climate-adaptive design and planning of urban green areas in the future. 相似文献
16.
The Dutch coastline is expected to change considerably during the next 100 years. Erosion will prevail, although accretion will occur locally.To establish a new policy for coastal defence management an integrated policy analysis study was performed. Major dune functions (nature conservation, recreation, public drinking water supply, housing and industry) have been inventarized by using a Geographic Information System.This study reports on the part of the analysis which takes nature conservation interests into account. Evaluation of nature interests has been based on the criteria: rarity and diversity of plant species c.q. vegetation types, succession stage, and completeness. This results in a classification of nature into five classes, based on abiotic as well as biotic characteristics of the landscape. Losses of nature interests were studied due to: loss of land because of shoreline retreat, to remodelling of the foredune ridge, and to changes of the dune groundwater level.An evaluation is given of the methods used to assess ecological impacts.Ideas are presented for further research on the prediction of ecological impacts and on coastline management which combines traditional coastal defence with nature conservation. 相似文献
17.
The Saler Beach dune field in Spain was partially destroyed between 1970 and 1973 due to building development. Presently great efforts to restore some dunes has begun. The possible consequence of a sea level rise for the Saler dune field is discussed according to different scenarios. 相似文献
18.
To test the effects of connectivity on fish diversity in isolated reef patches we deployed pairs of artificial reefs (AR)
at constant distances (12 and 25 m) from a large continuous reef and added series of small ARs to half of them. These small
reefs served as stepping-stones to increase fish movement between the large ARs and the continuous reef. Species gain and
loss curves were compared to obtain deeper understanding of the underlying mechanisms in relation to the theory of island
biogeography. We found that AR without stepping-stones maintained up to 57-fold more individuals than ARs with stepping-stones
during mass recruitment events that were dominated by the family Apogonidae. However, in-between these mass recruitment events
the overall impact of the stepping-stones on richness and abundance was small. By contrast, increasing distance from the continuous
reef from 12 to 25 m increased fish richness, although this was confounded with time since AR deployment. Increase in richness
with distance was predominantly caused by elevated species gain. Our results suggest that fish assemblages respond in distinct
ways to two types of isolation: (1) Increased richness with distance from a continuous reef, and (2) increased fluctuation
in abundance with decreased connectivity. The latter may be the outcome of accumulation and then abrupt emigrations of fishes
from isolated reefs. This study confirms that the spatial setting of reef patches in relation to larger or continuous reefs
alters fish assemblages, which may be important for planning AR deployments that maximizes diversity. 相似文献
19.
SUMMARYInsecticide drift from an air assisted sprayer was measured on two occasions in an orchard in Cambridgeshire. Bioassays with two day old larvae of Pieris brassicae (cabbage white butterfly) showed similar effects from Cypermethrin and carbaryl (used as a fruit thinner). Both compounds gave 50% larval mortality at 20-25 m and 10% mortality at about 50 m. The effects of wind speed and shelter are considered, and the results are discussed in relation to the effects of drift from tractor-drawn hydraulic sprayers. 相似文献
20.
Annette C. Richardson Eric F. Walton John S. Meekings Helen L. Boldingh 《Scientia Horticulturae》2010
Carbohydrates were measured in axillary bud meristems from kiwifruit (Actinidia deliciosa (A.Chev.) C.F. Liang et A.R. Ferguson cultivar Hayward) to determine whether concentrations changed during winter dormancy. Buds were collected from kiwifruit vines growing in four sites, which spanned the climatic range that kiwifruit are grown in New Zealand, and from vines where the time of budbreak had been manipulated using hydrogen cyanamide. During winter, sugars comprised 78% of measured carbohydrates in meristems, with sucrose accounting for more than 86% of sugars detected (up to 200 mg g DW−1). Starch concentrations in bud meristems showed little change during winter. Meristem sucrose and hexose concentrations increased rapidly from autumn until mid-winter, and this was correlated with leaf abscission. Sugar accumulation ceased in mid-winter and concentrations remained stable until spring, suggesting that bud meristem activity was low. Four weeks before visible bud movement, a marked decline in sucrose and increase in hexose concentrations, indicated activity in the meristems had increased prior to budbreak. The patterns of seasonal change and peak sucrose concentrations in meristems were similar at all sites. The only difference was in the timing of events, with changes in meristem sugars occurring earliest in vines growing at the coolest site, coinciding with their earlier cessation of and resumption of vine growth. Advancing budbreak, by applying hydrogen cyanamide to vines in late winter, also advanced changes in sugar concentrations within meristems. This work suggests that the concentration of sucrose in kiwifruit bud meristems has utility as an indicator of whether they are being induced into, maintained or released from winter dormancy. 相似文献