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1.
Jian Yang Thomas E. Dilts Lea A. Condon P. Lee Turner Peter J. Weisberg 《Landscape Ecology》2011,26(3):381-395
Riparian vegetation is distinct from adjacent upland terrestrial vegetation and its distribution is affected by various environmental
controls operating at the longitudinal scale (along the river) or transverse scale (perpendicular to the river). Although
several studies have shown how the relative importance of transverse or longitudinal influences varies with the scale of observation,
few have examined how the influences of the two scales vary with the level of ecological organization. We modeled vegetation-environment
relationships at three hierarchically nested levels of ecological organization: species, plant community, and vegetation type.
Our hierarchically structured analyses differentiated the spatial extent of riparian zones from adjacent upland vegetation,
the distribution of plant community types within the riparian zone, and the distribution of plant species within community
types. Longitudinal gradients associated with climate and elevation exerted stronger effects at the species level than at
the community level. Transverse gradients related to lateral surface water flux and groundwater availability distinguished
riparian and upland vegetation types, although longitudinal gradients of variation better predicted species composition within
either riparian or upland communities. We concur with other studies of riparian landscape ecology that the relative predictive
power of environmental controls for modeling patterns of biodiversity is confounded with the spatial extent of the study area
and sampling scheme. A hierarchical approach to spatial modeling of vegetation-environment relationships will yield substantial
insights on riparian landscape patterns. 相似文献
2.
3.
To determine how vegetation pattern in early successional forests may be related to plant traits and types of disturbance,
we measured percent cover of individual taxa annually in a South Carolina Pinus elliottii forest, starting one year before, and ending four years after harvest and tree girdling disturbances were applied. The 17
most important taxa surveyed were grouped into four regeneration strategies chosen a priori, and the spatial patterns of these
groups and of the soil were investigated using global variability, semivariograms and kriged maps. We also examined spatial
correlations across years, across taxa, and between species and soil disturbance. Seed bank taxa represented by Dichanthelium spp. increased rapidly and formed large patches, and then quickly declined. Taxa that regenerate by newly dispersed seeds,
represented by Rhus copallina and Rubus spp. occurred at first in a few patches, and became widespread later. Stump sprouters, represented by Quercus spp. and Myrica cerifera, had rapid increases in cover, but their spatial patterns were largely determined by their pre-disturbance patterns. Prunus serotina, which relies on both sprouting and dispersed seed, had moderate cover and a random distribution. Within-species temporal
correlation of spatial pattern was lower in girdled than in harvested plots, and was not clearly related to regeneration strategy.
Forest floor disturbance was patchy and affected the pattern of Dichanthelium spp. in the harvested plots. Negative correlations between herbs and woody plants in harvested plots reflected the role of
biotic (i.e., successional) filters on vegetation pattern. Surprisingly, no spatial correlations were detected between the
nitrogen fixer, Myrica cerifera and other taxa in this N-limited system. In comparing the spatial and temporal patterns, we found kriged maps more informative
than analysis of semivariograms alone. The maps and correlation statistics demonstrated that regeneration traits, spatial
patterns of soil disturbances, and interactions among taxa influence dynamics of the spatial patterns of the plants. We also
demonstrated that disturbance types affected the importance and interactions among these three factors, and caused different
spatial patterns of the plant taxa. 相似文献
4.
Nicholas J. Berry Oliver L. Phillips Robert C. Ong Keith C. Hamer 《Landscape Ecology》2008,23(8):915-929
Selective logging of tropical forests imposes spatial pattern on the landscape by creating a mosaic of patches affected by
different intensities of disturbance. To understand the ecological impacts of selective logging it is therefore necessary
to explore how patterns of tree species composition are affected by this patchy disturbance. This study examines the impacts
of selective logging on species composition and spatial patterns of vegetation structure and tree diversity in Sabah, Borneo.
We compare tree diversity between logged and unlogged forest at three scales: species richness within plots, species turnover
among plots, and total species richness and composition of plots combined. Logging had no effect on tree diversity measured
at the smallest scale. Logged forest had a greater rate of species turnover with distance, so at a large spatial scale it
supported more tree species than the relatively homogeneous unlogged area. Tree species composition also differed significantly
between the two types of forest, with more small dipterocarps and large pioneers in logged forest, and more large dipterocarps
in unlogged forest. Our results emphasize the importance of sampling at a sufficiently large scale to represent patterns of
biodiversity within tropical forest landscapes. Large areas of production forest in SE Asia are threatened with conversion
to commercial crops; our findings show that selectively logged forest can retain considerable conservation value. 相似文献
5.
Disturbed habitats are often swiftly colonized by alien plant species. Human inhabited areas may act as sources from which
such aliens disperse, while road verges have been suggested as corridors facilitating their dispersal. We therefore hypothesized
that (i) houses and urban areas are propagule sources from which aliens disperse, and that (ii) road verges act as corridors
for their dispersal. We sampled presence and cover of aliens in 20 plots (6 × 25 m) per road at 5-km intervals for four roads,
nested within three localities around cities (n = 240). Plots consisted of three adjacent nested transects. Houses (n = 3,349) were mapped within a 5-km radius from plots using topographical maps. Environmental processes as predictors of alien
composition differed across spatial levels. At the broadest scale road-surface type, soil type, and competition from indigenous
plants were the strongest predictors of alien composition. Within localities disturbance-related variables such as distance
from dwellings and urban areas were associated with alien composition, but their effect differed between localities. Within
roads, density and proximity of houses was related to higher alien species richness. Plot distance from urban areas, however,
was not a significant predictor of alien richness or cover at any of the spatial levels, refuting the corridor hypothesis.
Verges hosted but did not facilitate the spread of alien species. The scale dependence and multiplicity of mechanisms explaining
alien plant communities found here highlight the importance of considering regional climatic gradients, landscape context
and road-verge properties themselves when managing verges.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
6.
Context
Ecological processes that shape diversity and spatial pattern of ecological communities are often altered by disturbance. Spatial patterns (spatial autocorrelation) in species diversity are thus expected to change with disturbance.Objective
When examining spatial patterns, ecologists traditionally lump positive and negative spatial autocorrelation into the overall spatial autocorrelation. By contrast, here we aim to understand disturbance effects on both positive and negative spatial autocorrelation of species richness and evenness, which may be related to environmental filtering and restricted dispersal, and to competition, respectively.Methods
For 8 years, we monitored the spatial autocorrelation in species richness and evenness of riparian plant communities in both uncut control and experimentally clearcut sites in the boreal forest of Alberta, Canada. The overall spatial autocorrelation for each of these two indices of diversity was separately decomposed into the components of positive and negative spatial autocorrelations through eigendecomposition of the spatial weighting matrix.Results
Negative spatial autocorrelation in richness and evenness were more pronounced in the clearcut than uncut sites, although positive spatial autocorrelations in all indices of diversity remained unchanged. Effect of disturbance was not detected on the overall spatial autocorrelation.Conclusions
Disturbance increases negative spatial autocorrelation in species richness and evenness, with a stronger increase in evenness than richness, which underscores the importance of competition in structuring post-disturbance riparian communities. Our results also highlight the need for assessing positive and negative spatial autocorrelation and different aspects of diversity separately in understanding disturbance effects on the spatial pattern, or identifying processes from patterns.7.
We hypothesized that the spatial configuration and dynamics of periurban forest patches in Barcelona (NE of Spain) played
a minor role in determining plant species richness and assemblage compared to site conditions, and particularly to both direct
(measured at plot level) and potential (inferred from landscape metrics) human-associated site disturbance. The presence of
all understory vascular plants was recorded on 252 plots of 100 m2 randomly selected within forest patches ranging in size from 0.25 ha to 218 ha. Species were divided into 6 groups, according
to their ecology and conservation status. Site condition was assessed at plot level and included physical attributes, human-induced
disturbance and Quercus spp. tree cover. Landscape structure and dynamics were assessed from patch metrics and patch history. We also calculated
a set of landscape metrics related to potential human accessibility to forests. Results of multiple linear regressions indicated
that the variance explained for non-forest species groups was higher than for forest species richness. Most of the main correlates
corresponded to site disturbance variables related to direct human alteration, or to landscape variables associated to indirect
human effects on forests: Quercus tree cover (a proxy for successional status) was the most important correlate of non-forest species richness, which decreased
when Quercus tree cover increased. Human-induced disturbance was an important correlate of synanthropic and total species richness, which
were higher in recently managed and in highly frequented forests. Potential human accessibility also affected the richness
of most species groups. In contrast, patch size, patch shape and connectivity played a minor role, as did patch history. We
conclude that human influence on species richness in periurban forests takes place on a small scale, whereas large-scale effects
attributable to landscape structure and fragmentation are comparatively less important. Implications of these results for
the conservation of plant species in periurban forests are discussed. 相似文献
8.
Ecological theory predicts a positive influence of local-, landscape-, and regional-scale spatial environmental heterogeneity
on local species richness. Therefore, knowing how heterogeneity measured at a variety of scales relates to local species richness
has important implications for conservation of biological diversity. We took a statistical modeling approach to determine
which metrics of heterogeneity measured at which scales were useful predictors of local species richness, and whether the
heterogeneity-local richness relationship was always positive. Local plant species richness data came from 400-m2 vegetation plots in North and South Carolina, USA. At each of four scales from within plots to across regions, we used either
GIS or field data to calculate measures of heterogeneity from abiotic environmental variables, vegetation productivity data,
and land cover classifications. Among all predictors at all scales, we found that no measure of heterogeneity was a better
predictor of local richness than mean pH within plots. However, at scales larger than within plots, measures of heterogeneity
were correlated most strongly with local richness, and each of the three classes of variables we used had a distinct scale
at which it performed better than the others. These results highlight the fact that ecological processes occurring across
multiple scales influence local species richness differently. In addition, relationships between heterogeneity and richness
were usually, though not always, positive, underscoring the importance of processes that occur at a variety of scales to local
biodiversity conservation and management. 相似文献
9.
We explored patterns of plant species richness at different spatialscales in 14 habitats in a Swedish rural landscape. Effects of physicalconditions, and relationships between species richness and management historyreaching back to the 17th century were examined, using old cadastralmaps andaerial photographs. The most species-rich habitats were dry open semi-naturalgrasslands, midfield islets and road verges. Alpha diversity (species richnesswithin sites) was highest in habitats on dry substrates (excluding bedrock withsparse pines) and beta diversity (species richness among sites) was highest inmoist to wet habitats. Alpha and beta components of species richness tended tobe inversely related among habitats with similar species richness. Managementhistory influenced diversity patterns. Areas managed as grasslands in the17th and 18th century harboured more species than areasoutside the villages. We also found significant relationships between speciesrichness and soil type. Silt proved to be the most species-rich topsoil(10–20 cm) in addition to thin soils top of on green- orlimestone bedrock. The variation in species richness due to local relief orform of thesite also showed significant relationships, where flat surfaces had the highestnumber of species. In contrast, no significant relationship was found betweenspecies richness and aspect. Our study suggests that present-day diversitypatterns are much influenced by management history, and that small habitat,e.g., road verges and midfield islets, are important for maintaining speciesrichness.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
10.
We developed a spatially-explicit gap dynamics simulation model to evaluate the effects of disturbances at the scale of a landscape for a semiarid grassland in northcentral Colorado, USA. The model simulates the establishment, growth, and death of individual plants on a small plot through time at an annual time step. Long-term successional dynamics on individual plots (single gaps) and on a landscape composed of a grid of plots were evaluated. Landscapes were simulated as either a collection of independent plots or as a collection of interacting plots where processes on one plot were influenced by processes on adjacent plots. Because we were interested in the recovery of the dominant plant species, the perennial grass blue grama (Bouteloua gracilis (H.B.K.) Lag. ex Griffiths) after disturbances, we focused on scale-dependent processes, such as seed dispersal, that are important to the recruitment of individuals of B. gracilis.
The type of simulated landscape was important to the recovery time of B. gracilis after a disturbance. Landscapes composed of independent plots recovered more rapidly following a disturbance than landscapes composed of interacting plots in which the recovery time was dependent on the spatial scale of the disturbance. 相似文献
11.
Kris Van Looy Cyril Cavillon Thierry Tormos Jérémy Piffady Philippe Landry Yves Souchon 《Landscape Ecology》2013,28(7):1239-1249
Existing methods for connectivity analysis still encounter difficulties in explaining functional relationships between network structure and ecological patterns over larger territories or complex structures like dendritic river networks. We propose a method that addresses the problem of scale and resolution in the connectivity analysis of dendritic network structures, illustrated here for the re-colonization of the French Loire river basin by the European otter. The ecological niche factor approach is applied to infer favourable habitat in the river network based on large scale data of land use and hydro-morphology of river segments for the entire river basin. These analyses identified the stressors to the riparian zone of channel straightening, urbanisation and forest fragmentation as the principal factors explaining otter occurrence. Using this estimate of habitat favourability, we used the Integral Index of Connectivity to quantify habitat availability and connectivity in the dendritic river network. When we calculate the integral index of connectivity over different spatial extents by constraining network distances, the scale-sensitivity of the network’s connectivity emerges. Accounting for high mobility by entering larger network distances in the analysis identifies conservation networks and priorities mainly in downstream parts of the river basin, whereas with smaller network distances, more restricted high quality areas in central and upstream parts are highlighted. The presented approach performed better than distribution modelling approaches in explaining species occurrence over the river network and confirms the crucial aspect of connectivity in otter re-colonization. 相似文献
12.
13.
The diversity of future landscapes might depend on our ability to predict their potential species richness. The predictability
of patterns of vascular plant species richness in a Finnish agricultural river landscape was studied using generalized linear
modeling, floristic records from fifty-three0.25-km grid squares in the “core” study area, and environmental variables derived
from Landsat TM images and a digital elevation model. We built multiple regression models for the total number of plant species
and the number of rarities, and validated the accuracy of the derived models with a test set of 52 grid squares. We tentatively
extrapolated the models from the core study area to the whole study area of 601 km2 and produced species richness probability maps using GIS techniques. The results suggest that the local ‘hotspots’ of total
flora (grid squares with > 200species) are mainly found in river valleys, where habitat diversity is high and a semi-open
agricultural-forest mosaic occurs. The ‘hotspots’ of rare species (grid squares with > 4 rare species) are also found in river
valleys, in sites where extensive semi-natural grasslands and herb-rich deciduous forests occur on steep slopes. We conclude
that environmental variables derived from satellite images and topographic data can be used as approximate surrogates of plant
species diversity in agricultural landscapes. Modeling of biological diversity based on satellite images and GIS can provide
useful information needed in land use planning. However, due to the potential pitfalls in processing satellite imagery and
model-building procedures, the results of predictive models should be carefully interpreted.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
The most common technique for establishment of thin extensive green roofs in Sweden has been using prefabricated vegetation mats. Our study investigated (1) how the establishment of green roofs in Sweden was influenced by the establishment method (prefabricated vegetation mat, plug-plant, shoot), substrate composition and species mixture, and (2) whether on-site construction was a possible alternative. The establishment of the vegetation, which in all cases consisted of succulent species, was recorded using the quadrate point intercept method in fixed plots and the success measured as frequency cover.Prefabricated vegetation mats had higher succulent plant cover than on-site constructed roofs. There was no difference in succulent plant cover between plots established using plug-plants compared to shoots. Shoot-established plots had more moss than the other establishment methods. The commercial substrate ‘Roof soil’ had significantly higher succulent plant cover than the other substrates, which might be related to a higher nutrient content. The organic content of the non-commercial substrates was rapidly decomposed. The standard species mixture produced a higher cover than both the mix developed for northern conditions and the mix with an increased proportion of big leaved species. The total cover of the plots was mainly dependent on the cover of two species: Sedum album (L.) and Sedum acre (L.). Few species managed to establish spontaneously but the establishment of woody species highlighted the need for proper maintenance. 相似文献
15.
Felipe Rossetti de Paula Pedro Gerhard Seth J. Wenger Anderson Ferreira Carlos Alberto Vettorazzi Silvio Frosini de Barros Ferraz 《Landscape Ecology》2013,28(1):13-27
Large wood (LW) is critical to the structure and function of streams and forests are the main LW source to stream channels. To assess the influence of forest cover changes at different spatial scales on in-stream LW quantity, we selected eighteen catchments (2nd–4th order) in Southeastern Brazil with forests at different levels of alterations. In each catchment we quantified the pattern of forest cover (% cover and relative catchment position), the physical characteristics of catchments (elevation and slope), the characteristics of channels (wetted channel width and depth), the abundance and volume of in-stream LW, and the frequency of LW pools. We used simple and multiple linear regression to assess the response of LW variables to landscape and stream reach variables. Most of the LW was relatively small; 72 % had a diameter <20 cm, and 66 % had a length <5 m. Although percent forest cover at reach scale had substantial support to explain LW variables, the best predictors of LW variables were forest cover at broader scales (LW abundance and LW pool frequency were best predicted by forest at intermediate distance at the catchment scale and LW volume was best predicted by forest cover at the drainage network scale), suggesting that downstream transport is an important process in addition to local processes in our study area. These findings have important management implications because although low forested reaches receive less LW from local forests (or no LW in the case of deforested stream reaches), they are receiving LW from upstream forested reaches. However, the material is generally small, unstable and likely to be easily flushed. This suggests that not only should riparian forest conservation encompass the full drainage network, but forests should also be allowed to regenerate to later successional stages to provide larger, higher quality LW for natural structuring of streams. 相似文献
16.
Understanding the determinants of hedgerow plant diversity in agricultural landscapes remains a difficult task, because the
potential drivers affect the complete range of biodiversity components (alpha to gamma diversity). We surveyed herbaceous
plant communities (of a height <1.5 m) in 84 hedgerows in the Seine river floodplain of France. Two types of potential drivers
for species richness, accounting for landscape mosaic and hedgerow network, were recorded at both hedgerow and site scale.
The distribution of species richness through the components of alpha hedgerow diversity (i.e. the average diversity within
a habitat) and gamma hedgerow diversity (i.e. the total diversity across habitats) were assessed using additive partitioning
methods, while the relationship between species diversity and its potential landscape drivers at both scales was modeled using
Generalized Additive Models. Our results indicated that gamma hedgerow diversity is explained by the heterogeneity of the
landscape structure, which is correlated with the mosaic of agricultural land use. At this scale, intrinsic properties of
the configuration of the hedgerow networks have a weak influence on species richness. Alpha hedgerow diversity is also explained
by landscape variables, accounting for both the configuration of agricultural mosaics and hedgerow networks, but to a lesser
extent. Time lags for species responses are shown at both scales, and for the two types of drivers. Extinction or colonization
debt may be indicated at both scales, while the remnant effects of former practices may also be responsible for such patterns
at a local scale. We suggest that hedgerow management should take the specific parameters of both scales into account. At
a local scale, management actions should aim to decrease the influence of adjacent land use when the impact is negative, through
the implementation of extended buffer zones, while at the landscape and farm scales, agri-environmental schemes should be
dedicated to the conservation of specific agricultural land uses. 相似文献
17.
Context
The relative importance of habitat area and connectivity for species richness is often unknown. Connectivity effects may be confounded with area effects or they may be of minor importance as posited by the habitat-amount hypothesis.Objectives
We studied effects of habitat area and connectivity of linear landscape elements for plant species richness at plot level. We hypothesized that connectivity of linear landscape elements, assessed by resistance distance, has a positive effect on species richness beyond the effect of area and, further, that the relative importance of connectivity varies among groups of species with different habitat preferences and dispersal syndromes.Methods
We surveyed plant species richness in 50 plots (25 m2) located on open linear landscape elements (field margins, ditches) in eight study areas of 1 km2 in agricultural landscapes of Northwest Germany. We calculated the area of linear landscape elements and assessed their connectivity using resistance distance within circular buffers (500 m) around the plots. Effects of area and connectivity on species richness were modelled with generalised linear mixed models.Results
Species richness did not increase with area. Resistance distance had significant negative effects on total richness and on the richness of typical species of grasslands and wetlands. Regarding dispersal syndromes, resistance distance had negative effects on the richness of species with short-distance, long-distance and aquatic dispersal. The significant effects of resistance distance indicated that species richness increased with connectivity of the network of linear landscape elements.Conclusions
Connectivity is more important for plant species richness in linear landscape elements than area. In particular, the richness of plant species that are dispersal limited and confined to semi-natural habitats benefits from connective networks of linear landscape elements in agricultural landscapes.18.
Contemporary landscape ecology continues to explore the causes and consequences of landscape heterogeneity across a range of scales, and demands for the scientific underpinnings of landscape planning and management still remains high. The spatial distribution of resources can be a key element in determining habitat quality, and that in turn is directly related to the level of heterogeneity in the system. In this sense, forest habitat mosaics may be more affected by lack of heterogeneity than by structural fragmentation. Nonetheless, increasing spatial heterogeneity at a given spatial scale can also decrease habitat patch size, with potential negative consequences for specialist species. Such dual effect may lead to hump-backed shape relationships between species diversity and heterogeneity, leading to three related assumptions: (i) at low levels of heterogeneity, an increase in heterogeneity favours local and regional species richness, (ii) there is an optimum heterogeneity level at which a maximum number of species is reached, (iii) further increase in spatial heterogeneity has a negative effect on local and regional species richness, due to increasing adverse effects of habitat fragmentation. In this study, we investigated the existence of a hump-shaped relationship between local plant species richness and increasing forest landscape heterogeneity on a complex mosaic in the French Alps. Forest landscape heterogeneity was quantified with five independent criteria. We found significant quadratic relationships between local forest species richness and two heterogeneity criteria indicators, showing a slight decrease of forest species richness at very high heterogeneity levels. Species richness–landscape heterogeneity relationships varied according to the heterogeneity metrics involved and the type of species richness considered. Our results support the assumption that intermediate levels of heterogeneity may support more species than very high levels of heterogeneity, although we were not able to conclude for a systematic negative effect of very high levels of heterogeneity on local plant species richness. 相似文献
19.
Traditional agricultural mosaic landscapes are likely to undergo dramatic changes through either intensification or abandonment
of land use. Both developmental trends may negatively affect the vascular plant species richness of such landscapes. Therefore,
sustainable land-use systems need to be developed to maintain and re-establish species richness at various spatial scales.
To evaluate the sustainability of specific land-use systems, we need approaches for the effective assessment of the present
species richness and models that can predict the effects on species richness as realistically as possible. In this context,
we present a methodology to estimate and predict vascular plant species richness at the local and the regional scale. In our
approach, the major determinants of vascular plant species richness within the study area are taken into consideration: These
are according to Duelli's mosaic concept the number of habitat types and of habitat patches within area units. Furthermore,
it is based on the relative frequencies of species within habitat types. Our approach comprises six steps: (i) the determination
of present habitat patterns within an observation area, (ii) the creation of a land-use scenario with simulated habitat patterns,
(iii) the determination of species frequencies within habitat types of this area, (iv) a grouping of habitat-specific species,
(v) the estimation of the probabilities for all species (or habitat specialists) to occur, either in stepwise, exponentially
enlarged landscape tracts (local scale), or in the entire observation area (regional scale), and (vi) the validation of the
estimated species numbers. The approach will be exemplified using data from the municipal district of Erda, Lahn-Dill Highlands,
Germany. The current species numbers to be expected on the basis of probability calculations were compared with those recorded
on the basis of extensive field work. This comparison shows that, on the basis of our simple calculations, the current local
plant species richness can be predicted well, with a slight underestimation.
This revised version was published online in May 2005 with corrections to the Cover Date.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
20.
Herbivores influence the structure of plant communities in arctic-alpine ecosystems. However, little is known of the effect of herbivores on plant colonisation following disturbance, and on its variability depending on the identity of herbivores and the characteristics of the habitats. To quantify the role of large and small vertebrate herbivores, we established exclosures of two different mesh sizes around disturbed subplots in forest and nearby tundra habitats in four contrasting locations in the forest-tundra ecotone in northernmost Sweden and Norway. The study revealed that herbivores influenced the abundance but not the species composition of regenerating vegetation. Gaps were colonised by the dominant species in the surrounding vegetation. The only exception to this expectation was Empetrum nigrum, which failed to colonise gaps even though it dominated undisturbed vegetation. Significant effects of herbivory were only detected when both small and large herbivores were excluded. Herbivores decreased the abundance of three of the most common species Vaccinium myrtillus, Vaccinium vitis idaea, and Deschampsia flexuosa. The effect of herbivory on the abundance of these three species did not differ between habitats and locations. However, the composition of the regenerating vegetation differed between habitats and locations. The disturbance treatment increased the species richness on the scale of plots, habitats, and sites. However, on the scale of whole locations, all species found in disturbed areas were also found in undisturbed areas, suggesting that the natural disturbance regime in arctic landscapes is high enough to sustain colonising species. 相似文献