共查询到20条相似文献，搜索用时 31 毫秒
1.
Selection of scale for Everglades landscape models 总被引：3，自引：0，他引：3
This article addresses the problem of determining the optimal “Model Grain” or spatial resolution (scale) for landscape modeling
in the Everglades. Selecting an appropriate scale for landscape modeling is a critical task that is necessary before using
spatial data for model development. How the landscape is viewed in a simulation model is dependent on the scale (cell size)
in which it is created. Given that different processes usually have different rates of fluctuations (frequencies), the question
of selection of an appropriate modeling scale is a difficult one and most relevant to developing spatial ecosystem models.
The question of choosing the appropriate scale for modeling is addressed using the landscape indices (e.g., cover fraction, diversity index, fractal dimension, and transition probabilities) recently developed for quantifying overall
characteristics of spatial patterns. A vegetation map of an Everglades impoundment area developed from SPOT satellite data
was used in the analyses. The data from this original 20 × 20 m data set was spatially aggregated to a 40 × 40 m resolution
and incremented by 40 meters on up to 1000 × 1000 m (i.e., 40, 80, 120, 160 … 1000) scale. The primary focus was on the loss of information and the variation of spatial indices as
a function of broadening “Model Grain” or scale.
Cover fraction and diversity indices with broadening scale indicate important features, such as tree islands and brush mixture
communities in the landscape, nearly disappear at or beyond the 700 m scale. The fractal analyses indicate that the area perimeter
relationship changes quite rapidly after about 100 m scale. These results and others reported in the paper should be useful
for setting appropriate objectives and expectations for Everglades landscape models built to varying spatial scales. 相似文献
2.
Robert H. Gardner Todd R. Lookingbill Philip A. Townsend Joseph Ferrari 《Landscape Ecology》2008,23(5):513-526
The resolution of satellite imagery must often be increased or decreased to fill data gaps or match preexisting project requirements.
It is well known that a change in resolution introduces systematic errors of size, shape, location and amount of contiguous
land cover types. Nevertheless, robust methods for rescaling landscape data are frequently required to assess patterns of
landscape change through time and over large areas. We developed a new method for rescaling spatial data that allows map resolution
(grain size) to be either increased or decreased while holding the total proportion of land cover types constant. The method
uses a weighted sampling net of variable resolution to sample an existing map and then randomly selects from the frequency
of cover types derived from this sample to assign the cover type for the corresponding location in the rescaled map. The properties
of the sampling net had a variable effect on measures of landscape pattern with the characteristic patch size (S) the most robust metric and the number of clusters (A) the most variable. A comparison of up-scaled and down-scaled maps showed that this process is not symmetrical, producing
different errors for increases versus decreases in grain size. Rescaling Landsat (30 m) imagery to the 10 m resolution of
SPOT imagery for four National Park units within Maryland and Virginia resulted in errors due to rescaling that were small
(1–2%) relative to the total error (∼11%) associated with these images. The new rescaling method is general because it provides
a single method for increasing or decreasing resolution, can be applied to maps with multiple land cover types, allows grid
geometry to be transformed (i.e., square to hexagonal grids), and provide a more consistent basis for landscape comparisons
when maps must be derived from multiple sources of classified imagery. 相似文献
3.
Because organisms respond to the environment at different scales, it is important to develop ways of determining the appropriate
scales for a specific ecological process and organism. We consider whether the relative importance of different scales is
associated with organism mobility, and whether this relationship is independent of landscape characteristics. We observed
abundances of particular species for vascular plants, ground-dwelling beetles and breeding birds along eight 2-km transects
of 40 sampling stations each, distributed over four sites along the regional gradient from shortgrass steppe in central Colorado
to tallgrass prairie in central Kansas. For each transect and taxonomic group, the relative importance of factors measured
at the trap scale (1 m; soil texture and hardness, vegetation height, bare ground), at the local scale (10 m; density of shrubs
and cacti) and at the landscape scale (30 m; Landsat 7 TM spectral bands, slope and elevation) was assessed using hierarchical
canonical variance partitioning with forward selection of explanatory variables. Plant, beetle and bird community composition
was explained by environmental factors measured at all three scales. Factor influence was more consistent between transects
and between plants and beetles for the more homogeneous landscapes of the shortgrass steppe than for the more heterogeneous
landscapes of the tallgrass prairie. We conclude that, independent of the mobility of a taxonomic group, factors at several
scales are important in explaining community composition. The importance of different scales shifts along a regional gradient,
and the variability between sites is high even for nearby sites. 相似文献
4.
Alternative spatial resolutions and estimation of carbon flux over a managed forest landscape in Western Oregon 总被引：4，自引：0，他引：4
Spatially-distributed estimates of biologically-driven CO2 flux are of interest in relation to understanding the global carbon cycle. Global coverage by satellite sensors offers an opportunity to assess terrestrial carbon (C) flux using a variety of approaches and corresponding spatial resolutions. An important consideration in evaluating the approaches concerns the scale of the spatial heterogeneity in land cover over the domain being studied. In the Pacific Northwest region of the United States, forests are highly fragmented with respect to stand age class and hence C flux. In this study, the effects of spatial resolution on estimates of total annual net primary production (NPP) and net ecosystem production (NEP) for a 96 km2 area in the central Cascades Mountains of western Oregon were examined. The scaling approach was a simple `measure and multiply' algorithm. At the highest spatial resolution (25 m), a stand age map derived from Landsat Thematic Mapper imagery provided the area for each of six forest age classes. The products of area for each age class and its respective NPP or NEP were summed for the area wide estimates. In order to evaluate potential errors at coarser resolutions, the stand age map was resampled to grain sizes of 100, 250, 500 and 1000 m using a majority filter reclassification. Local variance in near-infrared (NIR) band digital number at successively coarser grain sizes was also examined to characterize the scale of the heterogeneity in the scene. For this managed forest landscape, proportional estimation error in land cover classification at the coarsest resolution varied from –1.0 to +0.6 depending on the initial representation and the spatial distribution of the age class. The overall accuracy of the 1000 m resolution map was 42% with respect to the 25 m map. Analysis of local variance in NIR digital number suggested a patch size on the order of 100–500 m on a side. Total estimated NPP was 12% lower and total estimated NEP was 4% lower at 1000 m compared to 25 m. Carbon flux estimates based on quantifying differences in total biomass stored on the landscape at two points in time might be affected more strongly by a coarse resolution analysis because the differences among classes in biomass are more extreme than the differences in C flux and because the additional steps in the flux algorithm would contribute to error propagation. Scaling exercises involving reclassification of fine scale imagery over a range of grain sizes may be a useful screening tool for stratifying regions of the terrestrial surface relative to optimizing the spatial resolution for C flux estimation purposes. 相似文献
5.
Emmanuelle Sebert-Cuvillier Valérie Simon-Goyheneche Frédéric Paccaut Olivier Chabrerie Olivier Goubet Guillaume Decocq 《Landscape Ecology》2008,23(7):787-801
The effect of environmental heterogeneity on spatial spread of invasive species has received little attention in the literature.
Altering landscape heterogeneity may be a suitable strategy to control invaders in man-made landscapes. We use a population-based,
spatially realistic matrix model to explore mechanisms underlying the observed invasion patterns of an alien tree species,
Prunus serotina Ehrh., in a heterogeneous managed forest. By altering several parameters in the simulation, we test for various hypotheses regarding
the role of several mechanisms on invasion dynamics, including spatial heterogeneity, seed dispersers, site of first introduction,
large-scale natural disturbances, and forest management. We observe that landscape heterogeneity makes the invasion highly
directional resulting from two mechanisms: (1) irregular jumps, which occur rarely via long-distance dispersers and create
new founder populations in distant suitable areas, and (2) regular, continuous diffusion toward adjacent cells via short-
and mid-distance vectors. At the landscape scale, spatial heterogeneity increases the invasion speed but decreases the final
invasion extent. Hence, natural disturbances (such as severe storms) appear to facilitate invasion spread, while forest management
can have contrasting effects such as decreasing invasibility at the stand scale by increasing the proportion of light interception
at the canopy level. The site of initial introduction influences the invasion process but without altering the final outcome.
Our model represents the real landscape and incorporates the range of dispersal modes, making it a powerful tool to explore
the interactions between environmental heterogeneity and invasion dynamics, as well as for managing plant invaders.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
6.
Chen Jiquan Sciusco Pietro Ouyang Zutao Zhang Rong Henebry Geoffrey M. John Ranjeet Roy David. P. 《Landscape Ecology》2019,34(12):2917-2934
Context
The open and free access to Landsat and MODIS products have greatly promoted scientific investigations on spatiotemporal change in land mosaics and ecosystem functions at landscape to regional scales. Unfortunately, there is a major mismatch in spatial resolution between MODIS products at coarser resolution (≥?250 m) and landscape structure based on classified Landsat scenes at finer resolution (30 m).
ObjectivesBased on practical needs for downscaling popular MODIS products at 500 m resolution to match classified land cover at Landsat 30 m resolution, we proposed an innovative modelling approach so that landscape structure and ecosystem functions can be directly studied for their interconnections. As a proof-of-concept of our downscaling approach, we selected the watershed of the Kalamazoo River in southwestern Michigan, USA as the testbed.
MethodsMODIS products for three fundamental variables of ecosystem function are downscaled to ensure the approach can be extrapolated to multiple functional measurements. They are blue-sky albedo (0–1), evapotranspiration (ET, mm), and gross primary production (GPP, Mg C ha?1 year?1). An object-oriented classification of Landsat images in 2011 was processed to generate a land cover map for landscape structure. The downscaling model was tested for the five Level IV ecoregions within the watershed.
ResultsWe achieved satisfactory downscaling models for albedo, ET, and GPP for all five ecoregions. The adjusted R2 was?>?0.995 for albedo, 0.915–0.997 for ET, and 0.902–0.962 for GPP. The estimated albedo, ET, and GPP values appear different in the region. The estimated albedo was the lowest for water (0.076–0.107) and the highest for cropland (0.166–0.172). Estimated ET was the highest for the built-up cover type (525.6–687.1 mm) and the lowest for forest (209.7–459.7 mm). The estimated GPP was the highest for the build-up cover type (8.65–9.85 Mg C ha?1 year?1) and the lowest for forest.
ConclusionsEstimated values for albedo, ET, and GPP appear reasonable for their ranges in the Kalamazoo River region and are consistent with values reported in the literature. Despite these promising results, the downscaling approach relies on strong assumptions and can carry substantial uncertainty. It is only valid at a spatial scale where similar climate, soil, and landforms exist (i.e., values in isolated patches of the same cover type are similar). Plausibly, the uncertainties associated with each estimation, as well as the model residuals, can be explored for other pattern-process relationships within the landscape.
相似文献7.
General Land Office Survey (GLOS) records from the A.D. 1840s provide data for quantitative characterization of presettlement
vegetation across western Mackinac County, Michigan, located within the mixed conifer-northern hardwoods forest region. We
analyzed data from land survey plat maps and 1958 bearing, witness, and line trees from 162 surveyed section and quarter-section
corners in order to map vegatation cover types at a level of spatial resolution appropriate for characterizing landscape heterogeneity
using standard landscape ecological metrics. As also demonstrated by a number of both classic and contemporary plant-ecological
studies, the distribution of landforms, soils properties, hydrology, and location of fire breaks all contribute to the heterogeneity
in vegetation observed at a landscape scale in the region. Through a series of spatial landscape analyses with differing grain
of resolution, in this study we determine that a grid cell size of 65 ha (0.5 mi×0.5 mi or 0.25 mi2) to 259 ha (1 mi2) gives a conservative characterization of landscape heterogeneity using standard metrics and is therefore appropriate for
use of GLOS data to study historical landscape changes. 相似文献
8.
In the North American upper Great Lakes region, forests dominated by the aspens (Populus grandidentata Michx. – bigtooth aspen, and P. tremuloides Michx. – trembling aspen), which established after late 19th and early 20th century logging, are maturing and succession
will create a new forest composition at landscape to regional scales. This study analyzed the capabilities of Landsat ETM+
remote sensing data combined with existing ecological land unit classifications to discriminate and quantify patterns of succession
at the landscape scale over the 4200 ha University of Michigan Biological Station (UMBS) in northern Lower Michigan. In a
hierarchical approach first multi-temporal Landsat ETM+ was used with a landscape ecosystem classification to map upland forest
cover types (overall accuracy 91.7%). Next the aspen cover type was subset and successional pathways were mapped within that
type (overall accuracy 89.8%). Results demonstrated that Landsat ETM+ may be useful for these purposes; stratification of
upland from wetland types using an ecological land unit classification eliminated confounding issues; multi-temporal methods
discriminated evergreen conifer versus deciduous understories. The Landsat ETM+ classifications were then used to quantify
succession and its relationship to landform-level ecological land units. Forests on moraine and ice contact landforms are
succeeding distinctly to northern hardwoods (95% and 88% respectively); those on outwash and other landforms show greater
diversity of successional pathways. 相似文献
9.
Based on the agricultural landscape of the Sebungwe in Zimbabwe, we investigated whether and how the spatial distribution of the African elephant (Loxodonta africana) responded to spatial heterogeneity of vegetation cover based on data of the early 1980s and early 1990s. We also investigated whether and how elephant distribution responded to changes in spatial heterogeneity between the early 1980s and early 1990s. Vegetation cover was estimated from a normalised difference vegetation index (NDVI). Spatial heterogeneity was estimated from a new approach based on the intensity (i.e., the maximum variance exhibited when a spatially distributed landscape property such as vegetation cover is measured with a successively increasing window size or scale) and dominant scale (i.e., the scale or window size at which the intensity is displayed). We used a variogram to quantify the dominant scale (i.e., range) and intensity (i.e., sill) of NDVI based congruent windows (i.e., 3.84 km × 3.84 km in a 61 km × 61 km landscape). The results indicated that elephants consistently responded to the dominant scale of spatial heterogeneity in a unimodal fashion with the peak elephant presence occurring in environments with dominant scales of spatial heterogeneity of around 457–734 m. Both the intensity and dominant scale of spatial heterogeneity predicted 65 and 68% of the variance in elephant presence in the early 1980s and in the early 1990s respectively. Also, changes in the intensity and dominant scale of spatial heterogeneity predicted 61% of the variance in the change in elephant distribution. The results imply that management decisions must take into consideration the influence of the levels of spatial heterogeneity on elephants in order to ensure elephant persistence in agricultural landscapes. 相似文献
10.
Context
Arid rangelands have been severely degraded over the past century. Multi-temporal remote sensing techniques are ideally suited to detect significant changes in ecosystem state; however, considerable uncertainty exists regarding the effects of changing image resolution on their ability to detect ecologically meaningful change from satellite time-series.Objectives
(1) Assess the effects of image resolution in detecting landscape spatial heterogeneity. (2) Compare and evaluate the efficacy of coarse (MODIS) and moderate (Landsat) resolution satellite time-series for detecting ecosystem change.Methods
Using long-term (~12 year) vegetation monitoring data from grassland and shrubland sites in southern New Mexico, USA, we evaluated the effects of changing image support using MODIS (250-m) and Landsat (30-m) time-series in modeling and detecting significant changes in vegetation using time-series decomposition techniques.Results
Within our study ecosystem, landscape-scale (>20-m) spatial heterogeneity was low, resulting in a similar ability to detect vegetation changes across both satellite sensors and levels of spatial image support. While both Landsat and MODIS imagery were effective in modeling temporal dynamics in vegetation structure and composition, MODIS was more strongly correlated to biomass due to its cleaner (i.e., fewer artifacts/data gaps) 16-day temporal signal.Conclusions
The optimization of spatial/temporal scale is critical in ensuring adequate detection of change. While the results presented in this study are likely specific to arid shrub-grassland ecosystems, the approach presented here is generally applicable. Future analysis is needed in other ecosystems to assess how scaling relationships will change under different vegetation communities that range in their degree of landscape heterogeneity.11.
Scale problems in reporting landscape pattern at the regional scale 总被引：30，自引：2，他引：28
R. V. O'Neill C. T. Hunsaker S. P. Timmins B. L. Jackson K. B. Jones K. H. Riitters J. D. Wickham 《Landscape Ecology》1996,11(3):169-180
Remotely sensed data for Southeastern United States (Standard Federal Region 4) are used to examine the scale problems involved
in reporting landscape pattern for a large, heterogeneous region. Frequency distributions of landscape indices illustrate
problems associated with the grain or resolution of the data. Grain should be 2 to 5 times smaller than the spatial features
of interest. The analyses also reveal that the indices are sensitive to the calculation scale,i.e., the unit area or extent over which the index is computed. This “sample area” must be 2 to 5 times larger than landscape
patches to avoid bias in calculating the indices.
Research sponsored by the Office of Research and Development, U.S. Environmental Protection Agency under IAG DW89934440-6
and DW89936104-01 with the U.S. Department of Energy under contract DE-AC05-84OR21400 with Martin Marietta Energy Systems,
Inc. 相似文献
12.
Detailed species composition data are rapidly collected using a high-powered telescope from remote vantage points at two scales: site level and patch level. Patches constitute areas of homogeneous vegetation composition. Multiple samples of species composition are randomly located within the patches. These data are used as site-level data and are also aggregated to provide species composition data at the patch level. The site- and patch-level data are spatially integrated with high resolution (10 m), topographically-derived fields of environmental conditions, such as solar radiation, air temperature, and topographic moisture index in order to evaluate the applicability of the sampling method for modeling relationships between species composition and environmental processes.The methodology provides a balance between sampling efficiency and the accuracy of field data. Application of the method is appropriate for environments where terrain and canopy characteristics permit open visibility of the landscape. We evaluate the nature of data resulting from an implementation of the remote sampling methodology in a steep watershed dominated by closed-canopy chaparral. Analyses indicate that there is minimal bias associated with scaling the data from the site level to the patch level, despite variable patch sizes. Analysis of variance and correlation tests show that the internal floristic and environmental variability of patches is low and stable across the entire sample of patches. Comparison of regression tree models of species cover at the two scales indicates that there is little scale-dependence in the ecological processes that govern patterns of species composition between the site level and patch level. High explanatory power of the regression tree models suggests that the vegetation data are characterized at an appropriate scale to model landscape-level patterns of species composition as driven by topographically-mediated processes. Patch-level sampling reduces the influence of local stochasticity and micro-scale processes. Comparison of models between the two scales can be useful for assessing the processes and associated scales of variability governing spatial patterns of plant species. 相似文献
13.
14.
Sensitivity of landscape pattern indices to input data characteristics on real landscapes: implications for their use in natural disturbance emulation 总被引：17，自引：6，他引：11
Baldwin David J. B. Weaver Kevin Schnekenburger Frank Perera Ajith H. 《Landscape Ecology》2004,19(3):255-271
Resource management strategies have begun to adopt natural landscape disturbance emulation as a means of minimizing risk to ecosystem integrity. Detailed understanding of the disturbance regime and the associated spatial landscape patterns are required to provide a natural baseline for comparison with the results of emulation strategies. Landscape pattern indices provide a useful tool to quantify spatial pattern for developing these strategies and evaluating their success. Despite an abundance of indices and tools to calculate these, practical knowledge of interpretation is rare. Quantifying changes in landscape pattern indices and the meaning of these changes is confounded by index sensitivity to input data characteristics such as spatial extent, spatial resolution, and thematic resolution. Sensitivity has been examined for simulated landscapes but rarely using real data for large areas as real landscapes are more difficult to manipulate systematically than simulated data. While simulated data offer a control, they do not provide an accurate portrayal of reality for practical applications. Our goal was to test the sensitivity of a suite of landscape pattern indices useful for disturbance emulation strategy development and evaluation to spatial extent, spatial resolution, and thematic resolution using current land cover data for a case study of the managed forest of Ontario, Canada. We also examined how sensitivity varies spatially across the study area. We used Landsat TM-based land cover data (> 45.5 million ha), controlling spatial extent (2,500 to 2,560,000 ha), spatial resolution (1 to 16 ha), and thematic resolution (2 to 26 classes). For each index we tested a hypothesis of insensitivity to changes in each input data characteristic using a combination of ANOVA and regression and compared our results with previous studies. Of the 18 indices studied, significant (p< 0.01) effects were found for 17 indices with changes in spatial extent, 13 indices with changes in spatial resolution and 18 indices with changes in thematic resolution. A significant (p < 0.01) linear trend accounted for the majority of the variance for all of the significant relationships identified. Most of the mean index responses were consistent with those interpreted from previous studies of simulated and real landscapes; however, sensitivity varied greatly among indices and over space. We suggest that variation in sensitivity to input data characteristics among indices and over space must be explicitly incorporated in the design of future natural disturbance emulation efforts.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
15.
Animals may respond to spatial and temporal heterogeneity by altering their movement patterns. The time an animal spends in an area of a given size is termed ȁ8first-passage timeȁ9 and can be used to identify the scales at which different movement processes occur. Using first-passage time and 2-h observations, we identified nested spatial scales representing three movement behaviours for elk (Cervus elaphus) – inactive/resting (moves < 50 m), active/foraging (x̄ = 276.7 m, SD = 56.6), and active/relocating (x̄ = 1628.3 m, SD = 436.6). Our ability to identify inactive behaviour was limited by GPS accuracy. The scale separating relocating and foraging behaviour ranged 550–1650 m across individuals and varied quadratically with the mean patch size of cutover forest in an animal’s home range. We classified path segments into the 3 movement behaviours and related behaviours to local environmental conditions. Elk were likely to be inactive in areas having a low predicted use by wolves (Canis lupus), farther than 50 m from anthropogenic linear clearings, and where microclimatic conditions were cool (high shrub cover and north to east-facing slopes). In contrast, elk were most likely to forage in areas having intermediate levels of herbaceous biomass and low movement costs. Elk were most likely to be relocating when in areas of high wolf use, when close to linear clearings, and in energetically costly situations such as moving upslope. We discuss how elk use of potential foraging habitats may be restricted in this landscape by risks imposed by predators, humans, or both. 相似文献
16.
Burrowing mammals create disturbances that increase the ecological heterogeneity of landscapes. In desert systems, banner-tailed kangaroo rats (Dipodomys spectabilis) construct large mounds that greatly influence the spatial patterning of soils, plants, and animals. The overall effects of the patches generated by D. spectabilis depend on the dispersion patterns of the mounds; these patterns may be sensitive to scale and landscape position. We examined the distribution of D. spectabilis mounds across multiple scales in four 40-ha grassland plots in New Mexico, USA. We used Ripley's K-function for our point-pattern analysis. The dispersion patterns of mounds were generally scale-sensitive but depended somewhat on plot-level densities, which were related to topographic position and grazing history. Mound spacing was either regular or random at small scales (0–50 m), random or aggregated at intermediate scales (50–300 m), and aggregated at large scales (300–3000 m). This scale-dependency of pattern reflected spatial domains in which different biotic (territoriality, dispersal, grazing) and abiotic (soil texture and drainage) factors exerted strong influences. How other organisms perceive the spatial patterning of mounds will depend on the extent of their movements. Patches may appear regular to one species but aggregated to another. The dispersion of D. spectabilis mounds also has implications for the spatial structuring of desert rodent communities. D. spectabilis excludes smaller species of kangaroo rats from areas around their mounds; they create spatial heterogeneity in behavioral dominance that may influence the distribution of subordinate species at multiple scales. 相似文献
17.
Regional land-cover change affects biodiversity, hydrology, and biogeochemical cycles at local, watershed, and landscape scales.
Developing countries are experiencing rapid land cover change, but assessment is often restricted by limited financial resources,
accessibility, and historical data. The assessment of regional land cover patterns is often the first step in developing conservation
and management plans. This study used remotely sensed land cover and topographic data (Landsat and Shuttle Radar Topography
Mission), supervised classification techniques, and spectral mixture analysis to characterize current landscape patterns and
quantify land cover change from 1985 to 2003 in the Altiplano (2535–4671 m) and Intermediate Valley (Mountain) (1491–4623 m)
physiographic zones in the Southeastern Bolivian Andes. Current land cover was mapped into six classes with an overall accuracy
of 88% using traditional classification techniques and limited field data. The land cover change analysis showed that extensive
deforestation, desertification, and agricultural expansion at a regional scale occurred in the last 20 years (17.3% of the
Mountain Zone and 7.2% of the Altiplano). Spectral mixture analysis (SMA) indicated that communal rangeland degradation has
also occurred, with increases in soil and non-photosynthetic vegetation fractions in most cover classes. SMA also identified
local areas with intensive management activities that are changing differently from the overall region (e.g., localized areas
of increased green vegetation). This indicates that actions of local communities, governments, and environmental managers
can moderate the potentially severe future changes implied by the results of this study. 相似文献
18.
Wildfires and landscape patterns in the Eastern Iberian Peninsula 总被引：12，自引：2，他引：10
Lloret Francisco Calvo Eduard Pons Xavier Díaz-Delgado Ricardo 《Landscape Ecology》2002,17(8):745-759
The relations between disturbance regime and landscape patterns have been developed from a theoretical perspective, but few studies have tested these relations when forces promoting opposing heterogeneity patterns are simultaneously operating on a landscape. This work provides quantitative evidence of these relations in areas dominated by human activity, showing that landscape heterogeneity decreases disturbance spread. In turn, disturbance introduces a source of landscape heterogeneity, but it is not enough to counterbalance the homogeneity trend due to agricultural abandonment. Land cover changes and wildfire occurrence (fires larger than 0.3 km2) have been monitored in the Tivissa municipality (208.4 km2) (Catalonia, NE Spain) from 1956 to 1993. Land cover maps were obtained from 1956, 1978 and 1993 and they were overlaid with fire occurrence maps obtained for the 1975–1995 period from 60 m resolution remote sensing images, which allow the identification of burned areas by sudden drops in Normalized Difference Vegetation Index (NDVI). Changes in landscape patterns in relation to fire regime have been analyzed considering several parameters: patch density, mean patch size, mean distance to the nearest neighbour of the same category, edge density, and the Shannon diversity index. In the 1956–1993 period there is a trend to increasing landscape homogenization due to the expansion of shrublands linked to a decrease in forest surface, and to the abandonment of agricultural lands. This trend, however, is not constant along all the period. Fires are more likely to occur in woody, homogenous areas, increasing landscape heterogeneity, as observed in the 1978–1993 period. This increase in heterogeneity does not counterbalance the general trend to landscape homogenization as a consequence of agricultural abandonment and the coalescence of natural vegetation patches.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
19.
Assessing the associations between spatial patterns in population abundance and environmental heterogeneity is critical for understanding various population processes and for managing species and communities. This study evaluates responses in the abundance of the European rabbit (Oryctolagus cuniculus), an important prey for predators of conservation concern in Mediterranean ecosystems, to environmental heterogeneity at different spatial scales. Multi-scale habitat models of rabbit abundance in three areas of Doñana, south-western Spain, were developed using a spatially extensive dataset of faecal pellet counts as an abundance index. The best models included habitat variables at the three spatial scales examined: distance from lagoons (broad scale), mean landscape shrub coverage and interspersion of pastures (home-range scale), and shrub and pasture cover (microhabitat scale). These variables may well have been related to the availability of food and refuge for the species at the different scales. However, the models’ fit to data and their predictive accuracy for an independent sample varied among the study regions. Accurate predictions in some areas showed that the combination of variables at various spatial scales can provide a reliable method for assessing the abundance of ecologically complex species such as the European rabbit over large areas. On the other hand, the models failed to identify abundance patterns in a population that suffered the strongest demographic collapse after viral epidemics, underlining the difficulty of generalizing this approach. In the latter case, factors difficult to implement in static models such as disease history and prevalence, predator regulation and others may underlie the lack of association. Habitat models can provide useful guidelines for the management of landscape attributes relevant to rabbits and help improve the conservation of Mediterranean communities. However, other influential factors not obviously related to environmental heterogeneity should also be analyzed in more detail. 相似文献
20.
The distribution and abundance of species are shaped by local and landscape processes, but the dominant processes may differ
with scale and increasing human disturbance. We investigated population responses of two pool-breeding amphibian species to
differences in local and landscape characteristics in suburbanizing, southeastern New Hampshire, USA. In 2003 and 2004, we
sampled 49 vernal pools for spotted salamander (Ambystoma maculatum) and wood frog (Lithobates sylvaticus) egg masses. Using egg masses as a proxy for breeding-female population size, we examined the relative influence of five
land-use and three isolation variables at two scales (300 and 1000 m) and five wetland variables on egg-mass abundance. For
both species, road density at the landscape scale (1000 m) and hydroperiod most strongly predicted egg-mass abundance, with
abundance decreasing as roads became denser and hydroperiods shortened. Wetland isolation was also an important predictor,
with abundance greatest at more isolated pools, suggesting that both species concentrate at isolated pools when alternative
breeding sites are scarce. Surprisingly, no 300-m parameters were strongly associated with salamander egg-mass abundance,
whereas several landscape parameters were. In suburbanizing areas, it is at least as important to consider landscape-scale
road density as to consider hydroperiod when designing conservation plans for these species. Furthermore, both isolated and
clustered pools provide these species important habitat and may require protection. Finally, the conceptual framework for
spotted-salamander management must be expanded so that spatial configuration at the landscape scale becomes a regular, integrated
component of conservation planning for this species. 相似文献