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1.
Behavior of class-level landscape metrics across gradients of class aggregation and area 总被引：4，自引：3，他引：4
Habitat loss and fragmentation processes strongly affect biodiversity conservation in landscapes undergoing anthropogenic land use changes. Many attempts have been made to use landscape structure metrics to quantify the independent and joint effects of these processes. Unfortunately, ecological interpretation of those metrics has been plagued by lack of thorough understanding of their theoretical behavior. We explored behavior of 50 metrics in neutral landscapes across a 21-step gradient in aggregation and a 19-step gradient in area using a full factorial design with 100 replicates of each of the 399 combinations of the two factors to assess how well metrics reflected changes in landscape structure. Metric values from real landscapes were used to determine the extent of neutral landscape space that is represented in real landscapes. We grouped metrics into three major behavioral classes: strongly related to focal class area (n=15), strongly related to aggregation (n=7), and jointly responding to area and aggregation (n=28). Metrics strongly related to class area exhibited a variety of distinct behaviors, and many of these metrics have unique interpretations that make each of them particularly useful in certain applications. Metrics strongly related to aggregation, independent of class area, are particularly useful in assessing effects of fragmentation. Moreover, metrics in this group exhibited a range of specific behaviors, highlighting subtle but different aspects of landscape aggregation even though we controlled only one aspect of aggregation. The non-linear behavior exhibited by many metrics renders interpretation difficult and use of linear analytical techniques inappropriate under many circumstances. Ultimately, comprehensive characterization of landscapes undergoing habitat loss and fragmentation will require using several metrics distributed across behavioral groups.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
2.
Can landscape indices predict ecological processes consistently? 总被引：36，自引：0，他引：36
The ecological interpretation of landscape patterns is one of the major objectives in landscape ecology. Both landscape patterns and ecological processes need to be quantified before statistical relationships between these variables can be examined. Landscape indices provide quantitative information about landscape pattern. Response variables or process rates quantify the outcome of ecological processes (e.g., dispersal success for landscape connectivity or Morisita's index for the spatial distribution of individuals). While the principal potential of this approach has been demonstrated in several studies, the robustness of the statistical relationships against variations in landscape structure or against variations of the ecological process itself has never been explicitly investigated. This paper investigates the consistency of correlations between a set of landscape indices (calculated with Fragstats) and three response variables from a simulated dispersal process across heterogeneous landscapes (cell immigration, dispersal success and search time) against variation in three experimental treatments (control variables): habitat amount, habitat fragmentation and dispersal behavior. I found strong correlations between some landscape indices and all three response variables. However, 68% of the statistical relationships were highly inconsistent and sometimes ambiguous for different landscape structures and for differences in dispersal behavior. Correlations between one landscape index and one response variable could range from highly positive to highly negative when derived from different spatial patterns. I furthermore compared correlation coefficients obtained from artificially generated (neutral) landscape models with those obtained from Landsat TM images. Both landscape representations produced equally strong and weak statistical relationships between landscape indices and response variables. This result supports the use of neutral landscape models in theoretical analyses of pattern-process relationships. 相似文献
3.
Pattern in ecological landscapes is often the result of different processes operating at different scales. Neutral landscape models were introduced in landscape ecology to differentiate patterns that are the result of simple random processes from patterns that arise from more complex ecological processes. Recent studies have used increasingly complex neutral models that incorporate contagion and other constraints on random patterns, as well as using neutral landscapes as input to spatial simulation models. Here, I consider a common mathematical framework based on spectral transforms that represents all neutral landscape models in terms of sets of spectral basis functions. Fractal and multi-fractal models are considered, as well as models with multiple scaling regions and anisotropy. All of the models considered are shown to be variations on a basic theme: a scaling relation between frequency and amplitude of spectral components. Two example landscapes examined showed long-range correlations (distances up to 1000 km) consistent with fractal scaling. 相似文献
4.
Increasing land ownership fragmentation in the United States is causing concerns with respect to its ecological implications
for forested landscapes. This is especially relevant given that human influence is one of the most significant driving forces
affecting the forest landscape. A method for generating realistic land ownership maps is needed to evaluate the effects of
ownership fragmentation on forest landscapes in combination with other natural processes captured in forest process models.
Ownership patterns from human activities usually generate landscape boundary shapes different from those arising from natural
processes. Spatial characteristics among ownership types – e.g., private, public ownership – may also differ. To address these
issues, we developed the Fragmented Land Ownership Spatial Simulator (FLOSS) to generate ownership patterns that reflect the
Public Land Survey System (PLSS) shapes and various patch size distributions among different types of ownership (e.g., private,
public). To evaluate FLOSS performance, we compared the simulated patterns with various ownership fragmentation levels to
the actual ownership patterns in the Missouri Ozarks by using selected landscape indices. FLOSS generated landscapes with
spatial characteristics similar to actual landscapes, suggesting that it can simulate different levels of ownership fragmentation.
This will allow FLOSS to serve as a feasible tool for evaluating forest management applications by spatially allocating various
management scenarios in a realistic way. The potentials and limitations of FLOSS application are discussed. 相似文献
5.
Road Density and Landscape Pattern in Relation to Housing Density,and Ownership,Land Cover,and Soils 总被引：5，自引：0，他引：5
Roads are conspicuous components of landscapes and play a substantial role in defining landscape pattern. Previous studies
have demonstrated the link between roads and their effects on ecological processes and landscape patterns. Less understood
is the placement of roads, and hence the patterns imposed by roads on the landscape in relation to factors describing land
use, land cover, and environmental heterogeneity. Our hypothesis was that variation in road density and landscape patterns
created by roads can be explained in relation to variables describing land use, land cover, and environmental factors. We
examined both road density and landscape patterns created by roads in relation to suitability of soil substrate as road subgrade,
land cover, lake area and perimeter, land ownership, and housing density across 19 predominantly forested counties in northern
Wisconsin, USA. Generalized least squares regression models showed that housing density and soils with excellent suitability
for road subgrade were positively related to road density while wetland area was negatively related. These relationships were
consistent across models for different road types. Landscape indices showed greater fragmentation by roads in areas with higher
housing density, and agriculture, grassland, and coniferous forest area, but less fragmentation with higher deciduous forest,
mixed forest, wetland, and lake area. These relationships provide insight into the complex relationships among social, institutional,
and environmental factors that influence where roads occur on the landscape. Our results are important for understanding the
impacts of roads on ecosystems and planning for their protection in the face of continued development. 相似文献
6.
Brian R. Miranda Brian R. Sturtevant Jian Yang Eric J. Gustafson 《Landscape Ecology》2009,24(5):587-598
We demonstrate a method to evaluate the degree to which a meta-model approximates spatial disturbance processes represented
by a more detailed model across a range of landscape conditions, using neutral landscapes and equivalence testing. We illustrate
this approach by comparing burn patterns produced by a relatively simple fire spread algorithm with those generated by a more
detailed fire behavior model from which the simpler algorithm was derived. Equivalence testing allows objective comparisons
of the output of simple and complex models, to determine if the results are significantly similar. Neutral landscape models
represent a range of landscape conditions that the model may encounter, allowing evaluation of the sensitivity and behavior
of the model to different landscape compositions and configurations. We first tested the model for universal applicability,
then narrowed the testing to assess the practical domain of applicability. As a whole, the calibrated simple model passed
the test for significant equivalence using the 25% threshold. When applied to a range of landscape conditions different from
the calibration scenarios, the model failed the tests for equivalence. Although our particular model failed the tests, the
neutral landscape models were helpful in determining an appropriate domain of applicability and in assessing the model sensitivity
to landscape changes. Equivalence testing provides an effective method for model comparison, and coupled with neutral landscapes,
our approach provides an objective way to assess the domain of applicability of a spatial model. 相似文献
7.
Habitat fragmentation is expected to disrupt dispersal, and thus we explored how patch metrics of landscape structure, such as percolation thresholds used to define landscape connectivity, corresponded with dispersal success on neutral landscapes. We simulated dispersal as either a purely random process (random direction and random step lengths) or as an area-limited random walk (random direction, but movement limited to an adjacent cell at each dispersal step) and quantified dispersal success for 1000 individuals on random and fractal landscape maps across a range of habitat abundance and fragmentation. Dispersal success increased with the number of cells a disperser could search (m), but poor dispersers (m<5) searching via area-limited dispersal on fractal landscapes were more successful at locating suitable habitat than random dispersers on either random or fractal landscapes. Dispersal success was enhanced on fractal landscapes relative to random ones because of the greater spatial contagion of habitat. Dispersal success decreased proportionate to habitat loss for poor dispersers (m=1) on random landscapes, but exhibited an abrupt threshold at low levels of habitat abundance (p<0.1) for area-limited dispersers (m<10) on fractal landscapes. Conventional metrics of patch structure, including percolation, did not exhibit threshold behavior in the region of the dispersal threshold. A lacunarity analysis of the gap structure of landscape patterns, however, revealed a strong threshold in the variability of gap sizes at low levels of habitat abundance (p<0.1) in fractal landscapes, the same region in which abrupt declines in dispersal success were observed. The interpatch distances or gaps across which dispersers must move in search of suitable habitat should influence dispersal success, and our results suggest that there is a critical gap-size structure to fractal landscapes that interferes with the ability of dispersers to locate suitable habitat when habitat is rare. We suggest that the gap structure of landscapes is a more important determinant of dispersal than patch structure, although both are ultimately required to predict the ecological consequences of habitat fragmentation. 相似文献
8.
Jenica M. Allen Thomas J. Leininger James D. Hurd Jr. Daniel L. Civco Alan E. Gelfand John A. Silander Jr. 《Landscape Ecology》2013,28(9):1671-1686
Woody invasive plants are an increasing component of the New England flora. Their success and geographic spread are mediated in part by landscape characteristics. We tested whether woody invasive plant richness was higher in landscapes with many forest edges relative to other forest types and explained land use/land cover and forest fragmentation patterns using socioeconomic and physical variables. Our models demonstrated that woody invasive plant richness was higher in landscapes with more edge forest relative to patch, perforated, and especially core forest types. Using spatially-explicit, hierarchical Bayesian, compositional data models we showed that infrastructure and physical factors, including road length and elevation range, and time-lagged socioeconomic factors, primarily population, help to explain development and forest fragmentation patterns. Our social–ecological approach identified landscape patterns driven by human development and linked them to increased woody plant invasions. Identifying these landscape patterns will aid ongoing efforts to use current distribution patterns to better predict where invasive species may occur in unsampled regions under current and future conditions. 相似文献
9.
Spatial and temporal analysis of landscape patterns 总被引：89，自引：0，他引：89
Monica G. Turner 《Landscape Ecology》1990,4(1):21-30
A variety of ecological questions now require the study of large regions and the understanding of spatial heterogeneity. Methods
for spatial-temporal analyses are becoming increasingly important for ecological studies. A grid cell based spatial analysis
program (SPAN) is described and results of landscape pattern analysis using SPAN are presentedd. Several ecological topics
in which geographic information systems (GIS) can play an important role (landscape pattern analysis, neutral models of pattern
and process, and extrapolation across spatial scales) are reviewed. To study the relationship between observed landscape patterns
and ecological processes, a neutral model approach is recommended. For example, the expected pattern (i.e., neutral model) of the spread of disturbance across a landscape can be generated and then tested using actual landscape data
that are stored in a GIS. Observed spatial or temporal patterns in ecological data may also be influenced by scale. Creating
a spatial data base frequently requires integrating data at different scales. Spatial is shown to influence landscape pattern
analyses, but extrapolation of data across spatial scales may be possible if the grain and extent of the data are specified.
The continued development and testing of new methods for spatial-temporal analysis will contribute to a general understanding
of landscape dynamics. 相似文献
10.
Michael C. Wimberly 《Landscape Ecology》2006,21(1):35-46
Although landscape ecology emphasizes the effects of spatial pattern on ecological processes, most neutral models of species–habitat relationships have treated habitat as a static constraint. Do the working hypotheses derived from these models extend to real landscapes where disturbances create a shifting mosaic? A spatial landscape simulator incorporating vegetation dynamics and a metapopulation model was used to compare species in static and dynamic landscapes with identical habitat amounts and spatial patterns. The main drivers of vegetation dynamics were stand-replacing disturbances, followed by gradual change from early-successional to old-growth habitats. Species dynamics were based on a simple occupancy model, with dispersal simulated as a random walk. As the proportion of available habitat (p) decreased from 1.0, species occupancy generally declined more rapidly and reached extinction at higher habitat levels in dynamic than in static landscapes. However, habitat occupancy was sometimes actually higher in dynamic landscapes than in static landscapes with similar habitat amounts and patterns. This effect was most pronounced at intermediate amounts of habitat (p = 0.3?0.6) for mobile species that had high colonization rates, but were unable to cross non-habitat patches. Differences between static and dynamic landscapes were contingent upon the initial metapopulation size and the shapes of disturbances and the resulting habitat patterns. Overall, the results demonstrate that dispersal-limited species exhibit more pronounced critical behavior in dynamic landscapes than is predicted by simple neutral models based on static landscapes. Thus, caution should be exercised in extending generalizations derived from static landscape models to disturbance-driven landscape mosaics. 相似文献
11.
Stochastic generating models for simulating hierarchically structured multi-cover landscapes 总被引：3，自引：0，他引：3
For simulating hierarchically structured raster maps of landscapes that consist of multiple land cover types, we extend the concept of neutral landscape models to provide a general Markovian model. A stochastic transition matrix provides the probability rules that govern landscape fragmentation processes by assigning finer resolution land cover categories, given coarser resolution categories. This matrix can either be changed or remain the same at different resolutions. The probability rules may be defined for simulating properties of an actual landscape or they may be specified in a truly neutral manner to evaluate the effects of particular transition probability rules.For illustration, model parameters are defined heuristically to simulate properites of actual watershed-delineated landscapes in Pennsylvania. Three landscapes were chosen; one is mostly forested, one is in a transitional state between mostly forested and a mixture of agriculture, urban and suburban land, while the third is fully developed with only remnant forest patches that are small and disconnected. For each landscape type, a small sample of raster maps are simulated in a Monte Carlo fashion to illustrate how an empirical distribution of landscape measurements can be obtained. 相似文献
12.
Landscape metric scalograms (the response curves of landscape metrics to changing grain size) have been used to illustrate the scale effects of metrics for real landscapes. However, whether they detect the characteristic scale of hierarchically structured landscapes remains uncertain. To address this question, the scalograms of 26 class-level metrics were systematically examined for a simple random landscape, seven hierarchical neutral landscapes, and the real landscape of the Xilin River Basin of Inner Mongolia, China. The results show that when the fraction of the focal patch type (P) is below a critical value (P c), most metric scalograms are sensitive to change in single-scale and lower-level hierarchical structure and insensitive to change in higher-level hierarchical structure. The scalograms of only a few metrics measuring spatial aggregation and connectedness are sensitive to change in intermediate-level hierarchical structure. Most metric scalograms explicitly identify the characteristic scale of a single-scale landscape and fine or intermediate characteristic scales of a multi-scale landscape for both simulated and real landscapes. When P exceeds P c, only some metrics detect scale and change in structure. The scalograms of total class area and Euclidean nearest-neighbor distance cannot detect scale or change in structure in either case. Landscape metric scalograms are useful for addressing scale issues, including illustrating the scale effects of spatial patterns, detecting multi-scale patterns, and developing possible scaling relations.
相似文献13.
Previous research has suggested that ducks and songbirds may benefit from prairie landscapes that consist primarily of contiguous
grasslands. However, the relative importance of landscape-level vs. local characteristics on mechanisms underlying observed
patterns is unclear. We measured effects of grassland amount and fragmentation on upland and wetland songbird and duck density
and nest success, and on some nest predators, across 16 landscapes in southern Alberta, Canada. We compared these landscape-level
effects with local-scale responses, including distance to various edges and vegetation characteristics. We also evaluated
several statistical approaches to comparing effects of habitat characteristics at multiple spatial scales. Few species were
influenced by grassland amount or fragmentation. In contrast, distance to edge and local vegetation characteristics had significant
effects on densities and nest success of many species. Previous studies that reported effects of landscape characteristics
may have detected patterns driven by local mechanisms. As a corollary, results were very sensitive to statistical model structure;
landscape level effects were much less apparent when local characteristics were included in the models. 相似文献
14.
The behavior of landscape metrics commonly used in the study of habitat fragmentation 总被引：40，自引：2，他引：38
A meaningful interpretation of landscape metrics is possible only when the limitations of each measure are fully understood, the range of attainable values is known, and the user is aware of potential shifts in the range of values due to characteristics of landscape patches. To examine the behavior of landscape metrics, we generated artificial landscapes that mimicked fragmentation processes while controlling the size and shape of patches in the landscape and the mode of disturbance growth. We developed nine series of increasingly fragmented landscapes and used these to investigate the behavior of edge density, contagion, mean nearest neighbor distance, mean proximity index, perimeter-area fractal dimension, and mass fractal dimension. We found that most of the measures were highly correlated, especially contagion and edge density, which had a near-perfect inverse correspondence. Many of the measures were linearly-associated with increasing disturbance until the proportion of disturbance on the landscape was approximately 0.40, with non-linear associations at higher proportions. None of the measures was able to differentiate between landscape patterns characterized by dispersed versus aggregated patches. The highest attainable value of each measure was altered by either patch size or shape, and in some cases, by both attributes. We summarize our findings by discussing the utility of each metric. 相似文献
15.
A hierarchical neutral model for landscape analysis 总被引：11，自引：0，他引：11
Empirical studies have revealed scaled structure on a variety of landscapes. Understanding processes that produce these structures
requires neutral models with hierarchical structure. The present study presents a method for generating random maps possessing
a variety of hierarchical structures. The properties of these scaled landscapes are analyzed and compared to patterns on totally
random, unstructured landscapes. Hierar-chical structure permits percolation (i.e., continous habitat spanning the landscape) under a greater variety of conditions than found on totally random landscapes.
Habitat clusters on structured maps tend to have smaller perimeters. The clusters tend to be less clumped on sparsely occupied
landscapes and more clumped in densely occupied conditions. Hierarchical structure changes the expected spatial properties
of the landscape, indicating a strong need for this new generation of neutral models.
Research supported by the Ecological Research Division, Office to Health and Environmental Research, U.S. Department of Energy
under contract No. DE-AC05-840R21400 with Martin Marietta, Energy Systems, Inc. Environmental Sciences Publication No. 3813,
ORNL. 相似文献
16.
Climate, topography, fuel loadings, and human activities all affect spatial and temporal patterns of fire occurrence. Because
fire is modeled as a stochastic process, for which each fire history is only one realization, a simulation approach is necessary
to understand baseline variability, thereby identifying constraints, or forcing functions, that affect fire regimes. With
a suitable neutral model, characteristics of natural fire regimes estimated from fire history data can be compared to a “null
hypothesis”. We generated random landscapes of fire-scarred trees via a point process with sequential spatial inhibition.
Random ignition points, fire sizes, and fire years were drawn from uniform and exponential family probability distributions.
We compared two characteristics of neutral fire regimes to those from five watersheds in eastern Washington that have experienced
low-severity fire. Composite fire intervals (CFIs) at multiple spatial scales displayed similar monotonic decreases with increasing
sample area in neutral vs. real landscapes, although patterns of residuals from statistical models differed. In contrast,
parameters of the Weibull distribution associated with temporal trends in fire hazard exhibited different forms of scale dependence
in real vs. simulated data. Clear patterns in neutral landscapes suggest that deviations from them in empirical data represent
real constraints on fire regimes (e.g., topography, fuels). As with any null model, however, neutral fire-regime models need
to be carefully tuned to avoid confounding these constraints with artifacts of modeling. Neutral models show promise for investigating
low-severity fire regimes to separate intrinsic properties of stochastic processes from the effects of climate, fuel loadings,
topography, and management. 相似文献
17.
Connectivity measures: a review 总被引：8，自引：3，他引：5
One of the central problems in contemporary ecology and conservation biology is the drastic change of landscapes induced by
anthropogenic activities, resulting in habitat loss and fragmentation. For many wild living species, local extinctions of
fragmented populations are common and recolonization is critical for regional survival. Successful recolonization depends
on the availability of dispersing individuals and the degree of landscape connectivity. The obvious implications of landscape
connectivity for conservation biology have led to a proliferation of connectivity measures. However, general relationships
between landscape connectivity and landscape structure are lacking, and so are the relationships between different connectivity
metrics. Consequently, there is a need to develop landscape metrics that more accurately characterize the landscape with an
emphasis on the underlying processes. Here we review various definitions of landscape connectivity, explain their mathematical
connotations, and make some unifying conclusions and suggestions for future research. 相似文献
18.
Context
Quantitative grouping of similar landscape patterns is an important part of landscape ecology due to the relationship between a pattern and an underlying ecological process. One of the priorities in landscape ecology is a development of the theoretically consistent framework for quantifying, ordering and classifying landscape patterns.
ObjectiveTo demonstrate that the information theory as applied to a bivariate random variable provides a consistent framework for quantifying, ordering, and classifying landscape patterns.
MethodsAfter presenting information theory in the context of landscapes, information-theoretical metrics were calculated for an exemplar set of landscapes embodying all feasible configurations of land cover patterns. Sequences and 2D parametrization of patterns in this set were performed to demonstrate the feasibility of information theory for the analysis of landscape patterns.
ResultsUniversal classification of landscape into pattern configuration types was achieved by transforming landscapes into a 2D space of weakly correlated information-theoretical metrics. An ordering of landscapes by any single metric cannot produce a sequence of continuously changing patterns. In real-life patterns, diversity induces complexity—increasingly diverse patterns are increasingly complex.
ConclusionsInformation theory provides a consistent, theory-based framework for the analysis of landscape patterns. Information-theoretical parametrization of landscapes offers a method for their classification.
相似文献19.
Surface metrics: an alternative to patch metrics for the quantification of landscape structure 总被引：6，自引：3，他引：3
Modern landscape ecology is based on the patch mosaic paradigm, in which landscapes are conceptualized and analyzed as mosaics
of discrete patches. While this model has been widely successful, there are many situations where it is more meaningful to
model landscape structure based on continuous rather than discrete spatial heterogeneity. The growing field of surface metrology
offers a variety of surface metrics for quantifying landscape gradients, yet these metrics are largely unknown and/or unused
by landscape ecologists. In this paper, we describe a suite of surface metrics with potential for landscape ecological application.
We assessed the redundancy among metrics and sought to find groups of similarly behaved metrics by examining metric performance
across 264 sample landscapes in western Turkey. For comparative purposes and to evaluate the robustness of the observed patterns,
we examined 16 different patch mosaic models and 18 different landscape gradient models of landscape structure. Surface metrics
were highly redundant, but less so than patch metrics, and consistently aggregated into four cohesive clusters of similarly
behaved metrics representing surface roughness, shape of the surface height distribution, and angular and radial surface texture.
While the surface roughness metrics have strong analogs among the patch metrics, the other surface components are largely
unique to landscape gradients. We contend that the surface properties we identified are nearly universal and have potential
to offer new insights into landscape pattern–process relationships.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
20.