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1.
Measuring landscape configuration with normalized metrics 总被引：1，自引：1，他引：0
Natural and anthropogenic disturbances on natural landscapes reduce the abundance and alter the spatial arrangement of certain
habitat types. Measuring and modeling such alterations, and their biological effects, remains challenging in part because
many widely used configuration metrics are correlated with habitat amount. In this paper, we consider the sources of such
correlation, and distinguish process or sample-based correlation from functional correlation that may be an artifact of the
metrics themselves. Process correlation is not necessarily a serious problem for statistical inference, but functional correlation
would be. We propose that functional correlation may be reduced by normalizing metrics by habitat abundance. We illustrate
with normalized versions of total core area, mean nearest neighbor distance, and mean shape index, and show informally that
the standard versions of these metrics should exhibit functional correlation. We evaluate the normalized metrics on samples
of harvested and undisturbed forested landscapes, and on simulated landscapes generated with varying degrees of spatial autocorrelation.
Normalization markedly reduced correlations with habitat abundance on natural landscapes, but not on simulated landscapes.
The reasons for this appear to be a combination of differing variances in metric values within levels of habitat abundance,
and of the precise form of the relationships between habitat abundance and the un-normalized metrics. In all cases, the normalization
changes the ordering of landscapes by metric values across levels of habitat abundance. In consequence, normalized and standard
metrics cannot both be accurate measures of configuration. We conclude that statistical modeling of ecological response data
is needed to finally determine the merits of the normalizations. 相似文献
2.
Habitat configuration has important implications for the persistence of faunal and floral populations at a variety of spatial
scales. Forest harvesting alters habitat configurations. However, measuring and predicting such alterations remains challenging,
in part because previously developed metrics of habitat configuration are often not statistically independent of habitat amount.
Thus, their ability to measure independent effects of habitat configurations and habitat amount on ecosystem components such
as wildlife populations has been limited. Here, we evaluate habitat configuration based on newly developed metrics that are
independent of habitat amount but do not depend on regression residuals of abundance and configuration relationships on any
population of landscapes. We use these new metrics to measure and predict changes in habitat configuration following forest
harvesting in the boreal forest of Alberta, Canada. Our findings clearly demonstrate changes in habitat configuration resulting
from forest harvesting can be predicted precisely with information about initial habitat patch structure and harvesting patterns.
Because forest harvesting has significant implications for habitat configuration, accurately predicting these changes is critical
for determining if forest harvesting strategies are sustainable for ecosystem components and processes. This study provides
a set of novel, robust metrics for tracking landscape-scale changes in habitat configuration in harvested boreal forests. 相似文献
3.
Víctor Arroyo-Rodríguez Iraida M. González-Perez Adriana Garmendia Mireia Solà Alejandro Estrada 《Landscape Ecology》2013,28(9):1717-1727
Land-use change is forcing many animal populations to inhabit forest patches in which different processes can threaten their survival. Some threatening processes are mainly related to forest patch characteristics, but others depend principally on the landscape spatial context. Thus, the impact of both patch and landscape spatial attributes needs to be assessed to have a better understanding of the habitat spatial attributes that constraint the maintenance of populations in fragmented landscapes. Here, we evaluated the relative effect of three patch-scale (i.e., patch size, shape, and isolation) and five landscape-scale metrics (i.e., forest cover, fragmentation, edge density, mean inter-patch isolation distance, and matrix permeability) on population composition and structure of black howler monkeys (Alouatta pigra) in the Lacandona rainforest, Mexico. We measured the landscape-scale metrics at two spatial scales: within 100 and 500 ha landscapes. Our findings revealed that howler monkeys were more strongly affected by local-scale metrics. Smaller and more isolated forest patches showed a lower number of individuals but at higher densities. Population density also tended to be positively associated to matrices with higher proportion of secondary forests and arboreal crops (i.e. with greater permeability), most probably because these matrices can offer supplementary foods. The immature-to-female ratio also increased with matrix permeability, shape complexity, and edge density; habitat characteristics that can increase landscape connectivity and sources availability. The prevention of habitat loss and isolation, and the increment of matrix permeability are therefore needed for the conservation of this endangered Neotropical mammal. 相似文献
4.
Besides providing habitat to the grizzly bear (Ursus arctos) and other wildlife, the Rocky Mountain foothills of Alberta, Canada hosts considerable mining, seismic oil and gas exploration
and production, and forest harvesting activities. Worldwide, such human activities influence the configuration and composition
of the landscape. We assessed seismic cutline effects on landscape structure and grizzly bear use during early summer of 1999
and 2000. We studied five female and two male bears, which were GPS-collared in the spring following den emergence. The area
available to this population was stratified into 49 km2 hexagon-shaped sub-landscapes. The scale of this stratification was determined by patterns of bear movement. Fourteen compositional
and configurational landscape metrics were calculated within each landscape unit, and bear use points were pooled or ‘binned’
within each unit. Landscape use was related to landscape metrics using a Generalized Linear Model (GLM). We found that seismic
cutline proportion did not explain landscape use by grizzly bears; however secondary effects of cutlines on landscape structure
did. Declining use was mainly associated with increasing proportions of closed forest, and increasing variation of inter-patch
distances, while use was mainly increasing with increasing mean patch size. An earlier investigation had demonstrated that
adding seismic cutlines to grizzly bear habitat caused increases in the variation of inter-patch distances. Since the landscape
structure of this grizzly bear population will continue to change as a function of increased levels of resource extraction
activities in the near future, it is crucial to further study the detailed meaning of landscape structure at the large and
small scale for effective conservation efforts. 相似文献
5.
Forest managers in Canada need to model landscape pattern or spatial configurationoverlarge (100,000 km2) regions. This presents a scalingproblem, as landscape configuration is measured at a high spatial resolution,but a low spatial resolution is indicated for regional simulation. We present astatistical solution to this scaling problem by showing how a wide range oflandscape pattern metrics can be modelled from low resolution data. Our studyarea comprises about 75,000 km2 of boreal mixedwoodforest in northeast Alberta, Canada. Within this area we gridded a sample of 84digital forest cover maps, each about 9500 ha in size, to aresolution of 1 ha and used FRAGSTATS to compute a suite oflandscape pattern metrics for each map. We then used multivariate dimensionreduction techniques and canonical correlation analysis to model therelationship between landscape pattern metrics and simpler stand table metricsthat are easily obtained from non-spatial forest inventories. These analyseswere performed on four habitat types common in boreal mixedwood forests: youngdeciduous, old deciduous, white spruce, and mixedwood types. Using only threelandscape variables obtained directly from stand attribute tables (totalhabitatarea, and the mean and standard deviation of habitat patch size), ourstatistical models explained more than 73% of the joint variation in fivelandscape pattern metrics (representing patch shape, forest interior habitat,and patch isolation). By PCA, these five indices captured much of the totalvariability in the rich set of landscape pattern metrics that FRAGSTATS cangenerate. The predictor variables and strengths of association were highlyconsistent across habitat classes. We illustrate the potential use of suchstatistical relationships by simulating the regional, cumulative effects ofwildfire and forest management on the spatial arrangement of forest patches,using non-spatial stand attribute tables.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
6.
We present an approach that allows current, retrospective and future relative abundances of mammal species to be predicted
across landscapes. A spatial generalized regression model of species relative abundance based on habitat quality and time
since disturbance was combined with coverages of the spatial distribution of habitat quality derived from a simulation model
which predicts the historical and future spatial arrangement of forest habitat. The strength of this approach is that the
input habitat data can be derived as part of a standard forest inventory mapping program with the addition of high spatial
resolution remote sensing imagery. Furthermore, it operates at the scale used for wildlife management in Australia, which
makes it widely applicable. To demonstrate the approach we use data collected over 20 years on the long-nosed potoroo (Potorous tridactylus) and the large wallabies (red-necked wallaby, Macropus rufogriseus, and swamp wallaby, Wallabia bicolor) and their habitats following wildfire. Results indicate the relative abundance of the potoroo has increased, from initially
sparse numbers of less than 0.5 % of plot-night occurrences to close to 3% approximately twenty years after a major fire event.
The large wallabies by contrast decreased in relative abundance from about 20% since the major fire event. Presently the relative
abundance of large wallabies was modelled at 2% of plot-nights with tracks which was very low. Predictions of future relative
abundance without additional disturbance were low, with the region likely to be unsuitable for the species in the next 5 years.
These models offer tools for investigating the current and historical abundances of key species which can provide data to
forest managers for wildlife management thereby translating current scientific understanding into tools suitable for every-day
use by forest managers.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Jones Gavin M. Kramer H. Anu Whitmore Sheila A. Berigan William J. Tempel Douglas J. Wood Connor M. Hobart Brendan K. Erker Tedward Atuo Fidelis A. Pietrunti Nicole F. Kelsey Rodd Gutiérrez R. J. Peery M. Zachariah 《Landscape Ecology》2020,35(5):1199-1213
Context
Climate and land-use change have led to disturbance regimes in many ecosystems without a historical analog, leading to uncertainty about how species adapted to past conditions will respond to novel post-disturbance landscapes.
ObjectivesWe examined habitat selection by spotted owls in a post-fire landscape. We tested whether selection or avoidance of severely burned areas could be explained by patch size or configuration, and whether variation in selection among individuals could be explained by differences in habitat availability.
MethodsWe applied mixed-effects models to GPS data from 20 spotted owls in the Sierra Nevada, California, USA, with individual owls occupying home ranges spanning a broad range of post-fire conditions after the 2014 King Fire.
ResultsIndividual spotted owls whose home ranges experienced less severe fire (<?5% of home range severely burned) tended to select severely burned forest, but owls avoided severely burned forest when more of their home range was affected (~ 5–40%). Owls also tended to select severe fire patches that were smaller in size and more complex in shape, and rarely traveled?>?100-m into severe fire patches. Spotted owls avoided areas that had experienced post-fire salvage logging but the interpretation of this effect was nuanced. Owls also avoided areas that were classified as open and/or young forest prior to the fire.
ConclusionsOur results support the hypothesis that spotted owls are adapted to historical fire regimes characterized by small severe fire patches in this region. Shifts in disturbance regimes that produce novel landscape patterns characterized by large, homogeneous patches of high-severity fire may negatively affect this species.
相似文献8.
Fire is an important natural disturbance in the Mediterranean-climate coastal shrublands of southern California. However,
anthropogenic ignitions have increased fire frequency to the point that it threatens the persistence of some shrub species
and favors the expansion of exotic annual grasses. Because human settlement is a primary driver of increased ignitions, we
integrated a landscape model of disturbance and succession (LANDIS) with an urban growth model (UGM) to simulate the combined
effects of urban development and high fire frequency on the distribution of coastal shrublands. We tested whether urban development
would contribute to an expansion of the wildland-urban interface (WUI) and/or change in average fire return intervals and
compared the relative impacts of direct habitat loss and altered fire regimes on functional vegetation types. We also evaluated
two methods of integrating the simulation models. The development pattern predicted by the UGM was predominantly aggregated,
which minimized the expansion of the WUI and increase in fire frequency, suggesting that fire risk may be higher at intermediate
levels of urbanization due to the spatial arrangement of ignition sources and fuel. The comparison of model coupling methods
illustrated how cumulative effects of repeated fires may occur gradually as urban development expands across the landscape.
Coastal sage scrub species and resprouting chaparral were more susceptible to direct habitat loss, but increased fire frequency
was more of a concern to obligate seeder species that germinate from a persistent seed bank. Simulating different scenarios
of fire frequency and urban growth within one modeling framework can help managers locate areas of highest risk and determine
which vegetation types are most vulnerable to direct habitat loss, altered fire regimes, or both. 相似文献
9.
Context
Methods quantifying habitat patch importance for maintaining habitat network connectivity have been emphasized in helping to prioritize conservation actions. Functional connectivity is accepted as depending on landscape resistance, and several measures of functional inter-patch distance have been designed. However, how the inter-patch distance, i.e., based on least-cost path or multiple paths, influences the identification of key habitat patches has not been explored.Objectives
We compared the prioritization of habitat patches according to least-cost distance (LCD) and resistance distance (RD), using common binary and probabilistic connectivity metrics.Methods
Our comparison was based on a generic functional group of forest mammals with different dispersal distances, and was applied to two landscapes differing in their spatial extent and fragmentation level.Results
We found that habitat patch prioritization did not depend on distance type when considering the role of patch as contributing to dispersal fluxes. However, the role of patch as a connector facilitating dispersal might be overestimated by LCD-based indices compared with RD for short- and medium-distance dispersal. In particular, when prioritization was based on dispersal probability, the consideration of alternatives routes identified the connectors that probably provided functional connectivity for species in the long term. However, the use of LCD might help identify landscape areas that need critical restoration to improve individual dispersal.Conclusions
Our results provide new insights about the way that inter-patch distance is viewed changes the evaluation of functional connectivity. Accordingly, prioritization methods should be carefully selected according to assumptions about population functioning and conservation aims.10.
Ricardo Rocha Milou Groenenberg Paulo E. D. Bobrowiec Mar Cabeza Jorge M. Palmeirim Christoph F. J. Meyer 《Landscape Ecology》2017,32(1):31-45
Context
Habitat loss, fragmentation and degradation are widespread drivers of biodiversity decline. Understanding how habitat quality interacts with landscape context, and how they jointly affect species in human-modified landscapes, is of great importance for informing conservation and management.Objectives
We used a whole-ecosystem manipulation experiment in the Brazilian Amazon to investigate the relative roles of local and landscape attributes in affecting bat assemblages at an interior-edge-matrix disturbance gradient.Methods
We surveyed bats in 39 sites, comprising continuous forest (CF), fragments, forest edges and intervening secondary regrowth. For each site, we assessed vegetation structure (local-scale variable) and, for five focal scales, quantified habitat amount and four landscape configuration metrics.Results
Smaller fragments, edges and regrowth sites had fewer species and higher levels of dominance than CF. Regardless of the landscape scale analysed, species richness and evenness were mostly related to the amount of forest cover. Vegetation structure and configurational metrics were important predictors of abundance, whereby the magnitude and direction of response to configurational metrics were scale-dependent. Responses were ensemble-specific with local-scale vegetation structure being more important for frugivorous than for gleaning animalivorous bats.Conclusions
Our study indicates that scale-sensitive measures of landscape structure are needed for a more comprehensive understanding of the effects of fragmentation on tropical biota. Although forest fragments and regrowth habitats can be of conservation significance for tropical bats our results further emphasize that primary forest is of irreplaceable value, underlining that their conservation can only be achieved by the preservation of large expanses of pristine habitat.11.
Robert M. Scheller Wayne D. Spencer Heather Rustigian-Romsos Alexandra D. Syphard Brendan C. Ward James R. Strittholt 《Landscape Ecology》2011,26(10):1491-1504
Natural resource managers are often challenged with balancing requirements to maintain wildlife populations and to reduce
risks of catastrophic or dangerous wildfires. This challenge is exemplified in the Sierra Nevada of California, where proposals
to thin vegetation to reduce wildfire risks have been highly controversial, in part because vegetation treatments could adversely
affect an imperiled population of the fisher (Martes pennanti) located in the southern Sierra Nevada. The fisher is an uncommon forest carnivore associated with the types of dense, structurally
complex forests often targeted for fuel reduction treatments. Vegetation thinning and removal of dead-wood structures would
reduce fisher habitat value and remove essential habitat elements used by fishers for resting and denning. However, crown-replacing
wildfires also threaten the population’s habitat, potentially over much broader areas than the treatments intended to reduce
wildfire risks. To investigate the potential relative risks of wildfires and fuels treatments on this isolated fisher population,
we coupled three spatial models to simulate the stochastic and interacting effects of wildfires and fuels management on fisher
habitat and population size: a spatially dynamic forest succession and disturbance model, a fisher habitat model, and a fisher
metapopulation model, which assumed that fisher fecundity and survivorship correlate with habitat quality. We systematically
varied fuel treatment rate, treatment intensity, and fire regime, and assessed their relative effects on the modeled fisher
population over 60 years. After estimating the number of adult female fishers remaining at the end of each simulation scenario,
we compared the immediate negative effects of fuel treatments to the longer-term positive effect of fuel treatment (via reduction
of fire hazard) using structural equation modeling. Our simulations suggest that the direct, negative effects of fuel treatments
on fisher population size are generally smaller than the indirect, positive effects of fuel treatments, because fuels treatments
reduced the probability of large wildfires that can damage and fragment habitat over larger areas. The benefits of fuel treatments
varied by elevation and treatment location with the highest net benefits to fisher found at higher elevations and within higher
quality fisher habitat. Simulated fire regime also had a large effect with the largest net benefit of fuel treatments occurring
when a more severe fire regime was simulated. However, there was large uncertainty in our projections due to stochastic spatial
and temporal wildfires dynamic and fisher population dynamics. Our results demonstrate the difficulty of projecting future
populations in systems characterized by large, infrequent, stochastic disturbances. Nevertheless, these coupled models offer
a useful decision-support system for evaluating the relative effects of alternative management scenarios; and uncertainties
can be reduced as additional data accumulate to refine and validate the models. 相似文献
12.
Cumulative effects of roads and logging on landscape structure in the San Juan Mountains,Colorado (USA) 总被引：11，自引：0，他引：11
In the southern Rocky Mountains of temperate North America, the effects of Euro-American activities on disturbance regimes and landscape patterns have been less ubiquitous and less straightforward in high-elevation landscapes than in low-elevation landscapes. Despite apparently little change in the natural disturbance regime, there is increasing concern that forest management activities related mainly to timber harvest and to the extensive network of roads constructed to support timber harvest, fire control, and recreation since the late 1800s have altered disturbance regimes and landscape structure. We investigated the magnitude of change in landscape structure resulting from roads and logging since the onset of timber harvest activities in 1950. We found limited evidence for significant impacts in our study area when all lands within the landscape were considered. The relatively minor changes we observed reflected the vast buffering capacity of the large proportion of lands managed for purposes other than timber (e.g., wilderness). Significant changes in landscape structure and fragmentation of mature forest were, however, evident on lands designated as suitable timberlands. Roughly half of the mature coniferous forest was converted to young stands; mean patch size and core area declined by 40% and 25%, respectively, and contrast-weighted edge density increased 2- to 3-fold. Overall, roads had a greater impact on landscape structure than logging in our study area. Indeed, the 3-fold increase in road density between 1950–1993 accounted for most of the changes in landscape configuration associated with mean patch size, edge density, and core area. The extent of area evaluated and the period over which change was evaluated had a large impact on the magnitude of change detected and our conclusions regarding the ecological significance of those changes. Specifically, the cumulative impact on landscape structure was negligible over a 10-year period, but was notable over a 40-year period. In addition, the magnitude of change in landscape structure between 1950–1993 varied as a function of landscape extent. At the scale of the 228000 ha landscape, change in landscape structure was trivial, suggesting that the landscape was capable of fully incorporating the disturbances with minimal impact. However, at intermediate scales of 1000–10000 ha landscapes, change in landscape structure was quite evident, suggesting that there may be an optimal range of scales for detecting changes in landscape structure within the study area. 相似文献
13.
Purpose
Wildfire spatial patterns drive ecological processes including vegetation succession and wildlife community dynamics. Such patterns may be changing due to fire suppression policies and climate change, making characterization of trends in post-fire mosaics important for understanding and managing fire-prone ecosystems.Methods
For wildfires in California’s yellow pine and mixed-conifer forests, spatial pattern trends of two components of the post-fire severity matrix were assessed for 1984–2015: (1) unchanged or very low-severity and (2) high-severity, which represent remnant forest and stand-replacing fire, respectively. Trends were evaluated for metrics of total and proportional burned area, shape complexity, aggregation, and core area. Additionally, comparisons were made between management units where fire suppression is commonly practiced and those with a history of managing wildfire for ecological/resource benefits.Results
Unchanged or very low-severity area per fire decreased proportionally through time, and became increasingly fragmented. High-severity area and core area increased on average across most of California, with the high-severity component also becoming simpler in shape in the Sierra Nevada. Compared to suppression units, managed wildfire units lack an increase in high-severity area, have less aggregated post-fire mosaics, and more high-severity spatial complexity.Conclusions
Documented changes in severity patterns have cascading ecological effects including increased vegetation type conversion risk, habitat availability shifts, and remnant forest fragmentation. These changes likely benefit early-seral-associated species at the expense of mature closed-canopy forest-associated species. Managed wildfire appears to moderate some effects of fire suppression, and may help buy time for ecosystems and managers to respond to a changing climate.14.
Simulating the cumulative effects of multiple forest management strategies on landscape measures of forest sustainability 总被引：1，自引：2，他引：1
While the cumulative effects of the actions of multiple owners have long been recognized as critically relevant to efforts
to maintain sustainable forests at the landscape scale, few studies have addressed these effects. We used the HARVEST timber
harvest simulator to predict the cumulative effects of four owner groups (two paper companies, a state forest and non-industrial
private owners) with different management objectives on landscape pattern in an upper Michigan landscape managed primarily
for timber production. We quantified trends in landscape pattern metrics that were linked to Montreal Process indicators of
forest sustainability, and used a simple wildlife habitat model to project habitat trends. Our results showed that most trends
were considered favorable for forest sustainability, but that some were not. The proportion of all age classes and some forest
types moved closer to presettlement conditions. The trend for the size of uneven-aged patches was essentially flat while the
average size of patches of the oldest and youngest age classes increased and the size of patches of the remaining age classes
decreased. Forest fragmentation generally declined, but edge density of age classes increased. Late seral forest habitat increased
while early successional habitat declined. The owners use different management systems that cumulatively produce a diversity
of habitats. Our approach provides a tool to evaluate such cumulative effects on other landscapes owned by multiple owners.
The approach holds promise for helping landowner groups develop and evaluate cooperative strategies to improve landscape patterns
for forest sustainability. 相似文献
15.
Piotr Nowicki Vladimir Vrabec Birgit Binzenhöfer Johann Feil Barbara Zakšek Thomas Hovestadt Josef Settele 《Landscape Ecology》2014,29(3):401-412
Metapopulation models typically assume that suitable habitats occupied by local populations and unsuitable matrix separating them form a ‘black-and-white’ landscape mosaic, in which dispersal is primarily determined by the spatial configuration of habitat patches. In reality, however, the matrix composition is also likely to influence dispersal. Using intensive mark-recapture surveys we investigated inter-patch movements in Maculinea (Phengaris) nausithous and M. teleius occurring sympatrically in six metapopulations. Three of these metapopulations had the matrix dominated by forest, an inhospitable environment for grassland butterflies, whereas in the remaining three the matrix was mostly composed of open environments. Dispersal parameters derived with the Virtual Migration model revealed significant differences between both groups of metapopulations. Both species had a lower propensity to emigrate from their natal habitat patches, and they suffered substantially higher dispersal mortality in the metapopulations with forest matrix. On the other hand, mean dispersal distances were roughly an order of magnitude longer in forest matrix as compared with open landscapes (ca. 500–1,500 vs. 100–200 m). Our results suggest that inhospitable forest matrix induces strong selection against dispersal, leading to a reduced emigration rate. At the same time, the selection may promote emigrants with good dispersal abilities, which are able to perform long-distance movements. Thus, while it is generally believed that a matrix structurally similar to the habitat of a species should improve the functional connectivity of habitat patches, our findings imply that this may not necessarily be the case. 相似文献
16.
For some time, ecologists have known that spatial patterns of forest structure reflected disturbance and recovery history, disturbance severity and underlying influences of environmental gradients. In spite of this awareness, historical forest structure has been little used to expand knowledge of historical fire severity. Here, we used forest structure to predict pre-management era fire severity across three biogeoclimatic zones in eastern Washington State, USA, that contained extensive mixed conifer forests. We randomly selected 10% of the subwatersheds in each zone, delineated patch boundaries, and photo-interpreted the vegetation attributes of every patch in each subwatershed using the oldest available stereo-aerial photography. We statistically reconstructed the vegetation of any patch showing evidence of early selective harvesting, and then classified them as to their most recent fire severity. Classification used published percent canopy mortality definitions and a dichotomized procedure that considered the overstory and understory canopy cover and size class attributes of a patch, and the fire tolerance of its cover type. Mixed severity fires were most prevalent, regardless of forest type. The structure of mixed conifer patches, in particular, was formed by a mix of disturbance severities. In moist mixed conifer, stand replacement effects were more widespread in patches than surface fire effects, while in dry mixed conifer, surface fire effects were more widespread by nearly 2:1. However, evidence for low severity fires as the primary influence, or of abundant old park-like patches, was lacking in both the dry and moist mixed conifer forests. The relatively low abundance of old, park-like or similar forest patches, high abundance of young and intermediate-aged patches, and widespread evidence of partial stand and stand-replacing fire suggested that variable fire severity and non-equilibrium patch dynamics were primarily at work. 相似文献
17.
Forest insects cause defoliation disturbances with complex spatial dynamics. These are difficult to measure but critical for models of disturbance risk that inform forest management. Understanding of spatial dynamics has lagged behind other disturbance processes because traditional defoliation sketch map data often suffered from inadequate precision or spatial resolution. We sought to clarify the influence of underlying habitat characteristics on outbreak patterns by combining forest plots, GIS data and defoliation intensity maps modeled from Landsat imagery. We quantified dependence of defoliation on spatial patterns of host abundance, phenology, topography, and pesticide spray for a recent gypsy moth outbreak (2000–2001), in a mixed deciduous forest in western Maryland, USA. We used semivariograms and hierarchical partitioning to quantify spatial patterns and variable importance. Habitat characteristics from plot data explained 21 % of defoliation variance in 2000 from tree density, phenological asynchrony, pesticide spray status, and landform index and 34 % of the variance in 2001 from previous-year defoliation, relative abundance of non-host species, phenological asynchrony, pesticide spray status, and relative slope position. Spatial autocorrelation in residual defoliation ranged over distances of 788 m in 2000 and 461 m in 2001, corresponding well with gypsy moth larval dispersal distances (100 m to 1 km). Un-measured processes such as predation, virus and pathogen occurrence likely contribute to unexplained variance. Because the spatial dynamics of these factors are largely unknown, our results support modeling gypsy moth defoliation as a function of dependence on significant exogenous characteristics and residual spatial pattern matching. 相似文献
18.
Habitat isolation can affect the distribution and abundance of wildlife, but it is an ambiguous attribute to measure. Presumably, isolation is a characteristic of a habitat patch that reflects how spatially inaccessible it is to dispersing organisms. We identified four isolation metrics (nearest-neighbor distance, Voronoi polygons, proximity index, and habitat buffers) that were representative of the different families of metrics that are commonly used in the literature to measure patch isolation. Using simulated data, we evaluated the ability of each isolation metric to predict animal dispersal. We examined the simulated movement of organisms in two types of landscapes: an artificially-generated point-pattern landscapes where patch size and shape were consistent and only the arrangement of patches varied, and realistic landscapes derived from a geographic information system (GIS) of forest-vegetation maps where patch size, shape, and isolation were variable. We tested the performance of the four isolation metrics by examining the strength of the correlation between observed immigration rate in the simulations and each patch isolation metric. We also evaluated whether each isolation metric would perform consistently under varying conditions of patch size/shape, total amount of habitat in the landscape, and proximity of the patch to the landscape edge. The results indicate that a commonly-used distance-based metric, nearest-neighbor distance, did not adequately predict immigration rate when patch size and shape were variable. Area-informed isolation metrics, such as the amount of available habitat within a given radius of a patch, were most successful at predicting immigration. Overall, the use of area-informed metrics is advocated despite the limitation that these metrics require parameterization to reflect the movement capacity of the organism studied.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
19.
Loss of connectivity is one of the main causes of decreases in habitat availability and, thus, in species abundance and occurrence
in fragmented landscapes. It is therefore important to measure habitat connectivity for conservation purposes, but there are
several difficulties in quantifying connectivity, including the need for species movement behavioral data and the existence
of few consistent indices to describe such data. In the present study, we used a graph theoretical framework to measure habitat
availability, and we evaluate whether this variable is adequate to explain the occurrence pattern of an Atlantic rainforest
bird (Pyriglena leucoptera, Thamnophilidae). The playback technique was used to parameterize the connectivity component of habitat availability indices
and to determine the presence or absence of the study species in forest patches. Patch- and landscape-level habitat availability
indices were considered as explanatory variables. Two of these were landscape-level indices, which varied in terms of how
inter-patch connections are defined, using either a binary or probabilistic approach. This study produced four striking results.
First, even short open gaps may disrupt habitat continuity for P. leucoptera. Second, the occurrence of P. leucoptera was positively affected by habitat availability. Third, proper measures of this explanatory variable should account for the
landscape context around the focal patch, emphasizing the importance of habitat connectivity. Finally, habitat availability
indices should consider probabilistic and not binary inter-patch connections when intending to explain the occurrence of bird
species in fragmented landscapes. We discuss some conservation implications of our results, stressing the advantages of an
ecologically scaled graph theoretical framework. 相似文献
20.
Repeated sequences of digitised and geo-referenced historical aerial photography provide a powerful means of understanding
landscape change. We use this method to demonstrate a landscape wide expansion of closed forest (42% increase in total coverage)
in the Australian monsoon tropics over the past five decades. Retrospective habitat suitability models (HSI) of closed forest
derived using four landscape measures (drainage distance, slope angle, aspect and elevation) for imagery taken in 1947 correctly
forecast the subsequent spatial distribution of the expansion, with topographic fire protection primarily determining the
closed-forest distribution. The dynamics of the closed forest-savanna boundary were predicted accurately by generalised linear
models, with closed-forest expansion in fire-protected sites along forest edges and regression in the more fire-prone areas.
Two factors may plausibly explain the expansion of closed forests. First, eco-ethnographic records stress the skilful use
of fire by Aboriginal people in protecting isolated and locally resource-rich closed-forest patches. Second, the recent global
increase in atmospheric CO2 may be changing the competitive balance between savanna and forest by enabling C3 trees to grow fast enough to escape the fire trap presented by flammable C4 grasses. 相似文献