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Temporal change in fragmentation of continental US forests 总被引：1，自引：0，他引：1
James D. Wickham Kurt H. Riitters Timothy G. Wade Collin Homer 《Landscape Ecology》2008,23(8):891-898
Changes in forest ecosystem function and condition arise from changes in forest fragmentation. Previous studies estimated
forest fragmentation for the continental United States (US). In this study, new temporal land-cover data from the National
Land Cover Database (NLCD) were used to estimate changes in forest fragmentation at multiple scales for the continental US.
Early and late dates for the land-cover change data were ca. 1992 and ca. 2001. Forest density was used as a multi-scale index
of fragmentation by measuring the proportion of forest in neighborhoods ranging in size from 2.25 to 5314.41 ha. The multi-scale
forest density maps were classified using thresholds of 40% (patch), 60% (dominant), and 90% (interior) to analyze temporal
change of fragmentation. The loss of dominant and interior forest showed distinct scale effects, whereas loss of patch forest
was much less scale-dependent. Dominant forest loss doubled from the smallest to the largest spatial scale, while interior
forest loss increased by approximately 80% from the smallest to the second largest spatial scale, then decreased somewhat.
At the largest spatial scale, losses of dominant and interior forest were 5 and 10%, respectively, of their ca. 1992 amounts.
In contrast, patch forest loss increased by only 25% from the smallest to largest spatial scale. These results indicate that
continental US forests were sensitive to forest loss because of their already fragmented state. Forest loss would have had
to occur in an unlikely spatial pattern in order to avoid the proportionately greater impact on dominant and interior forest
at larger spatial scales. 相似文献
3.
Mapping Spatial Patterns with Morphological Image Processing 总被引：4，自引：3，他引：1
Peter Vogt Kurt H. Riitters Christine Estreguil Jacek Kozak Timothy G. Wade James D. Wickham 《Landscape Ecology》2007,22(2):171-177
We use morphological image processing for classifying spatial patterns at the pixel level on binary land-cover maps. Land-cover
pattern is classified as ‘perforated,’ ‘edge,’ ‘patch,’ and ‘core’ with higher spatial precision and thematic accuracy compared
to a previous approach based on image convolution, while retaining the capability to label these features at the pixel level
for any scale of observation. The implementation of morphological image processing is explained and then demonstrated, with
comparisons to results from image convolution, for a forest map of the Val Grande National Park in North Italy. 相似文献
4.
Context
Remote sensing has been a foundation of landscape ecology. The spatial resolution (pixel size) of remotely sensed land cover products has improved since the introduction of landscape ecology in the United States. Because patterns depend on spatial resolution, emerging improvements in the spatial resolution of land cover may lead to new insights about the scaling of landscape patterns.
ObjectiveWe compared forest fragmentation measures derived from very high resolution (1 m2) data with the same measures derived from the commonly used (30 m?×??30 m; 900 m2) Landsat-based data.
MethodsWe applied area-density scaling to binary (forest; non-forest) maps for both sources to derive source-specific estimates of dominant (density ≥?60%), interior (≥?90%), and intact (100%) forest.
ResultsSwitching from low- to high-resolution data produced statistical and geographic shifts in forest spatial patterns. Forest and non-forest features that were “invisible” at low resolution but identifiable at high resolution resulted in higher estimates of dominant and interior forest but lower estimates of intact forest from the high-resolution source. Overall, the high-resolution data detected more forest that was more contagiously distributed even at larger spatial scales.
ConclusionWe anticipate that improvements in the spatial resolution of remotely sensed land cover products will advance landscape ecology through re-interpretations of patterns and scaling, by fostering new landscape pattern measurements, and by testing new spatial pattern-ecological process hypotheses.
相似文献5.
Transitions in forest fragmentation: implications for restoration opportunities at regional scales 总被引：3，自引：0，他引：3
Wickham James D. Jones K. Bruce Riitters Kurt H. Wade Timothy G. O'Neill Robert V. 《Landscape Ecology》1999,14(2):137-145
Where the potential natural vegetation is continuous forest (e.g., eastern US), a region can be divided into smaller units (e.g., counties, watersheds), and a graph of the proportion of forest in the largest patch versus the proportion in anthropogenic cover can be used as an index of forest fragmentation. If forests are not fragmented beyond that converted to anthropogenic cover, there would be only one patch in the unit and its proportional size would equal 1 minus the percentage of anthropogenic cover. For a set of 130 watersheds in the mid-Atlantic region, there was a transition in forest fragmentation between 15 and 20% anthropogenic cover. The potential for mitigating fragmentation by connecting two or more disjunct forest patches was low when percent anthropogenic cover was low, highest at moderate proportions of anthropogenic cover, and again low as the proportion of anthropogenic cover increased toward 100%. This fragmentation index could be used to prioritize locations for restoration by targeting watersheds where there would be the greatest increase in the size of the largest forest patch. 相似文献
6.
A factor analysis of landscape pattern and structure metrics 总被引：92，自引：1，他引：91
K. H. Riitters R. V. O'Neill C. T. Hunsaker J. D. Wickham D. H. Yankee S. P. Timmins K. B. Jones B. L. Jackson 《Landscape Ecology》1995,10(1):23-39
Fifty-five metrics of landscape pattern and structure were calculated for 85 maps of land use and land cover. A multivariate factor analysis was used to identify the common axes (or dimensions) of pattern and structure which were measured by a reduced set of 26 metrics. The first six factors explained about 87% of the variation in the 26 landscape metrics. These factors were interpreted as composite measures of average patch compaction, overall image texture, average patch shape, patch perimeter-area scaling, number of attribute classes, and large-patch density-area scaling. We suggest that these factors can be represented in a simpler way by six univariate metrics - average perimeter-area ratio, contagion, standardized patch shape, patch perimeter-area scaling, number of attribute classes, and large-patch density-area scaling. 相似文献
7.
Predicting nutrient and sediment loadings to streams from landscape metrics: A multiple watershed study from the United States Mid-Atlantic Region 总被引：21，自引：1，他引：20
Jones K. Bruce Neale Anne C. Nash Maliha S. Van Remortel Rick D. Wickham James D. Riitters Kurt H. O'Neill Robert V. 《Landscape Ecology》2001,16(4):301-312
There has been an increasing interest in evaluating the relative condition or health of water resources at regional and national scales. Of particular interest is an ability to identify those areas where surface and ground waters have the greatest potential for high levels of nutrient and sediment loadings. High levels of nutrient and sediment loadings can have adverse effects on both humans and aquatic ecosystems. We analyzed the ability of landscape metrics generated from readily available, spatial data to predict nutrient and sediment yield to streams in the Mid-Atlantic Region in the United States. We used landscape metric coverages generated from a previous assessment of the entire Mid-Atlantic Region, and a set of stream sample data from the U.S. Geological Survey. Landscape metrics consistently explained high amounts of variation in nitrogen yields to streams (65 to 86% of the total variation). They also explained 73 and 79% of the variability in dissolved phosphorus and suspended sediment. Although there were differences in the nitrogen, phosphorus, and sediment models, the amount of agriculture, riparian forests, and atmospheric nitrate deposition (nitrogen only) consistently explained a high proportion of the variation in these models. Differences in the models also suggest potential differences in landscape-stream relationships between ecoregions or biophysical settings. The results of the study suggest that readily available, spatial data can be used to assess potential nutrient and sediment loadings to streams, but that it will be important to develop and test landscape models in different biophysical settings. 相似文献
8.
There is an emerging recognition that natural lands and their conservation are important elements of a sustainable drinking
water infrastructure. We conducted a national, watershed-level environmental assessment of 5,265 drinking water watersheds
using data on land cover, hydrography and conservation status. Approximately 78% of the conterminous United States lies within
a drinking water watershed. The typical drinking water watershed had a high percentage of natural vegetation ([(x)\tilde] \tilde{x} = 77%) but a low percentage of it was set aside for conservation ([(x)\tilde] \tilde{x} = 3%). Median percentage values for urban and agriculture were 5 and 8%, respectively. Between ca. 1992 and ca. 2001, approximately
23% of the drinking water watersheds lost at least 1% of their natural vegetation, and approximately 9% of the watersheds
had at least a 1% increase in the amount of urban land. Loss of natural vegetation was common in nearly all areas of the country,
but also concentrated in the Ohio River and Southeast hydrologic regions. Urbanization was concentrated in the eastern United
States, primarily in the Mid-Atlantic and Southeast hydrologic regions. 相似文献
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10.
James D. Wickham Timothy G. Wade Kurt H. Riitters R.V. O'Neill Jonathan H. Smith Elizabeth R. Smith K.B. Jones A.C. Neale 《Landscape Ecology》2003,18(2):193-206
Nutrient export coefficients are estimates of the mass of nitrogen (N) or phosphorus (P) normalized by area and time (e.g.,
kg/ha/yr). They have been estimated most often for watersheds ranging in size from 102 to 104 hectares, and have been recommended as measurements to inform management decisions. At this scale, watersheds are often nested
upstream and downstream components of larger drainage basins, suggesting nutrient export coefficients will change from one
subwatershed to the next. Nutrient export can be modeled as risk where lack of monitoring data prevents empirical estimation.
We modeled N and P export risk for subwatersheds of larger drainage basins, and examined spatial changes in risk from upstream
to downstream watersheds. Spatial (subwatershed) changes in N and P risk were a function of in-stream decay, subwatershed
land-cover composition, and subwatershed streamlength. Risk tended to increase in a downstream direction under low rates of
in-stream decay, whereas high rates of in-stream decay often reduced risk to zero (0) toward downstream subwatersheds. On
average, increases in the modeled rate of in-stream decay reduced risk by 0.44 for N and 0.39 for P. Interactions between
in-stream decay, land-cover composition and streamlength produced dramatic changes in risk across subwatersheds in some cases.
Comparison of the null cases of no in-stream decay and homogeneously forested subwatersheds with extant conditions indicated
that complete forest cover produced greater reductions in nutrient export risk than a high in-stream decay rate, especially
for P. High rates of in-stream decay and complete forest cover produced approximately equivalent reductions in N export risk
for downstream subwatersheds.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献