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1.
Landscape influences on stream biotic integrity assessed at multiple spatial scales 总被引:31,自引:0,他引:31
The biological integrity of stream ecosystems depends critically on human activities that affect land use/cover along stream
margins and possibly throughout the catchment. We evaluated stream condition using an Index of Biotic Integrity (IBI) and
a habitat index (HI), and compared these measures to landscape and riparian conditions assessed at different spatial scales
in a largely agricultural Midwestern watershed. Our goal was to determine whether land use/cover was an effective predictor
of stream integrity, and if so, at what spatial scale. Twenty-three sites in first-through third-order headwater streams were
surveyed by electrofishing and site IBIs were calculated based on ten metrics of the fish collection. Habitat features were
characterized through field observation, and site HIs calculated from nine instream and bank metrics. Field surveys, aerial
photograph interpretation, and geographic information system (GIS) analyses provided assessments of forested land and other
vegetation covers at the local, reach, and regional (catchment) scales.
The range of conditions among the 23 sites varied from poor to very good based on IBI and HI scores, and habitat and fish
assemblage measures were highly correlated. Stream biotic integrity and habitat quality were negatively correlated with the
extent of agriculture and positively correlated with extent of wetlands and forest. Correlations were strongest at the catchment
scale (IBI with % area as agriculture, r2=0.50, HI with agriculture, r2=0.76), and tended to become weak and non-significant at local scales. Local riparian vegetation was a weak secondary predictor
of stream integrity. In this watershed, regional land use is the primary determinant of stream conditions, able to overwhelm
the ability of local site vegetation to support high-quality habitat and biotic communities. 相似文献
2.
Assessing the causes of stream impairments is challenging without a clear understanding of the spatiotemporal interactions among human infrastructure networks and hydrologic systems. Landscape change is often characterized using simplistic metrics that lump changes into generalized categories, such as impervious cover. We examined the evolution of human infrastructure in Panther Hollow, a small watershed in Pittsburgh, Pennsylvania to characterize the impacts of long-term (~100 years) landscape change on stream flow. Results show that impervious cover in the catchment grew from 3 % in 1900 to 27 % in 2010. Growth was non-linear, with 60 % of the development occurring between 1904 and 1930. We then compared two models that predict changes in annual water yield, one model based on watershed impervious cover and one based on human infrastructure arrangement. The model based solely on impervious cover predicts excessive amounts of surface runoff relative to the infrastructure model and monitored yield. This discrepancy occurs because the impervious model does not account for the diversion of 50 % of the watershed drainage through the combined sewer system to an adjacent basin. In the Panther Hollow watershed, hydrology is dominated by a reduction in water yield, contrasting typical hydrologic changes associated with urbanization. Our analysis reveals the value of quantifying additional landscape metrics, such as infrastructure pattern and connectivity, which provide a more complete understanding of how human development alters natural hydrology. 相似文献
3.
We assessed the influence of land cover at multiple spatial extents on fish assemblage integrity, and the degree to which
riparian forests can mitigate the negative effects of catchment urbanization on stream fish assemblages. Riparian cover (urban,
forest, and agriculture) was determined within 30 m buffers at longitudinal distances of 200 m, 1 km, and the entire network
upstream of 59 non-nested fish sampling locations. Catchment and riparian land cover within the upstream network were highly
correlated, so we were unable to distinguish between those variables. Most fish assemblage variables were related to % forest
and % urban land cover, with the strongest relations at the largest spatial extent of land cover (catchment), followed by
riparian land cover in the 1-km and 200-m reach, respectively. For fish variables related to urban land cover in the catchment,
we asked whether the influence of riparian land cover on fish assemblages was dependent on the amount of urban development
in the catchment. Several fish assemblage metrics (endemic richness, endemic:cosmopolitan abundance, insectivorous cyprinid
richness and abundance, and fluvial specialist richness) were all best predicted by single variable models with % urban land
cover. However, endemic:cosmopolitan richness, cosmopolitan abundance, and lentic tolerant abundance were related to % forest
cover in the 1-km stream reach, but only in streams that had <15% catchment urban land cover. In these cases, catchment urbanization
overwhelmed the potential mitigating effects of riparian forests on stream fishes. Together, these results suggest that catchment
land cover is an important driver of fish assemblages in urbanizing catchments, and riparian forests are important but not
sufficient for protecting stream ecosystems from the impacts of high levels of urbanization. 相似文献
4.
Paired aerial photographs were interpreted to assess recent changes in tree, impervious and other cover types in 20 U.S. cities as well as urban land within the conterminous United States. National results indicate that tree cover in urban areas of the United States is on the decline at a rate of about 7900 ha/yr or 4.0 million trees per year. Tree cover in 17 of the 20 analyzed cities had statistically significant declines in tree cover, while 16 cities had statistically significant increases in impervious cover. Only one city (Syracuse, NY) had a statistically significant increase in tree cover. City tree cover was reduced, on average, by about 0.27 percent/yr, while impervious surfaces increased at an average rate of about 0.31 percent/yr. As tree cover provides a simple means to assess the magnitude of the overall urban forest resource, monitoring of tree cover changes is important to understand how tree cover and various environmental benefits derived from the trees may be changing. Photo-interpretation of digital aerial images can provide a simple and timely means to assess urban tree cover change to help cities monitor progress in sustaining desired urban tree cover levels. 相似文献
5.
6.
Improved methods for quantifying potential nutrient interception by riparian buffers 总被引:1,自引:0,他引:1
Efforts to quantify the effects of riparian buffers on watershed nutrient discharges have been confounded by a commonly used analysis, which estimates buffer potential as the percentage of forest or wetland within a fixed distance of streams. Effective landscape metrics must instead be developed based on a clear conceptual model and quantified at the appropriate spatial scale. We develop new metrics for riparian buffers in two stages of increasing functional specificity to ask: (1) Which riparian metrics are more distinct from measures of whole watershed land cover? (2) Do functional riparian metrics provide different information than fixed-distance metrics? (3) How do these patterns vary within and among different physiographic settings? Using publicly available geographic data, we studied 503 watersheds in four different physiographic provinces of the Chesapeake Bay Drainage. In addition to traditional fixed-distance measures, we calculated mean buffer width, gap frequency, and measures of variation in buffer width using both “unconstrained” metrics and “flow-path” metrics constrained by surface topography. There were distinct patterns of relationship between watershed and near-stream land cover in each physiographic province and strong correlations with watershed land cover confounded fixed-distance metrics. Flow-path metrics were more independent of watershed land cover than either fixed-distance or unconstrained measures, but both functional metrics provided greater detail, interpretability, and flexibility than the fixed-distance approach. Potential applications of the new metrics include exploring the potential for land cover patterns to influence water quality, accounting for buffers in statistical nutrient models, quantifying spatial patterns for process-based modeling, and targeting management actions such as buffer restoration. 相似文献
7.
Riparian ecosystems are interfaces between aquatic and terrestrial environments recognized for their nutrient interception
potential in agricultural landscapes. Stream network maps from a broad range of map resolutions have been employed in watershed
studies of riparian areas. However, map resolution may affect important attributes of riparian buffers, such as the connectivity
between source lands and small stream channels missing in coarse resolution maps. We sought to understand the influence of
changing stream map resolution on measures of the river network, near-stream land cover, and riparian metrics. Our objectives
were: (1) to evaluate the influence of stream map resolution on measures of the stream network, the character and extent of
near-stream zones, and riparian metrics; (2) to compare patterns of variation among different physiographic provinces; and
(3) to explore how predictions of nutrient retention potential might be affected by the resolution of a stream map. We found
that using fine resolution stream maps significantly increased our estimates of stream order, drainage density, and the proportion
of watershed area occurring near a stream. Increasing stream map resolution reduced the mean distance to source areas as well
as mean buffer width and increased the frequency of buffer gaps. Measures of percent land cover within 100 m of streams were
less sensitive to stream map resolution. Overall, increasing stream map resolution led to reduced estimates of nutrient retention
potential in riparian buffers. In some watersheds, switching from a coarse resolution to a fine resolution stream map completely
changed our perception of a stream network from well buffered to largely unbuffered. Because previous, broad-scale analyses
of riparian buffers used coarse-resolution stream maps, those studies may have overestimated landscape-level buffer prevalence
and effectiveness. We present a case study of three watersheds to demonstrate that interactions among stream map resolution
and land cover patterns make a dramatic difference in the perceived ability of riparian buffers to ameliorate effects of agricultural
activities across whole watersheds. Moreover, stream map resolution affects inferences about whether retention occurs in streams
or riparian zones. 相似文献
8.
We present a parametric model for estimating the areas within watersheds whose land use best predicts indicators of stream
ecological condition. We regress a stream response variable on the distance-weighted proportion of watershed area that has
a specific land use, such as agriculture. Distance weighting functions model the declining influence of landscape elements
as a function of their flowpath distances, first to the stream channel (to-stream distance), and then down the channel to
the location at which stream condition was sampled (in-stream distance). Model parameters specify different distance scales
over which to-stream and in-stream influences decline. As an example, we predict an index of biotic integrity (IBI) for the
fish communities in 50 small streams of the Willamette Basin of Oregon, USA, from distance-weighted proportions of agricultural
or urban land use in their watersheds. The weighting functions of best-fitting models (R
2 = 0.57) represent landscape influence on IBI as extending upstream tens of kilometers along the stream channel network, while
declining nearly to zero beyond a distance of 30 m from the channel. Our example shows how parametric distance weighting can
identify the distance scales, and hence the approximate areas within watersheds, for which land use is most strongly associated
with a stream response variable. In addition, distance-weighting parameters offer a simple and direct language for comparing
the scales of landscape influence on streams across different land uses and stream ecosystem components. 相似文献
9.
Landscape change is an ongoing process for even the most established landscapes, especially in context to urban intensification and growth. As urbanization increases over the next century, supporting bird species’ populations within urbanizing areas remains an important conservation challenge. Fundamental elements of the biophysical structure of urban environments in which bird species likely respond include tree cover and human infrastructure. We broadly examine how tree cover and urban development structure bird species distributions along the urban-rural gradient across multiple spatial scales. We established a regional sampling design within the Oak Openings Region of northwestern, Ohio, USA, to survey bird species distributions across an extensive urbanization gradient. Through occupancy modeling, we obtained standardized effects of bird species response to local and landscape-scale predictors and found that landscape tree cover influenced the most species, followed by landscape impervious surface, local building density, and local tree cover. We found that responses varied according to habitat affiliation and migratory distance of individual bird species. Distributions of short-distance, edge habitat species located towards the rural end of the gradient were explained primarily by low levels of urbanization and potential vegetative and supplemental resources associated with these areas, while forest species distributions were primarily related to increasing landscape tree cover. Our findings accentuate the importance of scale relative to urbanization and help target where potential actions may arise to benefit bird diversity. Management will likely need to be implemented by municipal governments and agencies to promote tree cover at landscape scale, followed by residential land management education for private landowners. These approaches will be vital in sustaining biodiversity in urbanizing landscapes as urban growth expands over the next century. 相似文献
10.
We explored land use, fish assemblage structure, and stream habitat associations in 20 catchments in Opequon Creek watershed, West Virginia. The purpose was to determine the relative importance of urban and agriculture land use on stream biotic integrity, and to evaluate the spatial scale (i.e., whole-catchment vs riparian buffer) at which land use effects were most pronounced. We found that index of biological integrity (IBI) scores were strongly associated with extent of urban land use in individual catchments. Sites that received ratings of poor or very poor based on IBI scores had > 7% of urban land use in their respective catchments. Habitat correlations suggested that urban land use disrupted flow regime, reduced water quality, and altered stream channels. In contrast, we found no meaningful relationship between agricultural land use and IBI at either whole-catchment or riparian scales despite strong correlations between percent agriculture and several important stream habitat measures, including nitrate concentrations, proportion of fine sediments in riffles, and the abundance of fish cover. We also found that variation in gradient (channel slope) influenced responses of fish assemblages to land use. Urban land use was more disruptive to biological integrity in catchments with steeper channel slopes. Based on comparisons of our results in the topographically diverse Opequon Creek watershed with results from watersheds in flatter terrains, we hypothesize that the potential for riparian forests to mitigate effects of deleterious land uses in upland portions of the watershed is inversely related to gradient.This revised version was published online in May 2005 with corrections to the Cover Date. 相似文献
11.
Impervious surfaces are a ubiquitous urban feature that increase temperature and tree drought stress and are a demonstrated indicator of Acer rubrum L. tree condition and insect pest abundance. We examined the relationship between A. rubrum condition, impervious surface cover, and Melanaspis tenebricosa (Comstock) abundance, a primary herbivore of urban A. rubrum, in eight cities across the southern distribution of A. rubrum. We predicted that the effects of warming, due to impervious surface, would be greater in warmer southern cities than in cooler northern cities. We found that impervious surface was a robust predictor of tree condition, but this effect was not significantly affected by background temperature. Melanaspis tenebricosa abundance was a function of impervious surface and background temperature, with greatest abundances occurring at mid latitudes. Based on these relationships, we developed impervious surface thresholds to inform site selection for A. rubrum throughout the southeastern USA. Planting criteria based on habitat characteristics should maximize urban tree longevity and services provided. 相似文献
12.
Impacts of road corridors on urban landscape pattern: a gradient analysis with changing grain size in Shanghai, China 总被引:4,自引:0,他引:4
Urbanization is one of the most important driving forces for land use and land cover change. Quantifying urban landscape pattern
and its change is fundamental for monitoring and assessing ecological and socioeconomic consequences of urbanization. As the
largest city in the country, Shanghai is now the fastest growing city in China. Using land use data set of 2002 and combining
gradient analysis with landscape metrics, we analyzed landscape pattern of Shanghai with increasing grain size to study the
impacts of road corridors on urban landscape pattern. Landscape metrics were computed along a 51×9 km2 transect cutting across Shanghai with a moving window. The results showed that the urban landscape pattern of Shanghai was
greatly changed when road corridors were merged with urban patches and the variation of patch density would alter when grain
size changed. As a linear land use type, road corridors exhibited a different spatial signature comparing with other land
use types and distinctive behavior with increasing grain size. Merging road and urban patches resulted in a sharp reduction
in patch density, mainly caused by segmentation of roads corridors. The results suggested that grain size around 7.5 m might
be optimal for urban landscape analysis. Landscape patch density is significantly correlated with road percent coverage and
the most important effect of road corridors in urban landscape is increased habitat fragmentation. 相似文献
13.
Urban trees store and sequester large amounts of carbon and are a vital component of natural climate solutions. Despite the well-recognized carbon benefits of urban trees, there is limited effort to examine how spatial distribution of carbon density varies across distinctive social, demographic, and built dimensions of urban landscapes. Moreover, it is unclear whether specific aspects of landscape structure and design could help increase carbon densities in urban trees. Here, we produced a fine-resolution carbon density map of urban trees in New York City (NYC) by integrating high-resolution land cover map, LiDAR-derived tree metrics, i-Tree Eco, and field survey data. We then explored spatial variations of carbon density across the gradients of urban development intensity, social deprivation index, and neighborhood age, and we examined the relationships between carbon density, and fragmentation, aggregation, size, and shape of tree canopy cover. We find that carbon stored in urban trees in NYC is estimated as 1078 Gg, with an average density of 13.8 Mg/ha. This large amount of carbon is unevenly distributed, with carbon densities being highest in Bronx and in open parks and street trees. Furthermore, carbon densities are negatively associated with urban development intensity and the social gradient of deprivation. Regarding the impacts of tree morphology on carbon density, our results show that while the amount of tree cover is the most influential factor in determining carbon density, small-sized forest patches and moderate levels of forest edges are also conductive to increasing carbon densities of urban trees. To incorporate urban forestry into developing innovative, effective, and equitable climate mitigation strategies, planners and decision makers need to identify the optimal spatial configuration of urban forests and invest in tree planting programs in marginalized communities. 相似文献
14.
Robert L. HopkinsII 《Landscape Ecology》2009,24(7):943-955
The distributions of freshwater mussels are controlled by landscape factors operating at multiple spatial scales. Changes
in land use/land cover (LULC) have been implicated in severe population declines and range contractions of freshwater mussels
across North America. Despite widespread recognition of multiscale influences few studies have addressed these issues when
developing distribution models. Furthermore, most studies have disregarded the role of landscape pattern in regulating aquatic
species distributions, focusing only on landscape composition. In this study, the distribution of Rabbitsfoot (Quadrula cylindrica) in the upper Green River system (Ohio River drainage) is modeled with environmental variables from multiple scales: subcatchment,
riparian buffer, and reach buffer. Four types of landscape environment metrics are used, including: LULC pattern, LULC composition,
soil composition, and geology composition. The study shows that LULC pattern metrics are very useful in modeling the distribution
of Rabbitsfoot. Together with LULC compositional metrics, pattern metrics permit a more detailed analysis of functional linkages
between aquatic species distributions and landscape structure. Moreover, the inclusion of multiple spatial scales is necessary
to accurately model the hierarchical processes in stream systems. Geomorphic features play important roles in regulating species
distributions at intermediate and large scales while LULC variables appear more influential at proximal scales. 相似文献
15.
Landscape,community, countryside: linking biophysical and social scales in US Corn Belt agricultural landscapes 总被引:1,自引:1,他引:0
Understanding the interplay between ecological and social factors across multiple scales is integral to landscape change initiatives
in productive agricultural regions such as the rural US Corn Belt. We investigated the cultural context surrounding the use
of perennial cover types—such as stream buffers, wetlands, cellulosic bioenergy stocks, and diverse cropping rotations—to
restore water quality, biodiversity, and ecosystem function within a Corn Belt agricultural mosaic in Iowa, USA. Through ethnographic
techniques and 33 in-depth interviews, we examined what was most important to rural stakeholders about their countryside.
We then used photo elicitation to probe how interviewees’ assessments of farm practices involving perennial cover types were
related to their sense of place. Our interviewees perceived their rural “countryside” as a linked social and biophysical entity,
identifying strongly with the farming lifestyle and with networks of people across the landscape. While most interviewees
approved of perennial farm practices on marginal agricultural land, implementation of these practices was neither a priority
nor strongly assimilated into rural experience and ethics. We identified three scale boundaries in our interviewees’ perception
of place which present key challenges and opportunities for landscape change: landscape-community, individual-community, and
community-institution. In all cases, community social norms and networks—exhibited at landscape spatial scales—may be instrumental
in bridging these boundaries and enabling networks of perennial cover types that span privately owned and operated farms.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
16.
Paired aerial photographs were interpreted to assess recent changes (c. 2009–2014) in tree, impervious and other cover types within urban/community and urban land in all 50 United States and the District of Columbia. National results indicate that tree cover in urban/community areas of the United States is on the decline at a rate of about 175,000 acres per year, which corresponds to approximately 36 million trees per year. Estimated loss of benefits from trees in urban areas is conservatively valued at $96 million per year. Overall, for both urban and the broader urban/community areas, 23 states/districts had statistically significant declines in tree cover, 25 states had non-significant decreases or no change in tree cover, and three states showed a non-significant increase in tree cover. The most intensive change occurred within urban areas, with tree cover in these areas dropping one percent over the 5-year period, compared to a 0.7 percent drop in urban/community areas. States/districts with the greatest statistically significant annual decline in percent urban tree cover were: Oklahoma (−0.92%/yr), District of Columbia (−0.44%/yr), Rhode Island (−0.40%/yr), Oregon (−0.38%/yr) and Georgia (−0.37%/yr). Coinciding with the loss of tree cover was a gain in impervious cover, with impervious cover increasing 0.6 percent in urban/community areas and 1.0 percent in urban areas over the 5-year period. Such changes in cover types affect the benefits derived from urban forests and consequently the health and well-being of urban residents. 相似文献
17.
Freshwater research and management efforts could be greatly enhanced by a better understanding of the relationship between landscape-scale factors and water quality indicators. This is particularly true in urban areas, where land transformation impacts stream systems at a variety of scales. Despite advances in landscape quantification methods, several studies attempting to elucidate the relationship between land use/land cover (LULC) and water quality have resulted in mixed conclusions. However, these studies have largely relied on compositional landscape metrics. For urban and urbanizing watersheds in particular, the use of metrics that capture spatial pattern may further aid in distinguishing the effects of various urban growth patterns, as well as exploring the interplay between environmental and socioeconomic variables. However, to be truly useful for freshwater applications, pattern metrics must be optimized based on characteristic watershed properties and common water quality point sampling methods. Using a freely available LULC data set for the Santa Clara Basin, California, USA, we quantified landscape composition and configuration for subwatershed areas upstream of individual sampling sites, reducing the number of metrics based on: (1) sensitivity to changes in extent and (2) redundancy, as determined by a multivariate factor analysis. The first two factors, interpreted as (1) patch density and distribution and (2) patch shape and landscape subdivision, explained approximately 85% of the variation in the data set, and are highly reflective of the heterogeneous urban development pattern found in the study area. Although offering slightly less explanatory power, compositional metrics can provide important contextual information. 相似文献
18.
Associations between soil carbon and ecological landscape variables at escalating spatial scales in Florida,USA 总被引:1,自引:1,他引:0
The spatial distribution of soil carbon (C) is controlled by ecological processes that evolve and interact over a range of
spatial scales across the landscape. The relationships between hydrologic and biotic processes and soil C patterns and spatial
behavior are still poorly understood. Our objectives were to (i) identify the appropriate spatial scale to observe soil total
C (TC) in a subtropical landscape with pronounced hydrologic and biotic variation, and (ii) investigate the spatial behavior
and relationships between TC and ecological landscape variables which aggregate various hydrologic and biotic processes. The
study was conducted in Florida, USA, characterized by extreme hydrologic (poorly to excessively drained soils), and vegetation/land
use gradients ranging from natural uplands and wetlands to intensively managed forest, agricultural, and urban systems. We
used semivariogram and landscape indices to compare the spatial dependence structures of TC and 19 ecological landscape variables,
identifying similarities and establishing pattern–process relationships. Soil, hydrologic, and biotic ecological variables
mirrored the spatial behavior of TC at fine (few kilometers), and coarse (hundreds of kilometers) spatial scales. Specifically,
soil available water capacity resembled the spatial dependence structure of TC at escalating scales, supporting a multi-scale
soil hydrology-soil C process–pattern relationship in Florida. Our findings suggest two appropriate scales to observe TC,
one at a short range (autocorrelation range of 5.6 km), representing local soil-landscape variation, and another at a longer
range (119 km), accounting for regional variation. Moreover, our results provide further guidance to measure ecological variables
influencing C dynamics. 相似文献
19.
20.
The transformation of natural landscapes into impervious built-up surfaces through urbanization is known to significantly interfere with the ecological integrity of urban landscapes and accelerate climate change and associated impacts. Although urban reforestation is widely recognised as an ideal mitigation practice against these impacts, it often has to compete with other lucrative land uses within an urban area. The often limited urban space provided for reforestation therefore necessitates the optimization of the ecological benefits, which demands spatially explicit information. The recent proliferation of tree stands structural complexity (SSC) and topographic data offer great potential for determining the ecological performance of reforested areas across an urban landscape. This study explores the potential of using topographic datasets to predict SSC in a reforested urban landscape and ranks the value of these topographic variables in determining SSC. Tree structural data from a reforested urban area was collected and fed into a tree stand structural complexity index, which was used to indicate ecological performance. Topographic variables (Topographic Wetness Index, slope, Area Solar Radiation and elevation)- were derived from a Digital Elevation Model (DEM) and used to predict SSC using the Partial Least Squares (PLS) regression technique. Results show that SSC varied significantly between the topographic variables. Results also show that the topographic variables could be used to reliably predict SSC. As expected, the Topographic Wetness Index and slope were the most important topographic determinants of SSC while elevation was the least valuable. These results provide valuable spatially explicit information about the ecological performance of the reforested areas within an urban landscape. Specifically, the study demonstrates the value of topographic data as aids to urban reforestation planning. 相似文献