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1.
Guangzhou city in South China has experienced an accelerated urban development since the 1980s. This paper examines the impact of the urban development on urban heat islands through a historical analysis of urban-rural air temperature differences. Remote sensing techniques were applied to derive information on land use/cover and land surface temperatures and to assess the thermal response patterns of land cover types. The results revealed an overriding importance of urban land cover expansion in the changes in heat island intensity and surface temperature patterns. Urban development was also related to a continual air temperature increase in the 1980s and 1990s. The combined use of satellite-derived vegetation and land cover distributions with land surface temperature maps provides a potential useful tool for many planning applications. The city's greening campaigns and landscaping designs should consider the different cooling effects of forest, shrubs and grassy lawns for temperature control and should plant more tall trees.  相似文献   

2.
The floodplain of the river Strymon at Kerkini (northern Greece) was transformed into an irrigation reservoir by the construction of a dam in 1932 and subsequently enlarged in 1982. The aims of this study were to quantify the changes occurring in the various habitat types following raising of the waterlevel and to assess the stability of the plant communities present at this Ramsar site. The current hydrological regime, which has been stable since 1986, is typified by an increase in mean annual reservoir level of 2.2 m and by an increase in the annual range in level of 1.3 m. Landsat (1980, 1981, 1984, 1986, and 1988) and SPOT (1990) satellite images show a decrease in the area of grassland and shallow water areas, the very rapid disappearance of reedbeds, the appearance of beds ofNymphaea and the disappearance of half the forest area. The flooded forest, dominated bySalix alba, is a key habitat contributing to the biological richness of this wetland of international importance. The decrease in the forested area will continue because of the death of standing trees, the absence of regeneration under the new regime, the felling of trees and grazing. Management could be undertaken to ensure the survival of forested habitat and reedbeds at Kerkini, but this would require that the authorities take into account nature conservation and the protected status of the site and not raise the water level again.  相似文献   

3.
Representative Landscapes in the Forested Area of Canada   总被引:1,自引:0,他引:1  
Canada is a large nation with forested ecosystems that occupy over 60% of the national land base, and knowledge of the patterns of Canada’s land cover is important to proper environmental management of this vast resource. To this end, a circa 2000 Landsat-derived land cover map of the forested ecosystems of Canada has created a new window into understanding the composition and configuration of land cover patterns in forested Canada. Strategies for summarizing such large expanses of land cover are increasingly important, as land managers work to study and preserve distinctive areas, as well as to identify representative examples of current land-cover and land-use assemblages. Meanwhile, the development of extremely efficient clustering algorithms has become increasingly important in the world of computer science, in which billions of pieces of information on the internet are continually sifted for meaning for a vast variety of applications. One recently developed clustering algorithm quickly groups large numbers of items of any type in a given data set while simultaneously selecting a representative—or “exemplar”—from each cluster. In this context, the availability of both advanced data processing methods and a nationally available set of landscape metrics presents an opportunity to identify sets of representative landscapes to better understand landscape pattern, variation, and distribution across the forested area of Canada. In this research, we first identify and provide context for a small, interpretable set of exemplar landscapes that objectively represent land cover in each of Canada’s ten forested ecozones. Then, we demonstrate how this approach can be used to identify flagship and satellite long-term study areas inside and outside protected areas in the province of Ontario. These applications aid our understanding of Canada’s forest while augmenting its management toolbox, and may signal a broad range of applications for this versatile approach.  相似文献   

4.
This study focuses on the relationships of watershed runoff with historical land use/land cover (LULC) and climate trends. Over the 20th Century, LULC in the Southeast United States, particularly the North Carolina Piedmont, has evolved from an agriculture dominated to an extensively forested landscape with more recent localized urbanization. The regrowth of forest has an important influence on the hydrology of the region as it enhances ecosystem interaction with recent climate change. During 1920‐2009, the amount of precipitation in some parts of the North Carolina Piedmont forest regrowth area showed increasing trends without corresponding increments in runoff. We employed the Soil and Water Assessment Tool (SWAT) to backcast long‐term hydrologic behavior of watersheds in North Carolina with different LULC conditions: (1) LULC conversion from agricultural to forested area and (2) long‐term stable forested area. Comparing U.S. Geological Survey‐measured stream discharge with SWAT‐simulated stream discharge under the assumption of constant 2006 LULC, we found significant stream discharge underprediction by SWAT in two LULC conversion watersheds during the early simulation period (1920s) with differences gradually decreasing by the mid‐1970s. This model bias suggests that forest regrowth on abandoned agricultural land was a key factor contributing to mitigate the impact of increased precipitation on runoff due to increasing water consumption driven by changes in vegetation.  相似文献   

5.
ABSTRACT: About 50 to 80 percent of precipitation in the southeastern United States returns to the atmosphere by evapotranspiration. As evapotranspiration is a major component in the forest water balances, accurately quantifying it is critical to predicting the effects of forest management and global change on water, sediment, and nutrient yield from forested watersheds. However, direct measurement of forest evapotranspiration on a large basin or a regional scale is not possible. The objectives of this study were to develop an empirical model to estimate long‐term annual actual evapotranspiration (ART) for forested watersheds and to quantify spatial AET patterns across the southeast. A geographic information system (GIS) database including land cover, daily streamflow, and climate was developed using long term experimental and monitoring data from 39 forested watersheds across the region. Using the stepwise selection method implemented in a statistical modeling package, a long term annual AET model was constructed. The final multivariate linear model includes four independent variables—annual precipitation, watershed latitude, watershed elevation, and percentage of forest coverage. The model has an adjusted R2 of 0.794 and is sufficient to predict long term annual ART for forested watersheds across the southeastern United States. The model developed by this study may be used to examine the spatial variability of water availability, estimate annual water loss from mesoscale watersheds, and project potential water yield change due to forest cover change.  相似文献   

6.
ABSTRACT

The number of households migrating to agricultural villages has sharply increased in the Republic of Korea (South Korea) since the late 1990s when the Asian economic crisis developed. This study investigates the environmental behaviour and the socio-economic characteristics of urban-rural migrant farming households and provides insights into their significance for rural sustainability in South Korea. The study is based on survey data collected in 2016 from a sample of 166 migrant farming households and 46 native farming households from the Namwon region in South Korea. The migrant farming households are divided into 29 return and 137 non-return farming households. It was found that most non-return migrants are organic farmers, and can be characterised as anti-urban, amenity-pursuing, green, and lifestyle migrants. It is no wonder that they have a strong intent to make their new home an environmentally, socially and economically sustainable place for their children. Thus, appropriate policy measures need to be designed in such a way to facilitate the synergy between the repopulation of rural areas by farming migrants, their uptake of organic farming, their active engagement in community rebuilding, and regional economic development.  相似文献   

7.
Urbanization and the Loss of Resource Lands in the Chesapeake Bay Watershed   总被引:3,自引:0,他引:3  
We made use of land cover maps, and land use change associated with urbanization, to provide estimates of the loss of natural resource lands (forest, agriculture, and wetland areas) across the 168,000 km2 Chesapeake Bay watershed. We conducted extensive accuracy assessments of the satellite-derived maps, most of which were produced by us using widely available multitemporal Landsat imagery. The change in urbanization was derived from impervious surface area maps (the built environment) for 1990 and 2000, from which we estimated the loss of resource lands that occurred during this decade. Within the watershed, we observed a 61% increase in developed land (from 5,177 to 8,363 km2). Most of this new development (64%) occurred on agricultural and grasslands, whereas 33% occurred on forested land. Some smaller municipalities lost as much as 17% of their forest lands and 36% of their agricultural lands to development, although in the outlying counties losses ranged from 0% to 1.4% for forests and 0% to 2.6% for agriculture. Fast-growing urban areas surrounded by forested land experienced the most loss of forest to impervious surfaces. These estimates could be used for the monitoring of the impacts of development across the Chesapeake Bay watershed, and the approach has utility for other regions nationwide. In turn, the results and the approach can help jurisdictions set goals for resource land protection and acquisition that are consistent with regional restoration goals.  相似文献   

8.
It is usually inappropriate to define rectangular land areas or administrative units as the extent for quantifying landscapes that possess hierarchical structure. As a functional unit established by geophysical relationships, the watershed is one of many natural scales in the hierarchical landscape. We examined the dynamics of the Yashiro watershed of Japan at the landscape level using pattern metrics based on Landsat thematic mapper (TM) imagery from 1985 to 1998. This watershed provides important habitats for the hooded crane (Grus monachus), a vulnerable species. While its world population has remained stable, the number wintering at Yashiro has declined in recent years. Changes in landscape metrics reveal that the spatial pattern within the watershed underwent homogenization due to depopulation of local people and shifts in local energy requirements and forest management policy at Yashiro. Specific changes include: a decrease in bare land area from 6.2% to 1.0% of the landscape, increased forest cover from 69.2% to 76.1%, reduction in patch number from 1194 to 616 and enlarged mean patch size, and a decrease in total edge from 223,740 m to 158,040 m. The rate of change in landscape metrics indicates a rapid change towards homogeneity in the landscape since 1990. The temporal changes in hooded crane populations corresponded to the changes in landscape. An alternative explanation has been proposed that decline of the species is influenced by landscape dynamics affecting both habitat selection and food resources. Conservation at the watershed scale is suggested to be complementary to the current conservation measures of the species.  相似文献   

9.
/ European settlement began in the Lower Fraser Basin (LFB) inwestern British Columbia in 1827 and has impacted the basin ecosystem in anumber of ways, especially affecting the vegetation. Using previouslypublished data, air photos, and other historical material for the area,estimates of land cover were made for the years prior to 1827 and for 1930and 1990. The area of coniferous forest changed from 71% prior to 1827to 50% in 1930 to 54% in 1990. However, prior to 1827, only27% of the forest would have been immature (<120 years old), while40% would have been immature in 1930 and 73% of the forest wasimmature in 1990. The amount of wetland area decreased from 10% to1% of the study area while urban and agricultural area increased to26% of the study area by 1990. The changes in land cover have hadadverse effects on soil, water, and air quality; aquatic life; and plant andanimal populations. Estimates of changes in net primary production andorganic soil carbon suggest a decline over the past 170 years, although thelatter rate of decrease has slowed since 1930. As human populations in theLower Fraser Basin continue to increase, the quality of air, water, and soilwill continue to decline unless measures are taken.KEY WORDS: Human impact; Land cover; Net primary productivity; Organiccarbon in soil  相似文献   

10.
The solution chemistry of forested streams primarily in western North America is explained by considering the major factors that influence this chemistry — geological weathering; atmospheric precipitation and climate; precipitation acidity; terrestrial biological processes; physical/chemical reactions in the soil; and physical, chemical, and biological processes within streams. Due to the complexity of all these processes and their varying importance for different chemicals, stream water chemistry has exhibited considerable geographic and temporal variation and is difficult to model accurately. The impacts of forest harvesting on stream water chemistry were reviewed by considering the effects of harvesting on each of the important factors controlling this chemistry, as well as other factors influencing these impacts ‐ extent of the watershed harvested, presence of buffer strips between streams and harvested areas, nature of post‐harvesting site preparation, revegetation rate following harvesting, pre‐harvesting soil fertility, and soil buffering capacity. These effects have sometimes reinforced one another but have sometimes been counterbalancing or slight so that harvesting impacts on stream water chemistry have been highly variable. Eight major knowledge gaps were identified, two of which — a scarcity of detailed stream chemical budgets and knowledge of longitudinal variation in stream chemistry — relate to undisturbed streams, while the remainder relate to forest harvesting effects.  相似文献   

11.
We developed logistic regression models from data on biotic and abiotic variables for 172 sites on Banks Peninsula, New Zealand, to predict the probability of occurrence of two diadromous fish, banded kokopu (Galaxias fasciatus) and koaro (G. brevipinnis). Banded kokopu occurrence was positively associated with small streams and low-intensity land uses (e.g., sheep grazing or forested), whereas intensive land uses (e.g., mixed sheep and cattle farming) and lack of riparian forest cover impacted negatively on occurrence at sampled sites. Also, if forests were positioned predominantly in lowland areas, banded kokopu occurrence declined with increasing distance to stream mouth. Koaro occurrence was positively influenced by catchment forest cover, high stream altitudes, and areas of no farming activity or mixed land uses. Intensive land uses, distance to stream mouth, and presence of banded kokopu negatively influenced koaro occupancy of stream reaches. Banded kokopu and koaro presence was predicted in 86.0% and 83.7% agreement, respectively, with field observations. We used the models to quantify the amount of stream reaches that would be of good, moderate, and poor quality, based on the probability of occurrences of the fish being greater than 0.75, between 0.75 and 0.5, or less than 0.5, respectively. Hindcasting using historical data on vegetation cover undertaken for one catchment, Pigeon Bay, showed they would have occupied most of the waterway before anthropogenic modification. We also modeled potential future scenarios to project potential fish distribution.  相似文献   

12.
This study assessed changes in forest cover in a mountain watershed in central Nepal between 1976 and 2000 by comparing classified satellite images coupled by GIS analyses, and examined the association of forest change with major physiographic, economic, and local forest governance parameters. The results showed an increase in forested area (forest plus shrublands) by 7.6% during 1976–2000. Forest dynamism (changes including improvement, deterioration, gain, and loss) was highest in low-elevation, south-facing and less-steep slopes that were closer to roads. Proportionately the highest net improvement and gain to forested area also took place in those locations. Forest degradation occurred at twice the rate of improvement in high elevation areas (> 2300 m). Forests located in urban and semiurban areas (i.e., a market-oriented economy) experienced a proportionately higher amount of net improvement and gain than forests in rural areas (i.e., a subsistence economy). Among the three governance arrangements, proportionately the highest net improvement and gain took place in semigovernment forests (forested area legally under the forest department but with de facto control and claim of ownership by local communities and/or municipality) followed by formalized community forests (including leasehold). Government forests, which were mostly found in the southern high mountains and had virtually open access, remained relatively stable during the study period. Over 50% of the watershed forests have not come under community-based management despite favorable policy and more than two decades of government intervention with continuous donor support. The findings indicate that the present one size fits all approach of community forest handover policy in Nepal needs rethinking to accommodate biophysical and socioeconomic variations across the country.  相似文献   

13.
ABSTRACT: Coastal watersheds in the southeastern United States are rapidly changing due to population growth and attendant increases in residential development, industry, and tourism related commerce. This research examined spatial and temporal patterns of nutrient concentrations in streams from 10 small watersheds (< 4 km2) that drain into Murrells Inlet (impacted) and North Inlet (pristine), two high salinity estuaries along the South Carolina coast. Monthly grab samples were collected during baseflow during 1999 and analyzed for total and dissolved inorganic and organic forms of nitrogen and phosphorus. Data were grouped into forested wetland creeks (representing predevelopment reference sites), urban creeks, and urban ponds. DON and NH4 concentrations were greater in forested streams than in urban streams. NO3 and TP concentrations were greatest in urban streams. Seasonally, concentrations were highest during summer for TN, NH4, DON, and TP, while NO3 concentrations were greatest during winter. Nutrient ratios clearly highlighted the reduction in organic nitrogen due to coastal development. Multiple regression models to predict instream nutrient concentrations from land use in Murrells Inlet suggest that effects are not significant (small r2). The findings indicate that broad land use/land cover classes cannot be used to predict nutrient concentrations in streams in the very small watersheds in our study areas.  相似文献   

14.
Acid rain in Asia   总被引:3,自引:0,他引:3  
Acid rain has been an issue of great concern in North America and Europe during the past several decades. However, due to the passage of a number of recent regulations, most notably the Clean Air Act in the United States in 1990, there is an emerging perception that the problem in these Western nations is nearing solution. The situation in the developing world, particularly in Asia, is much bleaker. Given the policies of many Asian nations to achieve levels of development comparable with the industrialized world—which necessitate a significant expansion of energy consumption (most derived from indigenous coal reserves)—the potential for the formation of, and damage from, acid deposition in these developing countries is very high. This article delineates and assesses the emissions patterns, meteorology, physical geology, and biological and cultural resources present in various Asian nations. Based on this analysis and the risk factors to acidification, it is concluded that a number of areas in Asia are currently vulnerable to acid rain. These regions include Japan, North and South Korea, southern China, and the mountainous portions of Southeast Asia and southwestern India. Furthermore, with accelerated development (and its attendant increase in energy use and production of emissions of acid deposition precursors) in many nations of Asia, it is likely that other regions will also be affected by acidification in the near future. Based on the results of this overview, it is clear that acid deposition has significant potential to impact the Asian region. However, empirical evidence is urgently needed to confirm this and to provide early warning of increases in the magnitude and spread of acid deposition and its effects throughout this part of the world.  相似文献   

15.
ABSTRACT: Significant land cover changes have occurred in the watersheds that contribute runoff to the upper San Pedro River in Sonora, Mexico, and southeast Arizona. These changes, observed using a series of remotely sensed images taken in the 1970s, 1980s, and 1990s, have been implicated in the alteration of the basin hydrologic response. The Cannonsville subwatershed, located in the Catskill/Delaware watershed complex that delivers water to New York City, provides a contrast in land cover change. In this region, the Cannonsville watershed condition has improved over a comparable time period. A landscape assessment tool using a geographic information system (GIS) has been developed that automates the parameterization of the Soil and Water Assessment Tool (SWAT) and KINEmatic Runoff and EROSion (KINEROS) hydrologic models. The Automated Geospatial Watershed Assessment (AGWA) tool was used to prepare parameter input files for the Upper San Pedro Basin, a subwatershed within the San Pedro undergoing significant changes, and the Cannonsville watershed using historical land cover data. Runoff and sediment yield were simulated using these models. In the Cannonsville watershed, land cover change had a beneficial impact on modeled watershed response due to the transition from agriculture to forest land cover. Simulation results for the San Pedro indicate that increasing urban and agricultural areas and the simultaneous invasion of woody plants and decline of grasslands resulted in increased annual and event runoff volumes, flashier flood response, and decreased water quality due to sediment loading. These results demonstrate the usefulness of integrating remote sensing and distributed hydrologic models through the use of GIS for assessing watershed condition and the relative impacts of land cover transitions on hydrologic response.  相似文献   

16.
Timber was harvested on South Fork of Thomas Creek, White Mountains of Arizona, USA, for the first time in 1978–1979. This caused significant increases in annual flow volumes and annual instantaneous peak flows. North Fork remained untouched, but both streams were in disequilibrium before harvest time. Due to wetter years during the postharvest period, North Fork also experienced some flow increases, but the difference was not significant. Flow increases cause increased erosion in disequilibrium channels. While in South Fork channel cross sections enlarged by 10% since preharvest time, those in North Fork enlarged by only 2.5%. The number of knickpoints tripled in South Fork, which was about double that in North Fork. Knickpoint development resulted in destruction of the natural control structures (log steps and transverse gravel bars) in South Fork (47%), while in North Fork they increased by 23%. Knickpoints are scarps on the channel bed that have the appearance of gully headcuts. The tripling of the number of knickpoints signifies that adjustment processes of the bed profile are intensified drastically in South Fork. The geomorphic changes signify that due to increases in discharge, the extent of disequilibrium is exacerbated in South Fork. Yet, volumes of erosion are relatively small, as will be sediment volumes leaving the watershed at a given time, because of the stepwise sediment transport occurring in this ephemeral stream.  相似文献   

17.
The fisher (Martes pennanti) has recently recovered from historic extirpations across much of its geographic range. There are at least five explanations for the recovery of the fisher, including changes in the amount of habitat, the suitability of habitat, trapping pressure, societal attitudes toward predators, and climate. We evaluated a recovering fisher population in Ontario to test two conditions we viewed as necessary to support the hypothesis that fisher populations have increased due to an increase in the amount of forested land. First, we tested whether the amount of forested land has increased. Second, we tested whether contemporary fisher abundance (and therefore habitat quality) was related to the amount of forest. Topographic maps showed that the proportion of forested land in the study area had increased by 1.9% per decade since 1934 and 3.3% per decade since 1959, likely as a result of land conversion from agricultural uses. Overall the proportion of the study area that was forested increased from 29% to 40% during 1934 to 1995. Census data from the region indicated that there had been a decline in the amount of land area being farmed during the last 50 years. Recent livetrapping data showed that fisher abundance was positively related to the proportion of landscapes that were forested. Based on our results, we could not reject the hypothesis that an increase in the amount of forested land has contributed to the recovery of fisher populations.  相似文献   

18.
One of the largest changes in US forest type areas over the last half-century has involved pine types in the South. The area of planted pine has increased more than 10-fold since 1950, mostly on private lands. Private landowners have responded to market incentives and government programs, including subsidized afforestation on marginal agricultural land. Timber harvest is a crucial disturbance affecting planted pine area, as other forest types are converted to planted pine after harvest. Conversely, however, many harvested pine plantations revert to other forest types, mainly due to passive regeneration behavior on nonindustrial private timberlands. We model land use and land cover changes as a basis for projecting future changes in planted pine area, to aid policy analysts concerned with mitigation activities for global climate change. Projections are prepared in two stages. Projected land use changes include deforestation due to pressures to develop rural land as the human population expands, which is a larger area than that converted from other rural lands (e.g., agriculture) to forestry. In the second stage, transitions among forest types are projected on land allocated to forestry. We consider reforestation, influences of timber harvest, and natural succession and disturbance processes. Baseline projections indicate a net increase of about 5.6 million ha in planted pine area in the South over the next 50 years, with a notable increase in sequestered carbon. Additional opportunities to expand pine plantation area warrant study of landowner behavior to aid in designing more effective incentives for inducing land use and land cover changes to help mitigate climate change and attain other goals.  相似文献   

19.
During the early 1930's, more than 340,000 acres of abandoned farmland in New York State were purchased by the State Conservation Department for the planting, growing, and harvesting of trees. Since then, this land has developed from a heavy cover of weeds and brush into dense coniferous woodlands with trees averaging well over 30 feet high. Hydrologic data have been collected since 1932 in Central New York to determine the effect of the reforestation on streamflow. Data are available for three small partly reforested areas and for one non-reforested control area. Intensive statistical analyses of the data from the four study areas were made in 1958. It was determined at that time that significant reductions in total runoff had occurred which were attributed to increases in interception and transpiration. Reductions in peak discharges during the dormant season also were indicated which were attributed to increased interception and sublimation of snowfall, and gradual desynchronization of snowmelt runoff from the wooded and open areas of partly reforested watersheds. Updating of the studies relating to peak discharges was completed in 1967 and indicated that no further changes in relative peaks had taken place since 1958. From this it is concluded that the influence exerted by the forest had become maximum by 1958 and has remained stable since then.  相似文献   

20.
Lakes,Wetlands, and Streams as Predictors of Land Use/Cover Distribution   总被引:2,自引:0,他引:2  
The importance of the surrounding landscape to aquatic ecosystems has been well established. Most research linking aquatic ecosystems to landscapes has focused on the one-way effect of land on water. However, to understand fully the complex interactions between aquatic and terrestrial ecosystems, aquatic ecosystems must be seen not only as receptors of human modification of the landscape, but also as potential drivers of these modifications. We hypothesized that the presence of aquatic ecosystems influences the spatial distribution of human land use/cover of the nearby landscape (≤1 km) and that this influence has changed through time from the 1930s to the 1990s. To test this hypothesis, we compared the distribution of residential, agricultural, and forested land use/cover around aquatic ecosystems (lakes, wetlands, and streams) to the overall regional land use/cover proportion in an area in southeast Michigan, USA; we also compared the distribution of land use/cover around county roads/highway and towns (known determinants of many land use/cover patterns) to the regional proportion. We found that lakes, wetlands, and streams were strongly associated with the distribution of land use/cover, that each ecosystem type showed different patterns, and that the magnitude of the association was at least as strong as the association with human features. We also found that the area closest to aquatic ecosystems (<500 m) was more strongly associated with land use/cover distribution than areas further away. Finally, we found that the strength of the association between aquatic ecosystems and land use/cover increased from 1938 to 1995, although the overall patterns were similar through time. Our results show that a more complete understanding is needed of the role of aquatic ecosystems on the distribution of land use/cover.  相似文献   

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