Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoige Plateau on the Qinghai-Tibet Plateau was used as a research site f...Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoige Plateau on the Qinghai-Tibet Plateau was used as a research site for research on alpine wetland delineation. Several studies have analyzed the spatiotemporal pattern and dynamics of these alpine wetlands, but none have addressed the issues of wetland boundaries. The objective of this work was to discriminate the upper boundaries of alpine wetlands by coupling ecological methods and satellite observations. The combination of Landsat 8 images and supervised classification was an effective method for rapid identification of alpine wetlands in the Zoig6 Plateau. Wet meadow was relatively stable compared with hydric soils and wetland hydrology and could be used as a primary indicator for discriminating the upper boundaries of alpine wetlands. A slope of less than 4.5° could be used as the threshold value for wetland delineation. The normalized difference vegetation index （NDVI） in 434 field sites showed that a threshold value of 0.3 could distinguish grasslands from emergent marsh and wet meadow in September. The median normalized difference water index （NDWI） of emergent marsh remained more stable than that of wet meadow and grasslands during the period from September until July of the following year. The index of mean density in wet meadow zones was higher than the emergent and upland zones. Over twice the number of species occurred in the wet meadow zone compared with the emergent zone, and close to the value of upland zone. Alpine wetlands in the three reserves in 2014 covered 1175.19 kin2 with a classification accuracy of 75.6%. The combination of ecological methods and remote sensing technology will play an important role in wetland delineation at medium and small scales. The correct differentiation between wet meadow and grasslands is the key to improving the accuracy of future wetland delineation.展开更多
vegetation continuous The scale-location specific control on distribution was investigated through wavelet transforms approaches in subtropical mountain-hill region, Fujian, China. The Normalized Difference Vegetatio...vegetation continuous The scale-location specific control on distribution was investigated through wavelet transforms approaches in subtropical mountain-hill region, Fujian, China. The Normalized Difference Vegetation Index （NDVI） was calculated as an indicator of vegetation greenness using Chinese Environmental Disaster Reduction Satellite images along latitudinal and longitudinal transects. Four scales of variations were identified from the local wavelet spectrum of NDVI, with much stronger wavelet variances observed at larger scales. The characteristic scale of vegetation distribution within mountainous and hilly regions in Southeast China was around 20 km. Significantly strong wavelet coherency was generally examined in regions with very diverse topography, typically characterized as small mountains and hills fractured by rivers and residents. The continuous wavelet based approaches provided valuable insight on the hierarchical structure and its corresponding characteristic scales of ecosystems, which might be applied in defining proper levels in multilevel models and optimal bandwidths in Geographically Weighted Regression.展开更多
The influences of interannual variability of vegetation LAI on surface temperature are investigated via two ensemble simulations, applying the Community Earth System Model. The interannual LAI, derived from Global Inv...The influences of interannual variability of vegetation LAI on surface temperature are investigated via two ensemble simulations, applying the Community Earth System Model. The interannual LAI, derived from Global Inventory Modeling and Mapping Studies NDVI for the period 1982-2011, and its associated climatological LAI, are used in the two ensemble simulations, respectively.The results show that the signals of the influences, represented as ensemble-mean differences, are generally weaker than the noises of the atmospheric variability, represented as one standard deviation of the ensemble differences. Spatially, the signals are stronger over the tropics compared with the mid-high latitudes. Such stronger signals are contributed by the significant linearity between LAI and surface temperature, which is mainly caused via the influences of LAI on evapotranspiration.The maximum amplitudes of the influences on the interannual variability of surface temperature are high and thus deserve full consideration. However, the mean magnitudes of influences are small because of the small changes in the amplitudes of LAI. This work only investigates the influences of the interannual variability of LAI and does not consider interannual changes in other vegetation characteristics, such as canopy height and fractional cover. Further work involving dynamic vegetation models may be needed to investigate the influences of vegetation variability.展开更多
基金Under the auspices of National Natural Science Foundation of China(No.41201445,41103041)National Science and Technology Support Program(No.2012BAJ24B01)National High Technology Research and Development Program of China(No.2009AA12200307)
文摘Accurate wetland delineation is the basis of wetland definition and mapping, and is of great importance for wetland management and research. The Zoige Plateau on the Qinghai-Tibet Plateau was used as a research site for research on alpine wetland delineation. Several studies have analyzed the spatiotemporal pattern and dynamics of these alpine wetlands, but none have addressed the issues of wetland boundaries. The objective of this work was to discriminate the upper boundaries of alpine wetlands by coupling ecological methods and satellite observations. The combination of Landsat 8 images and supervised classification was an effective method for rapid identification of alpine wetlands in the Zoig6 Plateau. Wet meadow was relatively stable compared with hydric soils and wetland hydrology and could be used as a primary indicator for discriminating the upper boundaries of alpine wetlands. A slope of less than 4.5° could be used as the threshold value for wetland delineation. The normalized difference vegetation index （NDVI） in 434 field sites showed that a threshold value of 0.3 could distinguish grasslands from emergent marsh and wet meadow in September. The median normalized difference water index （NDWI） of emergent marsh remained more stable than that of wet meadow and grasslands during the period from September until July of the following year. The index of mean density in wet meadow zones was higher than the emergent and upland zones. Over twice the number of species occurred in the wet meadow zone compared with the emergent zone, and close to the value of upland zone. Alpine wetlands in the three reserves in 2014 covered 1175.19 kin2 with a classification accuracy of 75.6%. The combination of ecological methods and remote sensing technology will play an important role in wetland delineation at medium and small scales. The correct differentiation between wet meadow and grasslands is the key to improving the accuracy of future wetland delineation.
基金supported by the National Natural Science Foundation of China(NSFC)(Grant No.41071267)Scientific Research Foundation for Returned Scholars,Ministry of Education of China(Grant No.[2012]940)the Science & Technology Department of Fujian Province,China(Grant Nos.2012I0005,2012J01167)
文摘vegetation continuous The scale-location specific control on distribution was investigated through wavelet transforms approaches in subtropical mountain-hill region, Fujian, China. The Normalized Difference Vegetation Index （NDVI） was calculated as an indicator of vegetation greenness using Chinese Environmental Disaster Reduction Satellite images along latitudinal and longitudinal transects. Four scales of variations were identified from the local wavelet spectrum of NDVI, with much stronger wavelet variances observed at larger scales. The characteristic scale of vegetation distribution within mountainous and hilly regions in Southeast China was around 20 km. Significantly strong wavelet coherency was generally examined in regions with very diverse topography, typically characterized as small mountains and hills fractured by rivers and residents. The continuous wavelet based approaches provided valuable insight on the hierarchical structure and its corresponding characteristic scales of ecosystems, which might be applied in defining proper levels in multilevel models and optimal bandwidths in Geographically Weighted Regression.
基金supported by the major research projects of the National Natural Science Foundation of China[grant number91230202]
文摘The influences of interannual variability of vegetation LAI on surface temperature are investigated via two ensemble simulations, applying the Community Earth System Model. The interannual LAI, derived from Global Inventory Modeling and Mapping Studies NDVI for the period 1982-2011, and its associated climatological LAI, are used in the two ensemble simulations, respectively.The results show that the signals of the influences, represented as ensemble-mean differences, are generally weaker than the noises of the atmospheric variability, represented as one standard deviation of the ensemble differences. Spatially, the signals are stronger over the tropics compared with the mid-high latitudes. Such stronger signals are contributed by the significant linearity between LAI and surface temperature, which is mainly caused via the influences of LAI on evapotranspiration.The maximum amplitudes of the influences on the interannual variability of surface temperature are high and thus deserve full consideration. However, the mean magnitudes of influences are small because of the small changes in the amplitudes of LAI. This work only investigates the influences of the interannual variability of LAI and does not consider interannual changes in other vegetation characteristics, such as canopy height and fractional cover. Further work involving dynamic vegetation models may be needed to investigate the influences of vegetation variability.
