In order to assess the climatical and ecological effect which returned the farmland to pasture or forest, the vegetation and crop in Northwest China with suitable threshold value were classified in this experiment by ...In order to assess the climatical and ecological effect which returned the farmland to pasture or forest, the vegetation and crop in Northwest China with suitable threshold value were classified in this experiment by using multi-temporal SPOT/VEGETATION dada and combing supervised classification with unsupervised classification. Compared with the data from Statistical Department and actual investigation, the precision of the classified result was above 85%.展开更多
This study aims to provide a predictive vegetation mapping approach based on the spectral data, DEM and Generalized Additive Models (GAMs). GAMs were used as a prediction tool to describe the relationship between vege...This study aims to provide a predictive vegetation mapping approach based on the spectral data, DEM and Generalized Additive Models (GAMs). GAMs were used as a prediction tool to describe the relationship between vegetation and environmental variables, as well as spectral variables. Based on the fitted GAMs model, probability map of species occurrence was generated and then vegetation type of each grid was defined according to the probability of species occurrence. Deviance analysis was employed to test the goodness of curve fitting and drop contribution calculation was used to evaluate the contribution of each predictor in the fitted GAMs models. Area under curve (AUC) of Receiver Operating Characteristic (ROC) curve was employed to assess the results maps of probability. The results showed that: 1) AUC values of the fitted GAMs models are very high which proves that integrating spectral data and environmental variables based on the GAMs is a feasible way to map the vegetation. 2) Prediction accuracy varies with plant community, and community with dense cover is better predicted than sparse plant community. 3) Both spectral variables and environmental variables play an important role in mapping the vegetation. However, the contribution of the same predictor in the GAMs models for different plant communities is different. 4) Insufficient resolution of spectral data, environmental data and confounding effects of land use and other variables which are not closely related to the environmental conditions are the major causes of imprecision.展开更多
Vegetation plays a significant role in global terrestrial ecosystems and in combating desertification.We analyzed vegeta tion change in Inner Mongolia of northern China using the Normalized Difference Vegetation Index...Vegetation plays a significant role in global terrestrial ecosystems and in combating desertification.We analyzed vegeta tion change in Inner Mongolia of northern China using the Normalized Difference Vegetation Index(NDVI)from 1998 to 2013,which is an important composite of Chinese National Ecological Security Shelter.The correlation between vegeta tion growth and drought quantified using the Standardized Precipitation Evapotranspiration Index(SPEI)was also ex plored.Results show that vegetation in most of the study area has been rehabilitated to various degrees,especially in re gions such as most of the Horqin Sandy Land,eastern Ordos Plateau,Hetao Plain,as well as the middle-northern Da Hing gan Ling Mountains.Vegetation improvement in spring was significant in most of the study area.Vegetation degradation was centrally distributed in Xilingol grassland close to the Sino-Mongolia border and abandoned croplands in Ulanqab Meng.Vegetation change trends and seasonal differences varied among different vegetation types.The biggest vegetation variation in the growing season was the belt-like distribution along those grasslands close to the precipitation isoline of 200 mm and the Sino-Mongolia border,but also variation in summer and autumn exist in obvious spatial differences be tween grasslands and forests.Drought largely influenced vegetation change of Inner Mongolia at 6-month scale or 12-month scale,except for forests of eastern Hunlun Buir Meng and deserts or gobi deserts of western Alxa Meng.Moreover,drought in the previous winter and early spring seasons had a lag effect on growing-season vegetation.Desert grassland was the most easily affected by drought in the study area.Anthropogenic activities have made great progress in improving local vegetation under the lasting drought background.展开更多
基金Supported by the National Natural Science Foundation of China(No.40675071)~~
文摘In order to assess the climatical and ecological effect which returned the farmland to pasture or forest, the vegetation and crop in Northwest China with suitable threshold value were classified in this experiment by using multi-temporal SPOT/VEGETATION dada and combing supervised classification with unsupervised classification. Compared with the data from Statistical Department and actual investigation, the precision of the classified result was above 85%.
基金Under the auspices of National Natural Science Foundation of China(No.41001363)
文摘This study aims to provide a predictive vegetation mapping approach based on the spectral data, DEM and Generalized Additive Models (GAMs). GAMs were used as a prediction tool to describe the relationship between vegetation and environmental variables, as well as spectral variables. Based on the fitted GAMs model, probability map of species occurrence was generated and then vegetation type of each grid was defined according to the probability of species occurrence. Deviance analysis was employed to test the goodness of curve fitting and drop contribution calculation was used to evaluate the contribution of each predictor in the fitted GAMs models. Area under curve (AUC) of Receiver Operating Characteristic (ROC) curve was employed to assess the results maps of probability. The results showed that: 1) AUC values of the fitted GAMs models are very high which proves that integrating spectral data and environmental variables based on the GAMs is a feasible way to map the vegetation. 2) Prediction accuracy varies with plant community, and community with dense cover is better predicted than sparse plant community. 3) Both spectral variables and environmental variables play an important role in mapping the vegetation. However, the contribution of the same predictor in the GAMs models for different plant communities is different. 4) Insufficient resolution of spectral data, environmental data and confounding effects of land use and other variables which are not closely related to the environmental conditions are the major causes of imprecision.
基金supported by the Project of National Key Research and Development Program of China (Grant number 2016YFC0500902)the National Natural Science Foundation of China (Grant number 40801003)the National Basic Research Program of China (Grant number 2009CB421308)
文摘Vegetation plays a significant role in global terrestrial ecosystems and in combating desertification.We analyzed vegeta tion change in Inner Mongolia of northern China using the Normalized Difference Vegetation Index(NDVI)from 1998 to 2013,which is an important composite of Chinese National Ecological Security Shelter.The correlation between vegeta tion growth and drought quantified using the Standardized Precipitation Evapotranspiration Index(SPEI)was also ex plored.Results show that vegetation in most of the study area has been rehabilitated to various degrees,especially in re gions such as most of the Horqin Sandy Land,eastern Ordos Plateau,Hetao Plain,as well as the middle-northern Da Hing gan Ling Mountains.Vegetation improvement in spring was significant in most of the study area.Vegetation degradation was centrally distributed in Xilingol grassland close to the Sino-Mongolia border and abandoned croplands in Ulanqab Meng.Vegetation change trends and seasonal differences varied among different vegetation types.The biggest vegetation variation in the growing season was the belt-like distribution along those grasslands close to the precipitation isoline of 200 mm and the Sino-Mongolia border,but also variation in summer and autumn exist in obvious spatial differences be tween grasslands and forests.Drought largely influenced vegetation change of Inner Mongolia at 6-month scale or 12-month scale,except for forests of eastern Hunlun Buir Meng and deserts or gobi deserts of western Alxa Meng.Moreover,drought in the previous winter and early spring seasons had a lag effect on growing-season vegetation.Desert grassland was the most easily affected by drought in the study area.Anthropogenic activities have made great progress in improving local vegetation under the lasting drought background.
