Land use/land cover change (LUCC) mapping and analysis using multi-temporal normalize difference vegetation index (NDVI) data have been well documented. Recent empirical studies have documented that many new methods w...Land use/land cover change (LUCC) mapping and analysis using multi-temporal normalize difference vegetation index (NDVI) data have been well documented. Recent empirical studies have documented that many new methods with high accuracy of retrieved land surface temperature ( Ts) have been developed. Thus, the combination of land surface temperature and NDVI has the greatest potential to improve the surface vegetation dynamic monitoring. In this study, the following objectives are pursued to: (1) introduce the practical method to produce the Ts, NDVI and Ts/NDVI based on remotely sensed data; (2) investigate the different retrieved result of vegetation cover information from NDVI, Ts and Ts/NDVI data sets, and analyze the intra-annual time trajectories of different vegetation cover categories in the NDVI- Ts space for farming-pastoral zone in North China, and (3) quantitative analysis the difference in using NDVI, Ts and Ts/NDVI data sets to express information based on the indices (information entropy and averaged information grads), and evaluate the relative role of Ts/NDVI data set in the discrimination of different vegetation cover categories through comparison to traditional NDVI data set.展开更多
Accurate assessment of postfire vegetation recovery is important for forest management and the conservation of species diversity.Topography is an important factor aff ecting vegetation recovery but whether species com...Accurate assessment of postfire vegetation recovery is important for forest management and the conservation of species diversity.Topography is an important factor aff ecting vegetation recovery but whether species composition varies with diff erent recovery stages and between valleys and slopes is unclear.Using fi eld data and a space-for-time substitution method,we quantifi ed species richness and diversity to obtain the successional trajectories of valleys and slopes.We surveyed the species of 10 burned areas from 1986 to 2010 in the Greater Khingan Mountains in northeastern China,and found that with increasing postfi re recovery time,species richness in both valleys and slopes gradually decreased.However,species richness in valleys was relatively higher.Shrubs recovered rapidly in the valleys,and species diversity maximized approximately 11 years after fi re.However,it maximized 17–18 years after fi re on the slopes.Numerous shade-tolerant species were present in the valleys 11 years after fi re but not until after 18 years on slopes.Larch appeared earlier than 11 years after fi re and its recovery was slow in the valleys but appeared quickly on slopes and established dominance early.Our study provides some new insights into vegetation succession after fi re at local scales.After fi re,the vegetation recovery processes diff er with topography and it aff ects the initial rate of recovery and species composition at diff erent successional stages.展开更多
The Mongolian Plateau is one of the regions most sensitive to climate change,the more obvious increase of temperature in 21 st century here has been considered as one of the important causes of drought and desertifica...The Mongolian Plateau is one of the regions most sensitive to climate change,the more obvious increase of temperature in 21 st century here has been considered as one of the important causes of drought and desertification.It is very important to understand the multi-year variation and occurrence characteristics of drought in the Mongolian Plateau to explore the ecological environment and the response mechanism of surface materials to climate change.This study examines the spatio-temporal variations in drought and its frequency of occurrence in the Mongolian Plateau based on the Advanced Very High Resolution Radiometer(AVHRR)Normalized Difference Vegetation Index(NDVI)(1982–1999)and the Moderate-resolution Imaging Spectroradiometer(MODIS)(2000–2018)datasets;the Temperature Vegetation Dryness Index(TVDI)was used as a drought evaluation index.The results indicate that drought was widespread across the Mongolian Plateau between1982 and 2018,and aridification incremented in the 21 st century.Between 1982 and 2018,an area of 164.38×10^4 km^2/yr suffered from drought,accounting for approximately 55.28%of the total study area.An area of approximately 150.06×10^4 km^2(51.43%)was subject to more than 160 droughts during 259 months of the growing seasons between 1982 and 2018.We observed variable frequencies of drought occurrence depending on land cover/land use types.Drought predominantly occurred in bare land and grassland,both of which accounting for approximately 79.47%of the total study area.These terrains were characterized by low vegetation and scarce precipitation,which led to frequent and extreme drought events.We also noted significant differences between the areal distribution of drought,drought frequency,and degree of drought depending on the seasons.In spring,droughts were widespread,occurred with a high frequency,and were severe;in autumn,they were localized,frequent,and severe;whereas,in summer,droughts were the most widespread and frequent,but less severe.The increase in temperature,decrease in precipi展开更多
文摘Land use/land cover change (LUCC) mapping and analysis using multi-temporal normalize difference vegetation index (NDVI) data have been well documented. Recent empirical studies have documented that many new methods with high accuracy of retrieved land surface temperature ( Ts) have been developed. Thus, the combination of land surface temperature and NDVI has the greatest potential to improve the surface vegetation dynamic monitoring. In this study, the following objectives are pursued to: (1) introduce the practical method to produce the Ts, NDVI and Ts/NDVI based on remotely sensed data; (2) investigate the different retrieved result of vegetation cover information from NDVI, Ts and Ts/NDVI data sets, and analyze the intra-annual time trajectories of different vegetation cover categories in the NDVI- Ts space for farming-pastoral zone in North China, and (3) quantitative analysis the difference in using NDVI, Ts and Ts/NDVI data sets to express information based on the indices (information entropy and averaged information grads), and evaluate the relative role of Ts/NDVI data set in the discrimination of different vegetation cover categories through comparison to traditional NDVI data set.
基金funded by the National Natural Science Foundation of China(No.41871103).
文摘Accurate assessment of postfire vegetation recovery is important for forest management and the conservation of species diversity.Topography is an important factor aff ecting vegetation recovery but whether species composition varies with diff erent recovery stages and between valleys and slopes is unclear.Using fi eld data and a space-for-time substitution method,we quantifi ed species richness and diversity to obtain the successional trajectories of valleys and slopes.We surveyed the species of 10 burned areas from 1986 to 2010 in the Greater Khingan Mountains in northeastern China,and found that with increasing postfi re recovery time,species richness in both valleys and slopes gradually decreased.However,species richness in valleys was relatively higher.Shrubs recovered rapidly in the valleys,and species diversity maximized approximately 11 years after fi re.However,it maximized 17–18 years after fi re on the slopes.Numerous shade-tolerant species were present in the valleys 11 years after fi re but not until after 18 years on slopes.Larch appeared earlier than 11 years after fi re and its recovery was slow in the valleys but appeared quickly on slopes and established dominance early.Our study provides some new insights into vegetation succession after fi re at local scales.After fi re,the vegetation recovery processes diff er with topography and it aff ects the initial rate of recovery and species composition at diff erent successional stages.
基金Under the auspices of Special Project on Basic Resources of Science and Technology(No.2017FY101301)National Natural Science Foundation of China(No.41971398,31770764)Natural Science Foundation Balance Project(No.IDS2019JY-2)。
文摘The Mongolian Plateau is one of the regions most sensitive to climate change,the more obvious increase of temperature in 21 st century here has been considered as one of the important causes of drought and desertification.It is very important to understand the multi-year variation and occurrence characteristics of drought in the Mongolian Plateau to explore the ecological environment and the response mechanism of surface materials to climate change.This study examines the spatio-temporal variations in drought and its frequency of occurrence in the Mongolian Plateau based on the Advanced Very High Resolution Radiometer(AVHRR)Normalized Difference Vegetation Index(NDVI)(1982–1999)and the Moderate-resolution Imaging Spectroradiometer(MODIS)(2000–2018)datasets;the Temperature Vegetation Dryness Index(TVDI)was used as a drought evaluation index.The results indicate that drought was widespread across the Mongolian Plateau between1982 and 2018,and aridification incremented in the 21 st century.Between 1982 and 2018,an area of 164.38×10^4 km^2/yr suffered from drought,accounting for approximately 55.28%of the total study area.An area of approximately 150.06×10^4 km^2(51.43%)was subject to more than 160 droughts during 259 months of the growing seasons between 1982 and 2018.We observed variable frequencies of drought occurrence depending on land cover/land use types.Drought predominantly occurred in bare land and grassland,both of which accounting for approximately 79.47%of the total study area.These terrains were characterized by low vegetation and scarce precipitation,which led to frequent and extreme drought events.We also noted significant differences between the areal distribution of drought,drought frequency,and degree of drought depending on the seasons.In spring,droughts were widespread,occurred with a high frequency,and were severe;in autumn,they were localized,frequent,and severe;whereas,in summer,droughts were the most widespread and frequent,but less severe.The increase in temperature,decrease in precipi
