| Vegetation phenology is one of the important indicators reflecting the current growth of vegetation and climate and environmental changes.In recent years,the research on the response of vegetation phenology and primary productivity to meteorological factors has become the focus of research in geography,environment and ecology.As one of the“five pastoral areas”in China,Xinjiang's grassland ecological environment development will not only directly affect the development of local animal husbandry,but also affect local ecological security.For the fragile ecosystems in Xinjiang and the deteriorating ecological environment,the study of grassland phenology and net primary productivity of grassland will prompt us to understand more about the current status and trends of grassland in Xinjiang.Studying the relationship between grassland phenology and grassland net primary productivity in Xinjiang has important scientific and practical significance for the protection and rational use of natural grassland resources in Xinjiang.Based on MODIS NDVI data and temperature,precipitation and radiation data of meteorological sites,this study combined the Xinjiang grassland type,measured biomass data and Xinjiang elevation data to accurately estimate the net primary productivity of Xinjiang grassland using CASA model.The spatial and temporal distribution patterns of net primary productivity of different grassland types in Xinjiang were analyzed.In addition,using the 2001-2014 MCD12Q2 dataset,the three main parameters of grassland phenology in Xinjiang are extracted from the continuous time series data.The parameters include:growth season start date(SOS),growing season length(LOS),and growing season.End date(EOS).Then the spatial and temporal distribution changes and interannual variation trends of grassland phenological parameters in Xinjiang were analyzed and explored,and the extracted phenological parameters were correlated with grassland NPP to study the impact of grassland phenology on NPP in Xinjiang.Through the above three aspects of research,the preliminary conclusions of this paper are as follows:(1)The research on NPP in Xinjiang grassland found that the annual average variation of NPP in Xinjiang grassland was large.The annual average NPP of the whole Xinjiang region is 158 g C/(m2·a).From the spatial point of view,the northern Xinjiang part and the Ili valley area have the largest value,while the southern part of Xinjiang has the smallest value.According to the statistical analysis of the annual average NPP of different grassland types in Xinjiang,the annual average net primary productivity is ranked according to the distribution of grassland types:meadow?alpine subalpine meadow?plain grassland?alpine subalpine grassland?In the desert grassland,the NPP values of the grassland are:189 g C/(m~2·a),148 g C/(m~2·a),126 g C/(m~2·a),115 g C/(m~2·a),60 g C/(m~2·a).From the area of NPP distribution of different grassland types in Xinjiang,the area occupied by different grassland types is also quite different.Among them,the area of desert grassland distribution accounts for 35.32%of the total grassland area in Xinjiang.Plain grassland accounts for 14.48%of the area.The area of alpine subalpine meadows accounts for 7.93%of the area.The area of the meadow is25.02%of the total grassland area in Xinjiang.The area of alpine subalpine grassland accounts for 17.25%of the total grassland area in Xinjiang.(2)In the study of the spatial and temporal distribution changes and multi-year trends of different phenological parameters in Xinjiang from 2001 to 2014,it is found that the spatial and temporal variation patterns and multi-year trends of different phenological parameters are different.The distribution time of the beginning of the growing season of grassland phenology in Xinjiang is 73-154 days per year.Among the changes of the beginning of the growing season of grassland phenology,most of the areas show an early trend,and the area with slight advance is the largest;Xinjiang The length of the growing season of grassland phenology is 156~183d in one year.In the area distribution of grassland phenology in Xinjiang for many years,the overall trend is shortened,and the proportion of lightly shortened area is the largest,accounting for grassland.Thetotal area of 35.95%,followed by the proportion of the total area is slightly extended;the end of the growing season of Xinjiang grassland phenology is concentrated in the year of 241~317d,the end of the growing season of grassland phenology In the distribution of the area,the overall trend is basically unchanged.In the proportion of the area distribution at the end of the growing season,the area that is basically unchanged accounts for 42.08%of the grassland EOS in Xinjiang,followed by the delayed area.(3)The main parameters of different grassland types in Xinjiang have different effects on the annual average NPP,spring NPP,summer NPP and autumn NPP in Xinjiang.The research shows that the initial stage of the grassland phenological growth season in Xinjiang has the most significant effect on the NPP in spring,and the level between the two is extremely significant.However,the significance of the beginning of the grassland phenological growth season in Xinjiang and the other three NPPs is not obvious.The effects of the beginning of the growing season of plain grassland on summer NPP and autumn NPP reached a very significant level.The correlation between the beginning of the phenological growth season and the annual average NPP,summer NPP and autumn NPP was not obvious;Xinjiang grassland phenology length The effects of annual average NPP,spring NPP,summer NPP and autumn NPP did not reach significant levels;the correlation between the end of the grassland phenological growth season and the autumn NPP was most obvious,followed by the end of the phenological growth season of some grassland types in Xinjiang.The correlation of NPP is significant.However,the effects of different grassland phenological growth seasons on the NPP in summer and NPP in summer were not significant. |
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