| Vegetation dynamic is a key process which was able to present the response of ecology system to climate change.As a sensitive area of climate change,the Qinghai-Tibet Plateau is known as"the driver and amplifier of global climate change".The study of vegetation dynamics in the Qinghai-Tibet Plateau provides important early warning information for assessing the response trend of global vegetation composition and ecological function to climate change,it also provides scientific reference and decision-making basis for the ecological security and sustainable development of agriculture,forestry,grassland and animal husbandry.However,the relationship between climate change and temporal variability of vegetation as well as the effect of climate on the spatial distribution pattern of vegetation in Qinghai-Tibet Plateau have not been quantified yet.This study obtained the vegetation information?including Normalized Difference Vegetation Index and vegetation types?and climate data?including annual climate data and mean annual climate data?of the Qinghai-Tibet Plateau based on remote sensing information,field survey and meteorological station data,respectively.And using mathematical model and statistical method,such as generalized additive model,boosted regression tree,structural equation model and changepoint detection mathematical model and statistical method,analyzed the influence of climate on time variability and spatial pattern of vegetation from the aspects of time and space.The results revealed the general rules of vegetation sensitivity to precipitation?VSP?,vegetation sensitivity to temperature?VST?over time,and the division rules of perennial average climate on vegetation pattern over space.It also quantified the hydrothermal conditions under the changes of VSP and VST,as well as the threshold of climate under the changes of vegetation pattern.The main conclusions are as follows:?1?In general,from 1982 to 2013,NDVI on the Qinghai-Tibet Plateau showed a downward trend,while the temperature and precipitation showed an increasing tendency.However,the NDVI is positively correlated with the precipitation and temperature.?2?Both of the VSP and VST are significantly different in different seasons,with VSP was the highest in summer,while the peak value of VST was found in spring.And from 1982 to 2013,VSP was gradually strengthened in spring and winter,while VST was gradually weakened in summer,and the VSP and VST in other seasons did not changed significantly.?3?The threshold hydrothermal conditions for significant changes in VSP and VST are 4 mm-12 mm and 0°C,respectively.And the climate change under the threshold hydrothermal conditions above is the main reason for significant changes of VSP in spring and winter and VST in summer.?4?The mean annual solar radiation?SR?,mean annual precipitation?MAP?and mean annual water vapor pressure?WVP?are the main climate drivers affecting vegetation patterns.The climatic thresholds for the transition between different vegetation ecosystems are 184000 k J?m-2?d-1?SR?,440 mm?MAP?and 3.7 k Pa?WVP?,respectively.?5?On the Qinghai-Tibet Plateau,the precipitation,solar radiation and water vapor pressure were regulated by longitude,latitude and altitude,respectively.In fact,the transition between different vegetation ecosystems is the change of corresponding climate environment in space. |
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