Quantitative Response Of Global Karst Vegetation To Drought-Stressed Climate

Since the beginning of this century,affected by climate change and land cover change caused by human activities,there has been a significant trend of vegetation greening on a global or national scale.However,there are still some terrestrial ecosystems in the world that are considered as fragile ecosystems and priority areas for ecological restoration,and have become key biomes for the study of global vegetation and climate change.As a widely distributed "dryland + mountain" dual ecological structure,karst has the characteristics of shallow soil layer,poor water conservation capacity and vegetation resilience,as a result,it is very prone to ecological degradation after climate change and human activities.It is also an ecosystem with great carbon sink potential and high ecological value,which has become the focus of national ecological evaluation and restoration.Global climate change and greenhouse gas emissions have not only aggravated global surface warming,but also exacerbated the frequency and intensity of extreme climate events.As the most widely distributed extreme climate event in the world,drought may cause permanent ecological degeneration to the fragile terrestrial ecosystem.However,drought stress varies with spatiotemporal patterns,the response of vegetation growth activities to short-term or long-term water deficits still lacks comprehensive and quantitative knowledge.Therefore,focusing on the response of karst vegetation to drought stress is of scientific significance to the assessment of fragile karst ecosystems under global climate change and the key ecological protection.In this paper,the following research work has been carried out in view of the main problems such as the unclear distinction of vegetation and water balance between different karst ecoregions in the world,the difficulty of quantifying the response of karst vegetation to water deficit,and the ambiguous growth and development stage of karst vegetation in southwestern China under global extreme climate:(1)According to the climate classification data and potential distribution of biomes,the global karst ecological zoning is carried out to find out the characteristics of hydrothermal elements,vegetation growth,water balance and their annual changes in various karst ecological areas around the world.Based on the global monthly and annual composited remote sensing imageries from 2001 to 2019,including LST,precipitation,NDVI,GPP,multi-scale meteorological drought index(SPEI and PDSI in 1-12 months),atmospheric VPD and three kinds of soil moisture data(ERA5,FLDAS and Terra Climate soil moisture),the inter-reaction and correlation of "Climate variables-Vegetation growth" in karst ecological area is studied,and the annual changes of drought stress caused by three types of water deficit were comprehensively analyzed.(2)The pixel-wise drought stress windows(DSW)and delayed vegetation response windows(DVRW)were quantified to analyze the regular pattern of vegetation response in global karst ecoregions to drought stress climate in recent 20 years.The results show that the global drought stress is significantly intensified,but the vegetation response in karst areas is obviously reduced.Through the analysis of the time scale,severity and response time of drought stress,it shows that the temperate karst forest has a strong response to short-term drought,but the long-term water restriction promotes the adaptability of plant physiological drought resistance,while the karst vegetation in the north of high latitude has a rapid and obvious response to the stress of sudden drought events.The results showed consistent conclusions under a variety of water balance indicators,demonstrating the interaction law between vegetation response and drought-stressed climate.(3)Based on the response mechanism and method of vegetation to drought stress,a comparative analysis of karst forest ecosystems developed at domestic and foreign was conducted,focusing on the vegetation growth status and ecosystem evaluation of karst vegetation in Southwest China under the global extreme climate.Karst areas in China are continuously affected by multiple restrictive environmental variables such as subtropical monsoonal hydrothermal erosion pressure,rugged and porous karst geological conditions,mosaic pattern of young forests and plantations,dense population and villages.Although China’s ecological engineering has brought rapid "greening" of vegetation under remote sensing monitoring,the vegetation has not developed to a mature and stable stage.The research shows that the problem of drought vulnerability in southwest karst area is still prominent,and there is not sufficiently resistant to extreme arid climates.Based on the quantitative response of vegetation to drought stress,this paper highlights the vulnerability of karst vegetation under the pressure of global drought stress and the importance of karst ecological restoration in Southwest China,which provides a scientific reference for the national solution to extreme climate change.