Sensitivity and areal differentiation of vegetation responses to hydrothermal dynamics on the northern and southern slopes of the Qinling Mountains in Shaanxi province

The Qinling Mountains,located at the junction of warm temperate and subtropical zones,serve as the boundary between north and south China.Exploring the sensitivity of the response of vegetation there to hydrothermal dynamics elucidates the dynamics and mechanisms of the main vegetation types in the context of changes in temperature and moisture.Importance should be attached to changes in vegetation in different climate zones.To reveal the sensitivity and areal differentiation of vegetation responses to hydrothermal dynamics,the spatio-temporal variation characteristics of the normalized vegetation index(NDVI)and the standardized precipitation evapotranspiration index(SPEI)on the northern and southern slopes of the Qinling Mountains from 2000 to 2018 are explored using the meteorological data of 32 meteorological stations and the MODIS NDVI datasets.The results show that:1)The overall vegetation coverage of the Qinling Mountains improved significantly from 2000 to 2018.The NDVI rise rate and area ratio on the southern slope were higher than those on the northern slope,and the vegetation on the southern slope improved more than that on the northern slope.The Qinling Mountains showed an insignificant humidification trend.The humidification rate and humidification area of the northern slope were greater than those on the southern slope.2)Vegetation on the northern slope of the Qinling Mountains was more sensitive to hydrothermal dynamics than that on the southern slope.Vegetation was most sensitive to hydrothermal dynamics from March to June on the northern slope,and from March to May(spring)on the southern slope.The vegetation on the northern and southern slopes was mainly affected by hydrothermal dynamics on a scale of 3–7 months,responding weakly to hydrothermal dynamics on a scale of 11–12 months.3)Some 90.34%of NDVI and SPEI was positively correlated in the Qinling Mountains.Spring humidification in most parts of the study area promoted the growth of vegetation all the year round.The sensitivity of vegetation responses to hydrothermal dynamics with increasing altitude increased first and then decreased.Elevations of 800 to 1200 m were the most sensitive range for vegetation response to hydrothermal dynamics.The sensitivity of the vegetation response at elevations of 1200–3000 m decreased with increasing altitude.As regards to vegetation type,grass was most sensitive to hydrothermal dynamics on both the northern and southern slopes of the Qinling Mountains;but most other vegetation types on the northern slope were more sensitive to hydrothermal dynamics than those on the southern slope.