Abstract:

The Qinling Mountains, located at the junction of warm temperate and subtropical zones, serves as the boundary between North and South China. Exploring the sensitivity of vegetation response to hydrothermal dynamics can be conducive to understanding the pattern and dynamics of main vegetation types and the mechanism of their response to changes in temperature and moisture. Importance should be attached to the laws of vegetation change in different climate zones. To reveal the sensitivity and areal differentiation of vegetation responses to hydrothermal dynamics, the spatial and temporal variation characteristics of NDVI and SPEI on the southern and northern slopes of the Qinling Mountains from 2000 to 2018 are explored using the meteorological data from 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 exhibited better improvement 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, and it responds weakly to hydrothermal dynamics on a scale of 11-12 months. (3) 90.34% of NDVI and SPEI were positively correlated in the Qinling Mountains. Spring humidification in most parts of the study area could promote the growth of vegetation all the year round. The sensitivity of vegetation responses to hydrothermal dynamics with increasing altitude increased first and then decreased. The altitude of 800 to 1200 m was the most sensitive altitude for vegetation response to hydrothermal dynamics. The sensitivity of vegetation response at the elevation of 1200-3000 m decreased with the increasing altitude. The grass was the most sensitive vegetation type to hydrothermal dynamics on the northern and southern slopes of the Qinling Mountains, but most of other vegetation types on the northern slope were more sensitive to hydrothermal dynamics than those on the southern slope.

Key words: the Qinling Mountains in Shaanxi province, NDVI, SPEI, sensitivity, spatial difference