秦岭陕西段南北坡植被对干湿变化响应敏感性及空间差异

秦岭位于暖温带与亚热带交界处,也是中国南北地理分界线,秦岭南北坡植被对干湿变化响应敏感性,可以折射出暖温带、亚热带地区主要植被类型对干湿变化的响应规律和机制特征,对深入理解不同气候带植被变化规律具有重要意义。本文利用秦岭山地32个气象站点的气象数据和MODIS NDVI时间序列数据集,探讨了2000—2018年秦岭南北坡NDVI和SPEI时空变化特征,揭示了南北坡植被对干湿变化响应敏感性及其空间差异。结果表明：① 2000—2018年秦岭植被覆盖情况整体显著改善,但秦岭南坡NDVI上升幅度和面积占比均高于北坡,南坡植被比北坡改善情况好。秦岭湿润化趋势不显著,但秦岭北坡湿润化速率和面积占比均大于南坡。② 秦岭北坡植被比南坡植被更易受干湿变化影响,秦岭北坡植被对3—6月总体干湿变化最为敏感,南坡植被对3—5月（春季）干湿变化最为敏感。秦岭南北坡植被主要受3~7个月尺度干湿变化影响,对11~12个月尺度的干湿变化响应较弱。③ 秦岭有90.34%的区域NDVI与SPEI呈正相关,大部分地区春季湿润化能促进全年植被生长;随海拔上升,植被对干湿变化响应敏感性先上升再下降,海拔800~1200 m是植被响应最敏感的海拔段,海拔1200~3000 m随海拔上升植被响应敏感性下降;南北坡草丛均是对干湿变化响应最为敏感的植被类型,但秦岭北坡多数植被类型对干湿变化响应比南坡敏感。

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

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.