黄土高原典型区植被恢复及其对生态系统服务的影响

摘要

植被恢复是全球陆地生态系统恢复的主要途径,我国的大规模植被恢复具有特色,产生了巨大效益和广泛影响.退耕还林(草)是我国重大植被恢复工程的典型代表,在黄土高原地区试验示范进而推广到全国.工程实施以来,工程区植被的恢复情况及其产生的影响已成为学术界关注的热点.选取陕西省延安市、榆林市和山西省吕梁市、临汾市作为黄土高原典型区,分析了土地利用变化情况.基于2000-2014年的年均植被覆盖度数据分析了植被恢复的时空变化趋势.在此基础上,以土壤侵蚀率、地表植被蒸散(ET)和植被净初级生产力(NPP)为指标,对典型区土壤保持服务、水文调节服务和植被碳固定服务的变化进行定量评估,以此分析植被恢复对主要生态系统服务的作用.结果显示:(1)工程实施以来林地和草地范围明显增加.(2)植被改善趋势明显,2000-2005、2000-2010和2000-2014年植被显著恢复的比例分别为5.8％、49.1％和79.0％.(3)土壤保持服务增强,2014年土壤侵蚀速率比2000年降低17.5％,中度侵蚀区降幅达53.7％,2000-2014年历年土壤保持率均在84％以上且呈波动增加.(4)水文调节服务增强,2000-2010年ET增加区域面积达到48 094.1 km2,占典型区总面积的39.6％.(5)植被碳固定服务提高,2000-2014年典型区NPP总体处于增加态势,NPP显著增加区域占全区总面积的60.3％,固碳总量增加45.4％.研究表明,退耕还林(草)工程实施以来,典型区植被得到了显著恢复,有效促进了区域生态系统服务的提高,植被恢复及其生态系统服务效应的时空变异特征值得关注.%Restoring vegetation is the main approach to remediation of the global ecosystem.In China,the large scale vegetation rehabilitation activities are distinctive ecological measures,which have brought about enormous benefits and wide implications for the ecological remediation process.As a typical example of the great vegetation rehabilitation programs,the “Grain for Green Program” (GFGP) was initiated and experimented in the Loess Plateau as demonstration,and extrapolated nationwide.Since the implementation of GFGP,how the vegetation restoration was going on and what its implications were have become a hot spot in the academic circle.Implementations of the GFGP in Yan'an and Yulin Cities of Shaanxi Province,and Lüliang and Linfen Cities of Shanxi Province,typical areas of the Loess Plateau,were surveyed and changes in land use analyzed.Based on the data of annual mean vegetation coverage in 2000-2014,spatio-temporal changes of the vegetation were characterized.On such a basis,ecosystem services,such as soil conservation service,hydrological regulation service and vegetation carbon sequestration service in these typical areas were evaluated quantitatively,using soil erosion rate,surface vegetation evapotranspiration (ET) and vegetation net primary productivity (NPP) as indexes,so as to analyze effects of the vegetation restoration on major ecosystem services.Results show:(1) The areas of forests and grasslands have increased significantly since the implementation of GFGP;(2) These areas as a whole improved significantly in vegetation coverage with the years passing on.The area of newly restored vegetation accounted for 5.8％,49.1％ and 79.0％ in 2000-2005,2000-2010 and 2000-2014,respectively;(3) The soil conservation service strengthened,thus reducing the soil erosion rate by 17.5％ from 1 162.6 t · km-2 · a-1 in 2000 to 959.6 t · km-2 · a-1 in 2014 and the area of moderate erosion by 53.7％,and keeping the soil conservation rate well above 84％ and on a fluctuating and rising trend;(4) The hydrological regulation service improvement.The area with increased ET reached 48 094.1 km2,or 39.6％ of the total land area of the four cities;and (5) The carbon sequestration service heightened,with NPP generally on a rising trend.The areas with significantly increased NPP accounted for 60.3％ of the total land area of the four cities.Total carbon sequestration increased by 45.4％ from 39.2 Tg in 2000 to 57.0 Tg in 2014.This study revealed that the implementatian of GFGP has significantly improved the vegetation in the studied areas,thus greatly strengthening ecosystem services in the region.Spatio-temporal variation of vegetation restoration and its effects on ecosystem service should draw more attention from both scientists and decision makers.