| Hengduan Mountain area,which is acting as the essential ecological barrier for the upper reaches of the Yangtze River,exerts profound influences to the climate and ecological environment of its surrounding areas as well as the Middle West part of our country.As the core content of carbon budgets and climate change research,net primary productivity(NPP)is a crucial indicator to measure the health status and sustainable development level of ecosystem.Base on Spot Vegetation data set,1:1000000 vegetation types,temperature,precipitation,and topography data,we estimate the yearly and monthly NPP of Hengduan Mountain area from 2000-2014 through CASA model.Then,we analyze the spatiotemporal pattern,change rules and driving forces of NPP in Hengduan Mountain area through grid analysis,trend analysis,and correlation analysis methods.Main conclusions are as follows:(1)Total NPP presented an increasing trend from 2000 to 2014 in Hengduan Mountain area,its average total and annual value was 217.274 TgC and 486 gC·m-2·a-1,respectively.Among them,NPP was significantly increased from 2000 to 2008,with 3.647 TgC every year.However,NPP declined with the annual loss of 3.179 TgC from 2008 to 2014.Monthly NPP changes curve of Hengduan Mountain area was similar on the whole,but with a slight difference on the local.NPP began to rapidly accumulate carbon after April,and in July reached the peak.Then,accumulation rate declined,and the process ended in October.(2)On the whole,annual NPP was showing an increasing trend with distinct local disparity,ranging from-60 to 130 gC·m-2·a-1.Areas with significant increase in NPP were located in central Hengduan Mountain area,and high altitude regions of the Southern part,including Nujiang Gorge,Shaluli mountain,Snow mountain,Gongga mountain,Boxing and Tianquan county.Areas with significant decrease in NPP were located in Chaya county andGongjue county of southern Tibet,Wenchuan county and Heqing county of western Sichuan province,and the river valley in Jinsha River basin(Dali,Midu,Binchuan,Xiangyun,Panzhihua,and Yongren).(3)Average NPP of different vegetation ecosystem showed a significant gradient change in Hengduan Mountain area.Trees and grass were with the highest annual NPP of more than 750 gC · m-2 · a-1.Followed by grassland,cultivated vegetation and swamp,their annual NPP was between 500 and 650 gC · m-2 · a-1.Then,it was meadow,coniferous forest and shrub,their annual NPP was between 350 and 450 gC · m-2 · a-1.The lowest was alpine vegetation,its annual NPP was 240 gC · m-2 · a-1.From the contribution proportion to total NPP of different vegetation,shrub was larger than conifer forest,meadow,broad-leaved forest,grass,cultivated vegetation,alpine vegetation,and other vegetation types.The contribution rate of the first four vegetation to total NPP accounted for 78.91%.(4)Under the test level of F0.1,regions with NPP changes resulted from climatic factors took up 6.87 % of the total study area.These regions mainly sat at central Hengduan Mountain area,including Chaya county,Gongjue county and Shaluli Mountain,and Jinshajiang river valley of the southern part,including Binchuan county,Panzhihua city,Huili county and Yuanmou county.By contrast,those regions subjecting to non-climatic factors occupied for 93.13% of the whole area.And they were mainly located at the valley of central and southern part ofHengduan mountain area,Wenchuan county and low-elevation part of eastern edge of Hengduan mountain area. |
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