| Karst areas have become one of the most typical fragile ecological areas in China.Affected by climate change and human activities,the regional ecological environment is facing severe threats and challenges.Studying the growth status of forests in this region and their correlation with climate change and land use can help reveal the effects and mechanisms of vegetation types on climate change in karst areas of China under the background of global warming,and quantify the pros and cons of human activities on the net primary productivity of forest ecosystems.Net primary productivity(NPP)of forest ecosystem,which is a vital basis for understanding the carbon budget of forest ecosystem,is an important indicator of forest ecosystem resource management and sustainable development.Based on remote sensing data,meteorological data and other data,this thesis utilize CASA model to estimate the forest NPP of Guizhou Province from 2000 to 2020,uses correlation analysis,spatial analysis and other analytical methods to study the spatiotemporal change characteristics of forest NPP across 21 years,and quantitatively evaluates the relative impact of climate change and land use change on forest NPP in this region.The main conclusions are as follows:(1)From 2000 to 2020,the average forest NPP in Guizhou Province was 538.22g C/m~2·a,and the overall trend of interannual change was gradually increasing.In the seasonal variation,the cumulative output of NPP in summer is the highest,reaching the peak in July(99.64±14.14 g C/m~2·a)and August(96.50±15.39 g C/m~2·a).(2)During the past 21 years,the overall forest NPP in Guizhou Province showed a spatial distribution pattern which presenting"high in the south and low in the north".Except for the small spatial difference in winter,the spatial distribution pattern among spring,summer and autumn showed a distribution characteristic of"high in the south and low in the north".Southwestern Guizhou Prefecture has the highest annual average of NPP(739.45±67.94 g C/m~2·a,Total NPP is 6.59±0.63 Tg),and Southeast Guizhou Prefecture has the highest total NPP(12.94±1.34 Tg,The annual average NPP is 522.39±52.28 g C/m~2·a).(3)The overall spatial fluctuation of forest NPP space in Guizhou Province is low,and most areas are stable.The trend of spatial change is mainly inapparent,showing a slight increase trend.The spatial pattern of Hurst index is high in the south and low in the north,suggesting it will show an increasing-weak anti sustained change in the future.(4)The climate in Guizhou tends to be warm and humid,and the forest NPP is positively correlated with temperature,precipitation and solar radiation.Through the analysis of geographical detectors,it is concluded that the interaction among those factors is shown as the enhanced interaction of two factors,and the strongest explanation of the interaction is the annual average temperature and solar radiation.(5)From 2000 to 2020,the proportion of forest area and construction land showed an increasing trend,the proportion of farmland area showed a trend of first increasing and then decreasing,and the proportion of grassland and shrub area showed a trend of decreasing.Forest is the main land use type in Guizhou Province,and the change of forest NPP is closely related to land use change.The loss of forest NPP is mainly related to the conversion of forest to other land use types,with the total loss of NPP from forest to farmland being 0.71 Tg C,and the total loss of NPP from forest to shrub being 0.12 Tg C;The increase is mainly related to the conversion of farmland and shrubs to forests,with the total increase of NPP from farmland to forest being 1.33 Tg C,and the total increase of NPP from shrubs to forest being 0.62 Tg C.Overall,the total NPP from farmland and shrubs to forests is the majority.Overall,the contribution of climate change to total forest NPP change(66.43%)is higher than that of land use change(31.68%). |
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