Simulation Study Of Climate Change Impacts On Vegetation Succession And Productivity In Tibetan Plateau

In recent years, all social circles have reached an agreement on climate change, which madeclimate and environmental factors changed and impacted natural ecosystems significantly in manyregions of the world. Tibetan Plateau is one of the most sensitive areas of climate change becauseof its unique geographical location and environment characteristics, and its climate condition andecological environment is with an important significance for Asia even the world. Therefore, toinvestigate the impacts of climate change on alpine ecosystems, especially the changes ofvegetation succession and net primary productivity, has a positive meaning on assessing theimpacts of climate change, drawing up the relevant adaptation strategies for protecting naturalecosystem of plateau, and promoting the sustainable development of local economic and sociallife.After a lot of debugging works, this research modified a dynamic global vegetation modelnamed LPJ to make it applicable to simulate in Tibetan Plateau. Then used historical climate datato drive the modified LPJ model simulating vegetation distribution and NPP （net primaryproductivity） pattern in Tibetan Plateau, and the results passed the accuracy verification. We usedregional climate model RegCM4.1to modeling1961²100climate scenarios data in TibetanPlateau under the latest RCP4.5and RCP8.5climate change scenarios, and drive modified LPJsimulating the future Tibetan plateau vegetation distribution and NPP pattern which impacted byclimate change, discussed how the vegetation distribution and NPP change. The main results andconclusions are as follows:（1） In this study,10kinds of PFTs （plant functional types） of LPJ model has added on thebasis of original10kinds of PFTs, and got19kinds of PFTs finally according to integration andmodification, which including changing bioclimatic limits and physiological ecologicalparameters of PFTs, and modifying biogeochemical parameters of the module. Throughcommissioning and validation, a modified LPJ model suitable to simulate in Tibetan Plateau comeout ultimately. By using kappa statistics method and comparing with the other research resultsproved that the effect of simulating vegetation distribution and NPP pattern in Tibetan Plateau bymodified LPJ model was well.（2） The modern simulation results from modified LPJ model showed that, the vegetationdistribution of the Tibetan Plateau displayed obvious level zonal characteristics, as forest-shrub-alpine meadow-alpine grassland-desert vegetation pattern from the southeast to the northwestregion in the plateau. Needle leaved and broad leaved forests were concentrated in southeasternregion and northern edge of the Tibetan Plateau. Shrub mainly distributed in the east and southeastpart of plateau. Alpine meadow was widely distributed in the vast eastern region. Alpine grasslandwas the most widely distribute vegetation type, and mainly in the West （Northwest） and northeastregion of the plateau. Desert vegetation mainly distributed in the western Ngari and northernfringes of plateau. At the same time, there was a large area of bare land located in the northwest edge of plateau. The vegetation types of the Tibetan Plateau shows a pyramid characteristics, thegrassland and meadow which are more suitable for alpine arid environment hold a dominantposition.The simulation of NPP showed that the annual average NPP was234TgC a^-1(as249.5ofgC m^-2 a^-1) between1961and1990in Tibetan Plateau. The distribution pattern of NPP alsoshowed level zonal characteristics, decreased gradually from southeast to northwest region,reduced from524of gC m^-2 a^-1to about55of gC m^-2 a^-1, and the minimum value close to0appeared in the northwest of Kunlun Mountains and Tsaidam Basin. The NPP of broadleafforest was the highest comparing with the other vegetation types, reached575.6gC m^-2 a^-1, andthe NPP of coniferous forest was239.4gC m^-2 a^-1, shrub was67.5gC m^-2 a^-1, alpinemeadow was271.8gC m^-2 a^-1, alpine grassland was154.8gC m^-2 a^-1, the lowest value was51.8gC m^-2 a^-1of the desert. According to classification of vegetation NPP, the ecosystem ofthe Tibetan Plateau was the low or extremely low productivity areas.（3） Simulation under future climate change scenarios show that the broad leaved forests inthe Tibetan Plateau mainly locate in the southeast region and its area will greatly extend. Needleleaved forests tend to increase and gradually extend to the hinterland of the plateau. Theincreasing trend of shrub is the most obvious； it will gradually become the dominant vegetationin the eastern region of plateau. The distribution area of alpine meadow reduces, mainly because itis partly replaced by shrub. Grassland expands to the northwest of the plateau, and the distributionarea has increased significantly, covering a large area in western and northern regions of theplateau. Because of westward extension of the grassland, the bare area is constantly shrinking. Thechanging trend of the plateau vegetation types under future climate change scenarios is significant,and its overall direction is conducive to the ecosystem progressive succession, the vegetationcoverage will gradually increase.（4） The Tibetan Plateau vegetation NPP under the future climate change scenarios shows aoverall upward trend. The rise from baseline period （1961to1990） to final phase （2071²100） is78.8%（under RCP4.5scenario） and133.6%（under RCP8.5scenario）. The statistic of classifiedNPP levels show that, the distribution area of200⁴00gC m^-2 a^-1and0²00gC m^-2 a^-1decrease, and its distribution range mainly locate in the west Kunlun Mountains corresponding tothe bare ground and scattered grassland. The proportion of NPP400⁶00gC m^-2 a^-1steadilyrise, the distribution move from the eastern part of the plateau to the central and western regionswhich covered by alpine grassland. The distribution area of600⁸00gC m^-2 a^-1and800¹000gC m^-2 a^-1level of NPP significantly increase, gradually occupy a large area of the easternplateau. The range of NPP gC m^-2 a^-1is gently expanding, and the correspond vegetation typesare broad leaved and needle leaved forests, locate in southeast of plateau with better heat andhumidity condition.Changes of NPP under future climate change scenarios also have obvious spatial distributioncharacteristics. Overall, the NPP of each region in the Tibetan Plateau are rising generally, the rate of rise render a law that increasing from east region to west region, and reducing gradually overtime. At the end of21century, the increase rate of NPP will reach above200gC m^-2 a^-1in mostparts of the plateau, but smaller in Ali Plateau, hinterland of northern Tibetan, southeastern edgeof the plateau and Tsaidam Basin. It’s worth noting that NPP of bare areas in the northwest regionis not changing obviously, NPP of the broad leaved and needle leaved forests in the southeast ofplateau show a negative growth trend in general.