The Reconstruction Of Productivity In Mongolian Plateau Grassland From A.D.1 To 2000 And Its Response To Climate Change

Located in the eastern Eurasia grassland belt,theMongolian Plateau grassland is an essential part of the grassland ecosystem and the only path of the zonal circulation.Under the influences of the monsoon and the westerly circulation,the grassland productivity of the Mongolian Plateau almost completely depends on the climate changes.Furthermore,its ecosystem and corresponding changes can not only affect the economy,environment and national security of Northern China and even the whole Northeastern Asia,but also play an important role in the understanding of the global carbon balance.However,the research on grassland productivity of the Mongolian Plateau during the past 2,000 years is almost blank at present.Rebuilding grassland productivity changes in the Mongolian Plateau from A.D.1 to 2000 has vital scientific significance for understanding the prosperities and declines of the nomadic industry.Based on the premise of some assumptions,the measured meteorological data from 32 stations during the last 40 years were applied to reconstruct thesequence of grassland Above ground Net Primary Productivity(ANPP)in the Mongolian Plateau from A.D.1 to 2000 with the help of the CENTURY model.The high-precision historical climate data were also referred to in the simulation.The trends,abrupt changes and periodicities in the grassland ANPP were analyzed,together with their temporal and spatial distributions,and their correlations with the meteorological factors.The impacts of the increasing atmospheric CO2 concentrations on the ANPP in the Mongolian highland grassland were discussed.The main conclusions obtained are as follows:1)In the past four decades,the grassland productivity of the Mongolian Plateau has shown a fluctuating upward trend.The spatial distribution of grassland showed an irregular band distribution.From southwest to northeast,there are desert steppe,typical steppe and meadow steppe respectively.Precipitation played a leading role in the change of grassland productivity.Under the current climate change simulation of the CENTURY model,the temporal and spatial distribution of ANPP in the Mongolian Plateau grassland can reflect the changes of grassland productivity in this region.2)During the period from A.D.1 to 2000,the ANPP in the grassland of the Mongolian Plateau experienced a slight rising trend while fluctuation existed.The changing trends of the ANPP in the three types of grasslands were generally consistent with the fluctuation of the entire grassland.The ANPP of grassland was in a low value period during the little ice age of the Ming and Qing Dynasties and the Wei and Jin Dynasties,and the ANPP of grassland was in a high value period during the warm age of the Sui and Tang Dynasties.There was no mutation in ANPP in the grasslands of the entire area of grassland and the three grasslands from A.D.1 to 2000,but a significant oscillation cycle was obvious,especially in A.D.16 and during the A.D.300 to 400 periods.3)The spatial distribution of grassland in the Mongolian Plateau from A.D.1 to 2000 was roughly the same as that in the past 40 years.The area of desert steppe was the largest,while the area of meadow steppe was the smallest,and the typical steppe was in the middle of the two.The desert steppe had low yields and the total output was lowest among the three types.The response of the grasslands to different temperature and humidity matches were different.The most grassland production increased during the wet period and decreased during the dry season.The area and output of the grassland changed greatly during the wet-warm and dry-cold periods.At the same time,in different temperature and humidity matching.As for the grasslands range ability,the meadow steppe weighs the most,the typical steppe and desert steppe are smaller relatively.The response of grassland productivity to climate change also provides a certain theoretical basis for further understanding the causes of nomadic people's invasion to the Central Plains.4)The atmospheric CO2 promotes the growth of grasses.With the increasing of the concentration of CO2,it will increasingly accelerate the ANPP of the grasslands.The impact of CO2 on grassland productivity is under control of the temperature and precipitation.When the CO2 concentration increases to a certain value,its acceleration on the grassland ANPP will gradually reduce,and even become a negative effect.This phenomenon is mainly manifested in the typical steppe and desert steppe in the central and northwestern parts of the Mongolia plateau.These results above may make a contribution to understanding the global carbon cycle,the changes of grassland nomadic tribal livestock economy and provide atheoretical support to the rational development and utilization of grassland natural resources.