Holocene Vegetation Changes And Response Regimes In Mountain Area Of Central Inner Mongolia: Based On Pollen Record Of XHZ Lake Core

The study of the Holocene vegetation change and response regimes in the marginal monsoon region of northern China is of great significance because it can provide some references for predicting the vegetation change in response to climate warming in the future.In this paper,based on the well-dated and high-resolution fossil pollen record of Xihaizi lake core(XHZ core)in Chahar Right Back Banner,Inner Mongolia,we reconstructed the vegetation history during the past 10,980 years in the mountain area of the east Daqingshan mountain.Moreover,multi-statistical analysis including redundancy analysis(RDA),sensitivity analysis(Pearson correlation)and Squared-chord distance(SCD)analysis were performed on XHZ fossil pollen data and potential influencing variables including Asian winter monsoon(WM),Asian summer monsoon(SM),mean annual temperature(MAT),mean summer temperature(MST),and human impact index(HII),to explore possible forcing and response regimes.Besides,we synthesized 16 Holocene Pinus,Betula and Quercus pollen percentage sequences in marginal monsoon area and its adjacent area of northern China and reconstructed the Holocene spatial-temporal pattern of each species on the basis of the threshold percentages to reflect the stand of their parent plants.Furthermore,we discussed the evolution and response regimes of mountain forests in the northern monsoon margin region.The primary results are as follows:The XHZ pollen-reconstructed Holocene vegetation changes since 10.98 cal.kyr BP can be divided into six stages.Steppe extensively prevailed in the study area between 10.98 and 10.18 cal.kyr BP;sparse birch and elm forest-steppe prevailed during 10.18 to 7.76 cal.kyr BP with sparse birch forest in shady slopes of high elevation,temperate deciduous forests at middle elevations,and steppe extensively in sunny slope and lower elevation area;birch,elm and oak forest grassland during 7.76 to 6.10 cal.kyr BP when temperate deciduous forest expanded in the middle and lower elevation area and steppe reduced but absolutely dominated the study;pine-birch woodland steppe dominated during 6.10 to 1.94 cal.kyr BP with temperate deciduous forest greatly degraded at middle and lower elevation areas;mountain pine woodland steppe developed during 1940 to 130 cal.yr BP as all other forest retreated at all elevation;steppe absolutely dominated the study area while all types of forest disappeared during the past 130 years.RDA analysis,sensitivity analysis and SCD analysis of XHZ pollen combination suggest that the vegetation change main responded to the temperature during 11.0 to6.0 cal.kyr BP,and this response regimes changed to the SM since 6.0 – 0 cal.kyr BP.The vegetation change rate was controlled by summer monsoon precipitation and temperature in a millennium scale,suggesting a stable vegetation change in warm and humid conditions.The vegetation stability was influenced by the changing rate of the summer monsoon and the annual mean temperature in the century scale.Based on the reviews and synthesis of the 16 fossil pollen sequences in the marginal monsoon area of northern China following,we explored the Holocene evolution and dynamics of three main forest species.We found that the forest in the south changed its forest constituents in response to monsoon change,whereas the forest in the north changed its cover in response to monsoon change.We argued that local refugia in wet valley of mountains for quick expansion of forest in response to monsoon strengthening.