The Study Of Altitude Effects On Radial Growth And Climate Response Of Larix Gmelinii In The Great Xing'an Mountains

Forests around the world are subject to risk of high rates about reduced productivity of tree and increased tree mortality from combinations of climate warming and drought,notably in semi-arid settings.The forest region in the Great Xing'an Mountains is an important wood production base in China,and forest growth in this area is very sensitive to climate change,the Dahurian larch(Larix gmelinii)has experienced an unprecedented forest retreat northward during the last century in China.Whether the response of growth to climate has dissimilar patterns at different altitudes,and what the “altitudinal trends” of forest development will be in the future,remains unclear.In this paper,the dendroclimatology and dendroecology were used to investigate the impacts of climate change on the growth of larch forests along an altitudinal gradient.In total,1544 trees(2979 cores)from 50 forest stands,representing an altitudinal range from 400 to 1000 m a.s.l.in the Great Xing'an Mountains,northeast China,were sampled and used to develop the tree-ring growth index.Based on this,the dynamic change rules of the growth–climate response relationship along the elevation gradient,and the productivity and climate response threshold of Dahurian larch at different altitudes were evaluated.This will provide the basis for further understanding the growth dynamics,forest management method and future changes of Dahurian larch distribution in the study area.The main results as follows:1.The analysis of growth characteristics and spatial-temporal variation of Dahurian larch showed that the tree-ring width is generally lower than 5 mm in the study area,and the maximum width of a single tree is only 12.24 mm,The mean ring width varied obviously among different sample sites.There is a significant increasing trend in the radial growth of larch in the high altitude area(0.027 mm/ 10 a,P < 0.01),while the growth of the low-altitude area decreased(0.051 mm/10 a,P < 0.01).2.The value of BAI at all sites are generally lower than 16 cm2,the maximum is 15.435 cm2.BAI at high altitude is generally higher than that at low altitude.The biomass accumulation of Dahurian larch indicated by basal area(BA)showed a stable growth patterns at each site.The maximum BA is 2187 cm2,and the minimum BA is 280cm2.The BA showed an increasing trend with the increase of altitude.3.The correlation analysis between radial growth and climate of Dahurian larch showed that the effect of precipitation in non-growing season(previous year 10–1)on larch growth was mainly positive along the whole altitude gradient,the effect of precipitation in growing season(5–8)on larch growth is gradually changed from positive correlation at low altitude to negative correlation at high altitude(R2 = 0.466).In the non-growing season(previous year 11–1),the temperature was positively correlated with the growth of Dahurian larch at low altitude and negatively correlated with the growth at high altitude,the correlation between temperature and larch growth in growing season(6–8)changed from negative correlation at low altitude to positive correlation at high altitude.The effects of vapor pressure deficit(VPD)and standardized precipitation evapotranspiration index(SPEI)on the Dahurian larch growth during the main growing-period are respectively represented by drought restriction in low altitude area and low temperature limit in high altitude area.4.The BAI at high altitude(above 900 m a.s.l.)are generally higher than those at low altitude(below 600 m a.s.l.),and at high altitude have a long-term violent fluctuation trend.The productivity evaluation models of Dahurian larch at high and low altitude show that the warm and wet climate conditions are favorable to the growth at high altitude,while the cold and wet climate conditions are beneficial to the growth at low altitude.During the last 100 years,the sensitivity of larch radial growth increased at both high altitude(above 900 m a.s.l.)and low altitude(below 600 m a.s.l.),but increased more significantly in low altitude areas.After the mid-19 th century,the mean sensitivity(MS)of Dahurian larch at low altitude site was higher than that at high altitude area.The mean sensitivity of the raw tree-ring series of all sampling sites decreased significantly with the increase of altitude.5.Based on the growth-climate response simulations,the altitude threshold of correlation between growth and precipitation is ca.750 m a.s.l.,and the altitude threshold of correlation between growth and temperature is ca.600 m a.s.l.The mean annual temperature threshold,which is simulated by the relationship between the larch growth and the precipitation/ temperature,is ca –5? and 4?,respectively.This is shown that the growth of larch in the study area is limited by the low temperature in the area with mean annual temperature lower than –5?~ –4?,and the area above the threshold is limited by the drought.It is suggested that the growth and distribution of Dahurian larch will expand to the high altitude area in the context of further global warming and degradation at low altitude.