Study On The Inhibitory Effect Of Temperature On Radial Growth Of Larix Gmelinii In Da Hinggan Ling

The Da Hinggan Ling is amongst the areas in China susceptible to climate warming.The objective of this study is to determine the responses of temperature variations to radial growth in Larix gmelinii growing in various parts of the Da Hinggan Ling in the process of climate warming,by using dendrochronological techniques.We collected tree-ring samples in 15 regions from the southern,the middle and the northern parts of the main Da Hinggan Ling,developed site-specific ring-width chronologies,and synthesized tree-ring indices of the southern,the middle and the northern parts of the study area according to the geographical location of sampling sites,the first principal component loading factors for each chronology and the results of correlation analysis between chronologies.The relationships between radial growth in L.gmelinii and temperature variations were determined with correlation analysis to explore the root causes of inhibit of temperature variations to the radial growth in L.gmelinii and predict the changes of distribution of L.gmelinii forest ecosystem in a warming climate comparing with sliding response analysis and multiple linear regression model.Main findings were listed as follows:1.There are significant warming periods,accompanying with two obvious set aparts in 1920s to 1930s and 1970s to 1980s of regional temperature variation in study area.The climatic condition in the study area is sub-humid since 1960s,demonstrated a semi-arid trend since 1984,and the warm desiccation's tendency presented a trend of the middle part>the southern part>the northern part.The permafrost type in study area is discontinues permafrost.The most serious of permafrost degradation occurred in the 1925-1955 and 1969-1999,and there is no distribution of permafrost since 1988 in the southern part of the Da Hinggan Ling.The downtrend of drought index and freezing index in study presented a similar pace on the time with rapid increasement of regional temperature variation,indicated the significant changes of environmental conditions in study area under climate warming.2.The grow amount of trees directed by basal area increment(BAI)presented a trend of the middle part>the southern part>the northern part in the same time.The BAI exerted a downward trend in the southern and middle parts of study area along with the temperature went up,including a sunificant decline in the middle part of Da Hinggan Range since the lastest temperature set apart.This presented a similar pace on the time with rapid increasement of regional temperature variation as well as the changes of environmental conditions,predicting that increased temperature inhibit the radial growth of L.gmelinii and the inhibition variated in different regions.There were notable discrepancies in the influences of temperature variations on radial growth of L.gmelinii in the study area(the middle part>the northern part>the southern part).In the southern part,the mean monthly temperature between the previous Nov,and Apr,of the current year had a significant relationship with tree-ring indices(p<0.05).In the middle part,the mean seasonal temperature of previous growth season and last winter had a significant relationship with tree-ring indices(p<0.05),and so did the mean seanal temperature of current autumn(p<0.05).The mean monthly temperature during April and May of the current year(pre-growth season)had a highly significant relationship with tree-ring indices in the northern part(p<0.01).This study suggests that the warmer and drier regional climate condition caused by elevated temperature has resulted in that soil moisture becomes the main factor limiting the radial growth,and the relationship between tree growth and temperature variations signified with aggravated soil drought under climate warming.The productivity in L.gmelinii as reflected by basal area increment experienced a shift response from cold stress to water stress.In addition,the radial growth in L.gmelinii in the Da Hinggan Ling will likely to show a declining trend in the southern and the middle parts,and an increasing trend in the northern part,in response to rapid warming in the imminent decades.However,the role of natural reserve to radial growth of L.gmelinii in northern Da Hinggan Ling is immutable.The decline of response coefficients between temperature variation and tree-ring index in L.gmelinii in northern part of Da Hinggan Ling announced that the suitable area of L.gmelinii had moved northward.The balance of the L.gmelinii forest ecosystem may be damaged and superseded by climate warming in the future.