RESPONSE OF PINUS TABULAEFORMIS TREE-RING GROWTH TO THREE MOISTURE INDICES AND JANUARY TO JULY WALTER INDEX RECONSTRUCTION IN HELAN MOUNTAI

There is an evident correlation between tree-ring RES chronology and three different moisture indices (PDSI, Walter index, drought index).The results showed Pinus tabulaeformis tree-ring growth in Helan Mountain responded to each moisture index of growth-season period pretty well,especially is that correlation coefficient between RES and the mean Walter index (WI) from January to July is r=0.76 (n=30,p<0.001),indicating water deficiency in growth season is the predominant limiting factor for Pinus tabulaeformis growth in Helan Mountain,thus it's less reasonable to consider precipitation or temperature independently as the limiting factor for tree growth.Walter index with temperature and precipitation taken into account can better reflect water content for the tree growth than the other two indices in Helan Mountain.Based on regression model,we reconstructed the mean WI from January to July in Helan Mountain for the last 200 years,and the reconstruction captures 58% (F=38.73,p<0.001) of the actual PDSI variance during their common period from 1960 to 1990.