Growth Response To Climate In Chinese Pine As A Function Of Tree Diameter

In dendrochronological studies, the effect of non-climatic signals is always removed from the series of tree-ring widths. Therefore it is generally assumed that the climate-growth relationship is class diameter independent. However intensive physiology studies have shown that tree’s physiological process is related to diameter, while tree’s growth is affected by climatic factors via physiological process. In this paper we built chronologies of two diameter classes of Pinus tabulaeformis from4sample sites:Heilihe(HL), Keqi(KQ), Songshan(SS) and Ningxia(NX). We analyzed differences of sensitivity between two groups of trees, built climate-growth relationships and discussed whether drought differentially affected the ring-widths in these groups. Climate-growth relationships were analyzed using the correlation and response functions and the effect of drought on trees’growth was evaluated by superposed epoch analysis (SEA) using nine drought years. The results showed that:1) The relationship between mean sensitivity and DBH were different in different sites. The relationship was a significantly negative correlation in sites HL and KQ while there were no significant correlation in sites NX and SS. Chronologies of different diameter classes in the same site were significantly correlated(P<0.01).2) Growth of P. tabulaeformis in all sites were positively correlated to precipitation and negatively correlated to temperature in summer. Climate in spring and summer were most important factors that affecting growth of P. tabulaeformis. A warm-wet spring and cool-wet summer enhanced radial growth. There were hysteresis effects of precipitation to radial growth. The ring-widths were significantly positive correlated to September in last year(HL and SS), October in last year(KQ).3) SEA revealed significant growth reduction during drought years as compared to non-drought years (P<0.01) in both tree groups(HL and KQ) and recovered to the level of pre-drought years in one year after drought, indicating drought sensitivity of Chinese pine. In HL, the reductions of small DBH trees were significant higher than the large DBH trees(P<0.01). In KQ, there were no significant differences between the groups. It can be concluded from the results that:1) in the sites HL and KQ, the relationship between sensitivity and DBH was significantly correlated and the sensitivity of small DBH trees were higher. While in site NX and SS there were no significant correlation.2) P. tabulaeformis is drought sensitive species, showed significant reduction in drought years and recovered to normal in one year. The response of radial growth to drought was significant different in site HL while there were no differences in site KQ. The mean sensitivity and responses to drought of different classes were affected by the local climate. The growth-climate relationship were not stable among diameter class, therefore DBH should be considered in sampling procedure to produce unbiased results.