不同径级油松径向生长对气候的响应

Abstract

Tree growth response to climate change in most dendrochronological studies are usually analyzed using dominant trees in a stand.However,trees′ climate-growth relationship changes in tree size,which may affect tree growth response to climate change.We built 31 tree-ring chronologies of Pinus tabulaeformis in Heilihe natural preservation areas to represent two groups of trees: dominate trees(N=15,mean diameter=43 cm) and suppressed trees(N=16,mean diameter=20cm).We analyzed differences in climate-growth relationships between two groups of trees and then 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 tree growth was evaluated by superposed epoch analysis(SEA) using nine drought years.For SEA analyses,five years prior to drought and five years following a drought year were considered.The mean sensitivity of suppressed trees were significantly higher than dominant trees(P0.01),meanwhile the signal-noise ratio and the variance in first eigenvector were much higher in suppressed than in dominant trees.Ring width indices of two chronologies were highly correlated(R=0.943,P0.01) while the raw ring widths were significantly different(P0.001).The ring-widths of all trees were significant positive correlated to precipitation of February,May,June and September of the previous year(P0.05).Growth of suppressed trees was positive correlated to precipitation of July(P0.05).The ring-widths of all samples were positively correlated to spring temperature and negatively correlated to summer temperature.Growth of all trees was significantly and negatively correlated to monthly mean temperature of June(P0.05).Dominant trees were more sensitive to climate during the previous year while suppressed trees were more sensitive to weather during the current year.In general,June was the most influential month.Precipitation appeared to be the most important factor for the radial growth of Chinese pine.SEA revealed significant growth reduction during drought years as compared to non-drought years(P 0.01) in both tree groups,indicating drought sensitivity of Chinese pine.Tree-rings in suppressed trees showed higher growth reductions caused by drought than those of dominant trees.Radial growth in all trees recovered to the level of pre-drought years in one year after drought and Suppressed trees recovered faster.Although suppressed trees were more sensitive to drought,they recovered quicker and showed more plastic response as compared to dominant trees.Dominant trees and suppressed trees showed a similar pattern in response to drought: a significant growth reduction and recovery to normal growth in the following year.Suppression appeared to enhance the effect of climate on tree radial growth.Some possible reasons for these effects are discussed.Our results reveal a pattern similar to the one in conifer species in Mediterranean region,where suppressed trees showed stronger growth reductions than dominant trees.Our results also demonstrate that suppressed trees are more sensitive to climate change.Further studies should help to evaluate the way in which tree suppression affects tree growth response to climate change in conifers in temperate continental climate.