中国北部不同地点樟子松人工林径向生长对气候响应的差异

Differences in tree-ring growth response of Pinus sylvestris var. mongolica to climatic variation at different locations in northern China

通过树木年代学方法,测定了毛乌素和塞罕坝相同密度樟子松(Pinus sylvestris var.mongolica)全木(Ringwood,RW)、早材(Earlywood,EW)和晚材(Latewood,LW)宽度,计算胸高断面积增量(Basal area increment,BAI),并建立了樟子松年轮宽度年表,分析其对气候响应的差异。结果显示,毛乌素(Mu Us)樟子松轮宽随树龄呈"升-降"的曲线变化,塞罕坝(Saihanba)呈线性下降,两地樟子松BAI变化相似,呈"升-降"的曲线变化,EW占RW的65%—70%,表明EW对RW贡献较大。生长期间,毛乌素樟子松早晚材比例保持平稳,塞罕坝EW/RW值下降,LW/RW值上升,两地干旱事件均使LW/RW值下降,EW/RW值上升。差值年表(Residual chronology,RES)相关性分析显示,毛乌素樟子松径向生长主要与4、7月平均降雨,7月标准化降水蒸散发指数(Standardized precipitation evapotranspiration index,SPEI),3、8月平均温度及上年12月和当年3月最低温度呈正相关关系,与上年11月和当年6月最高温度呈负相关关系。塞罕坝樟子松径向生长主要与7、8月平均降雨、SPEI和最低温度呈正相关关系,与当年3、5月最高温度呈负相关关系。结构方程模型表明,毛乌素年平均温度和年SPEI对樟子松RW产生极显著负效应,年平均降雨对RW产生显著正效应,年平均降雨对EW产生极显著正效应,年最低温度和年平均温度分别对LW产生极显著正/负效应。塞罕坝樟子松径向生长对其年气象因子响应与毛乌素相似,但有部分差别,塞罕坝年平均降雨对LW产生极显著负效应,但对EW未达到显著性水平,且年SPEI对塞罕坝樟子松RW和EW产生的干旱胁迫效应明显小于毛乌素。

A tree-ring width chronology of Mongolian pine(Pinus sylvestris var. mongolica) in northern China was established to analyze the tree growth response to climatic variation. The widths of Ringwood(RW), Earlywood(EW), and Latewood(LW) of Mongolian pine trees with the same wood density growing at Mu Us Desert and Saihanba National Forest Park were measured from tree-ring chronologies. Differences in the response of Mongolian pine trees to climatic variation were analyzed by measuring basal area increment. The results showed that the tree-ring width of Mongolian pine at Mu Us Desert presented a trend to initially increase and thereafter decrease with the increase in tree age, whereas at Saihanba tree-ring width showed a linear decreasing trend with tree age increase. The variation in basal area increment of Mongolian pine was similar to that of tree-ring width at the two study sites. The proportion of EW(as a percentage of RW) ranged from 65% to 70% at the two study areas, which indicated that the growth of EW made a greater contribution to RW than that conferred by LW growth. During the growth period, the relative percentages of EW and LW in the RW of Mongolian pine at Mu Us Desert showed only slight variation, whereas at Saihanba the percentage of EW decreased and the percentage of LW increased in the tree RW. The percentage of LW in the RW decreased during three drought events at Mu Us Desert. Correlation analysis showed that the radial growth of Mongolian pine at Mu Us Desert was positively correlated with the rainfall in April and July, the standardized precision evaporation index(SPEI) in July, the average temperature in December of the previous year and in March of the current year, and the minimum temperature in March and August, and was negatively correlated with the maximum temperature in November and June of the previous year. The radial growth of Mongolian pine at Saihanba was positively correlated with the rainfall in July and August, the SPEI, and the minimum temperature, and was negatively correlated with the maximum temperature in March and May of the current year. Structural equation modeling analysis showed that the annual average temperature and annual SPEI at Mu Us Desert had significantly negative effects on RW growth of Mongolian pine, the annual average rainfall had significantly positive effects on both EW and RW growth, and the annual minimum temperature and the annual average temperature had significantly positive and negative effects on LW growth, respectively. The responses of radial growth of Mongolian pine to the annually meteorological variables at Saihanba were generally similar to those observed at Mu Us Desert, but some differences were noted. The annual average rainfall had a strongly significant negative effect on LW of Saihanba, whereas the impact on EW did not attain significance. The drought stress effect of annual SPEI on RW and EW of Mongolian pine at Saihanba was significantly smaller than the impacts on RW and EW at Mu Us Desert.