山西省长治市过去150年森林的生长抑制和释放历史

森林生长与气候变化有着紧密的关系,在全球变暖情形下了解树木的干扰历史对准确预测森林生长的变化具有促进作用。本文选择山西黄土高原东南部长治地区保存较好的一个油松(Pinus tabuliformis)和两个白皮松(Pinus bungeana)森林为研究对象,利用树木年轮学方法分析了其干扰历史。结果表明:黎城县、平顺县和屯留县研究地点中年龄最老的树木分别有227、185、102a;通过计算树木径向生长的变化幅度,发现该地区在过去150年中发生了3次大的生长抑制事件(分别发生在1873—1877、1925—1930和1994—1997年期间)和5次大的生长释放事件(分别发生在1867—1871、1878—1884、1930—1935、1980—1985和1999—2004年期间)。树木径向生长与气象观测资料的相关分析显示,该地区森林生长在年际尺度上主要与6月份温度呈负相关而与4—5月份水分条件呈正相关,揭示了由降水减少或高温下水分蒸散所带来的极端干旱事件是导致森林抑制现象的主要原因。这些森林历史研究结果对区域林业管理具有实践意义,营林建设更宜选择在森林生长释放时期;经历多次干扰而存留下来的老龄树具有较强的抗干扰能力和丰富的历史信息,加强对老龄树的鉴定与针对性保护可有效维护区域森林生态服务功能。

History of growth suppression and release events in forests in Changzhi Prefecture, Shanxi Province, China

Forest growth is closely associated with climate change, and understanding the history of growth disturbances can help predict potential changes in forest growth caused by global warming. In this study, we utilized dendrochronological methods to study growth release and suppression events of trees in order to reconstruct the disturbance history of forests. A total of 27 samples were collected from one Pinus tabuliformis forest and two Pinus bungeana forests in Changzhi Prefecture (southeast of Loess Plateau). After measuring and cross-dating the tree ring width, we found that the oldest trees in the Licheng, Pingshun, and Tunliu sampling sites were 227, 185, and 102 years old, respectively. Percentage of growth change (GC%) was calculated to identify the disturbance events. Growth release was defined as an average GC% (five years) of more than 0.25, while growth suppression was defined as an average GC% (five years) of less than-0.25. In this study, the results indicated that in the past 150 years, growth suppression occurred three times (1873-1877, 1925-1930, and 1994-1997), while growth release occurred five times (1867-1871, 1878-1884, 1930-1935, 1980-1985, and 1999-2004). Although the three forests had similarities in their disturbance histories, there were also differences in their spatial and temporal scales. These differences may be caused by the genetic characteristics of the different species and local environmental variations. To further understand the causes of the disturbances, a correlation analysis was performed for the first order difference of the three tree ring width chronologies and the meteorological records. The correlation coefficients showed that forest growth was negatively correlated with June temperature and positively correlated with April-May precipitation. This suggested that the historical growth suppression events might be related to extreme drought events, caused by precipitation reduction or excessive water evapotranspiration, whereas the growth release events might be related to an abundant supply of water. To validate these results, we compared our study with historical records and local paleoclimate studies. The drought events recorded in the historical materials, and reconstructed using other paleoclimate studies reasonably fit our results, which indicates that our study successfully rebuilt the historical growth history and that dendrochronological methods could be used in forest disturbance research in the east edge of the Loess Plateau. This study provided useful information for forestry management. For example, forest plantations should be carried out in moist conditions during the growing season. The old growth trees that survived multiple disturbance events have strong resilience and contain valuable information about historical environmental changes; identifying and protecting old growth trees is important for maintaining efficient and healthy forest ecosystem services.