张广才岭北部三大硬阔树木生长-气候关系的时空变异

树木年轮在时空尺度上的比较可以更好地反映环境变化对树木生长的影响,在认识气候变化对森林生态系统的影响上具有重要意义。采用树木年代学方法分析了张广才岭北部地区阔叶红松林中主要阔叶树种-水曲柳(Fraxinus mandshurica)、黄菠萝(Phellodendron amurense)和胡桃楸(Juglans mandshurica)径向生长与气候关系的时空变异。结果表明,在同一地点树种间气候响应差异明显,胡桃楸受降水和最低温度共同作用,而黄菠萝和水曲柳则主要受最低温度限制,这表明树木生长与气候因子的关系具有一定的物种特异性。随着温度和降水格局的改变,三大硬阔年轮与气候关系在空间水平上存在差异,方正和西大圈样点的胡桃楸与6—8月最低温度呈显著正相关(P0.05),而凤凰山样点与5、6月最低温度和降水呈正相关(P0.05);黄菠萝和水曲柳径向生长随着降水空间格局的变化,其生长季末期相关性程度逐渐减弱。1980年后张广才岭北部出现气温显著升高,在升温前三大硬阔的生长趋势相对一致,而在升温后黄菠萝和水曲柳树轮宽度随温度升高呈上升趋势,但胡桃楸却出现随温度升高而生长下降的"分异现象"。如果未来增温趋势持续发生或者加重,可以推断在张广才岭北部胡桃楸可能受干旱胁迫加剧,其可能出现生长衰退,但增温可能更有利于黄菠萝和水曲柳的生长。

Spatio-temporal variations in climate-growth relationships of three hardwood tree species across the north Zhangguangcai Mountains, northeast China

Forests play a critical role in the global ecological balance. One of the major uncertainties in global climate change predictions is how the spatio-temporal dynamics of forests will be affected by global warming. Tree rings at different spatial and temporal scales can reflect the impacts of environmental change on tree growth, and can be critical for understanding the influence of climate change on forest ecosystems. Here, we investigated the spatio-temporal patterns of variation in climate-growth relationships of three common broadleaved tree species (Fraxinus mandshurica, Phellodendron amurense, and Juglans mandshurica) in a broadleaved Korean pine mixed forest across the north Zhangguangcai Mountains, northeast China. Tree-ring chronologies from three sample sites were established, transformed into principal component analysis (PCA), and analyzed through correlation analysis. With these analyses, climate factors limiting the radial growth were identified, as well as the detailed spatial radial growth-climate associations. The responses of the tree species at similar sites to climate factors differed significantly. Radial growth of J. mandshurica was limited by monthly total precipitation and minimum temperature, whereas P. amurense and F. mandshurica were mainly affected by monthly mean minimum temperature. This suggests that climate-growth relationships are affected by species-specific characteristics. With changes in temperature and precipitation patterns, the three hardwoods differed in their spatial growth response to climate factors. The radial growth of J. mandshurica in Fangzheng and Xidaquan was positively correlated with minimum June to August temperatures (P<0.05). In contrast, it was positively correlated in Fenghuangshan with minimum temperature and precipitation in May and June (P<0.05). The radial growth of P. amurense and F. mandshurica decreased from west to east with precipitation changes, since the correlation coefficients between tree-ring index and precipitation decreased from west to east. Temperatures in the north Zhangguangcai Mountains have increased since 1980, and the radial growth of the three hardwoods was consistent before 1980. Because climate factors affect growth differently, these boreal tree species showed inconsistent spatio-temporal responses to the recent warming, with J. mandshurica being probably the most sensitive species. Radial growth of P. amurense and F. mandshurica increased with rapid warming since 1980, whereas tree growth of J. mandshurica decreased after 1980. Therefore, J. mandshurica may be subjected to drought stress and a subsequent decline in radial growth in the north Zhangguangcai Mountains if global warming continues or exacerbates. In contrast, P. amurense and F. mandshurica may benefit from increased temperatures through enhanced radial growth. For future research, the spatio-temporal variation of growth-climate relationship of the three hardwoods could be explored further by investigating the tree ring anatomical and physiological responses.