哀牢山中山湿性常绿阔叶林木径向生长季节动态及其对气候因子的响应

研究采用树木生长环在哀牢山中山湿性常绿阔叶林持续9年(2009—2017年)监测了2个常绿树种(厚皮香,Ternstroemia gymnanthera;南亚枇杷,Eriobotrya bengalensis)和2个落叶树种(西桦,Betula alnoides;珍珠花,Lyonia ovalifolia)的树干月生长量,采用逻辑斯蒂生长模型(Logistic model)模拟树木径向生长量和物候参数,并分析了年、季尺度上径向生长与主要气候因子的关系。结果表明:1)4个树种年平均生长量为6.3 mm,落叶树种年平均生长量(10.6 mm/a)显著高于常绿树种(3.0 mm/a);2)雨季(5—10月)是哀牢山中山湿性常绿阔叶林树木生长的主要时期,4个树种雨季平均生长量为5.9 mm,占全年总生长量的93%,其中落叶树种雨季生长量占全年的96%,而常绿树种雨季生长量占全年的86%;3)常绿树种生长季长度为169天,长于落叶树种(137天),而落叶树种最大生长速率(0.14 mm/d)显著高于常绿树种(0.03 mm/d),最大径向生长速率能很好地预测树种年生长量;4)低温、雾日和光合有效辐射是影响哀牢山亚热带常绿阔叶林4个研究树种径向生长的重要环境因子,其中温度对常绿树种径向生长具有显著影响,而雨日、雾日与空气湿度等水分因子对落叶树种径向生长更为重要。常绿树种年生长量对旱季气候因子的响应相比落叶树种更为敏感,树木旱季生长量除了受低温限制外,也受到水分供给的影响。气候变化可能改变不同物候类型树种在哀牢山中山湿性常绿阔叶林中的生长状态与分布格局。

Intra-annual radial growth of evergreen and deciduous tree species and their response to climatic factors in a montane moist evergreen broad-leaved forest in the Ailao Mountains, Southwest China

This study monitored intra-annual stem diameter growth of two evergreen (Ternstroemia gymnanthera, Eriobotrya bengalensis) and two deciduous tree species (Betula alnoides, Lyonia ovalifolia) for a 9-year period (2009-2017) in a montane moist evergreen broad-leaved forest in the Ailao Mountains, southwest China. The metal band-dendrometer technique was used to measure stem diameter. We modeled growth phenology (i.e., start day, stop day, growth duration, and annual growth) with a logistic model, and analyzed the associations between annual and seasonal growth and climate factors over the study period. The deciduous trees had an average annual growth rate of 10.6 mm over the study period, and the evergreen trees had an average annual growth rate of 3.0 mm. The average annual growth rate of all four species was 6.3 mm. On average, trees grew 5.9 mm during the rainy season, which accounted for nearly 93% of annual growth. Deciduous trees showed higher growth rates than evergreen trees during the rainy season. Compared with deciduous trees, evergreen trees started growth earlier and stopped growth later. Annual total growth of the four studied species were highly related to their maximum growth rates during the rainy season, but less correlated with the length of the growing season. Temperature was the main limiting factor for stem growth of evergreen tree species, while precipitation days, fog days, and relative humidity were more important for stem growth of deciduous tree species. The different growth-climate relationships between evergreen and deciduous tree species implies that ongoing climate change may alter tree growth rates and species composition of subtropical evergreen broad-leaved forests.