人工长白落叶松幼龄林树冠比叶重

比叶重(LMA)是构建生态系统过程模型的重要参数之一,准确预测树冠比叶重的动态变化对提高模型精度有重要意义。本研究以黑龙江省尚志市帽儿山林场人工长白山落叶松为对象,分别在生长季针叶不同发育时期对树冠内不同垂直位置的针叶比叶重进行测量,分析针叶比叶重在树冠垂直方向及针叶不同发育时期的变化规律,探讨导致其时间和空间差异的主要因子,建立长白落叶松幼龄林比叶重动态预估模型。结果表明: 比叶重在树冠垂直方向表现为随着相对着枝深度(RDINC)的增加而减小,完全展叶后比叶重在垂直方向的变化幅度明显高于展叶初期。比叶重在不同发育时期表现为随发育进程先增大后趋于稳定,该趋势随着树冠深度的增加而逐渐减弱。分别以RDINC和年度积日(DOY)为单一变量预测比叶重时,模型的调整后决定系数(R_a²)低于0.6,当同时以RDINC和DOY为自变量构建比叶重预估模型时,R_a²提高0.19,且模型检验效果良好(ME=0.54 g·m^-2, MAE=5.74 g·m^-2)。研究表明长白落叶松比叶重在树冠不同轮层和不同针叶发育期间均存在显著差异,以RDINC和DOY为自变量构建的比叶重预测模型可以很好描述长白落叶松比叶重的空间及生长季针叶发育期变化,为阐明树冠发育机理提供理论依据,为提高生态过程模型精度奠定基础。

Prediction of crown leaf mass per area for young Larix olgensis plantation

Leaf mass per area (LMA) is an important parameter in the construction of the ecosystem process models. Accurate prediction of the dynamic validation of canopy LMA is of significance to improve the accuracy of ecosystem process models. We conducted vertical whorl-by-whorl sampling and analyzed LMA in different seasons for Larix olgensis plantation in Maoershan in Shangzhi, Heilongjiang Province, China. We analyzed the vertical and developmental variations of LMA and their main effective factors, established the dynamic prediction model of LMA for young L. olgensis plantation. The results showed that the LMA decreased with the increases of relative depth into crown (RDINC) in the vertical direction of the crown. The range of LMA in the vertical direction after leaf expanded was significantly larger than that during leaf expanding. During the different development periods of leaves, LMAs increased first and then remained stable, and this trend gra-dually weakened with the increases of crown depth. The R_a² values were lower than 0.6 when RDINC or DOY were used as the single variable to model LMA, but were increased by 0.19 when both of them being used, and the model performed well in validation (ME=0.54 g·m^-2, MAE=5.74 g·m^-2). LMA varied across different crown whorls and different leaf development periods. The LMA model constructed with RDINC and DOY could well describe the vertical and temporal variations of LMA. The simulation of crown LMA provided a basis for clarifying crown development and a foundation for the establishment of ecological process model.