气候和竞争对亚热带杉木人工林单木生长的交互作用

Adaptive forest management needs quantifying the effect of climate on tree growth, but competition can confound relevant results. Physiological studies show that tree growth can be affected by the interactions between climate and competition, which were not included in the present forest growth models. Based on previous studies, this study would focus on the key problem which is How to Quantify the Interactions between Climate and Competition on Individual Tree Growth and Chinese fir plantations in subtropics in China. This study will be mainly engaged in two contents. First, individual tree growth models will be constructed and climate, competition and their interactions should be included in the models. Double screening of stepwise regression method will be used to select the factors which may have significant effects on individual tree growth. And three methods (potential growth with modifiers, regression estimates, growth analyzing) will be used to construct individual tree growth (diameter, height and crown width), and regional-scale and plot-scale random effects parameters will be contained in the final models. Second, a solid estimate of the interactions between climate and competition will be obtained by bootstrap. The initial data will be regarded as population, and individual tree growth under different extreme environmental conditions will be calculated by bootstrap. Thus, the solid estimate of the interactions which would be between climate and competition can be obtained. This study will be used to model the growth of reserved trees after stand density control measures, and provide scientific evidences for forest adaptive management.

度量气候对树木生长的影响是适应性森林经营的需要，而竞争会对相关的研究结果造成干扰。树木生理方面的研究已经发现树木生长会受到气候和竞争的交互作用，而现有的模型中没有考虑这一点。由此，本研究围绕“如何度量气候和竞争对单木生长的交互作用”这一问题，以亚热带杉木人工林为对象，主要开展：（1）含气候和竞争及其交互作用的单木生长模型的构建。拟采用双重筛选逐步回归法筛选出对单木生长有显著影响的因子，再采用潜在生长量修正法、回归估计法和生长分析法构建单木生长（胸径、树高、冠幅）模型，并添加区域尺度和样地尺度的随机效应参数；（2）基于自助法的气候和竞争对单木生长的交互作用的稳健估计。以原始数据为总体，采用自助法计算各极端条件单木生长的情况，以此获取气候和竞争对单木生长的交互作用的稳健估计。研究结果可用于模拟林分密度控制措施后保留木的生长状况，从而为森林的适应性经营提供科学依据。

度量气候对树木生长的影响是适应性森林经营的需要，而竞争会对相关的研究结果造成干扰，现有的模型很少考虑到气候和竞争对树木生长的交互作用。项目以亚热带杉木人工林为对象，基于连续观测的167块固定样地数据、40块临时样地及18个林分中优势木和平均木二类树木的36株解析木数据及气象数据，构建了单木树高-胸径和冠幅-胸径模型，研建含气候和竞争及其交互作用的单木生长模型，揭示气候和竞争对单木生长的交互影响，并模拟和预测未来气候变化情景下的不同竞争压力下单木生长的变化。其中，单木生长模型采用潜在生长量法和分位数回归模型构建。由于数据的重复观测和层次性，采用混合效应模型进行参数估计，并采用自助法生成了1000个伪数据集，以此获得参数的分布情况。结果发现同一气候因子对优势木和平均木生长影响的强度存在一定差异，各气候因子对胸径生长影响的相对重要性差异为-5.52% ~ 6.60%，对树高生长影响的相对重要性差异为-3.66% ~ 6.54%，对材积生长影响的相对重要性差异为-5.17% ~ 10.10%；年最大温差是影响单木生长最主要的气候因子，而对胸径、树高、冠幅生长起主要影响的地形因子和竞争指标并不一致，其中对胸径生长起主要影响的地形因子和竞争指标为坡度和累积分布函数，对树高生长起主要影响的是海拔和大于对象木的断面积之和，对冠幅生长起主要影响的是坡度和大于对象木的断面积之和；气候和竞争的交互作用对单木生长表现出一定的影响，其中，交互作用对胸径生长表现出了负向效应，而对树高生长和冠幅生长表现出了正向效应。研究结果拓展了森林生长模型，为精确预估全球气候变化背景下的单木生长及建立适应气候变化的杉木人工林经营决策提供了参考。