Researhes on controll mechanism of leafarea index and light shading in tree crowns

本研究旨在从叶、枝种群动态的角度揭示树冠叶面积指数的形成机理。我在研究开始时检查了以下五个假设。(1)叶面积指数仅受耐荫性控制。叶冠下的光照强度刚好低于能维持枝条种群的最低光照条件。(2)由于冬芽大芽的数量取决于当年的条件，当年冠层下的光照条件通常低于新梢群体的最低光照条件。(3)万年青植物的老叶会挡住光线。(4)光被树干和树枝拦截。(5)夏季新梢发育后的落叶控制着冠层的叶量，从实际测量的光照条件和新梢生长来看，光照条件通常低于新梢群体的最低光照条件（Koike 1989）。树干和枝条对光照条件的影响不是很重要。通常它们只能拦截30%的全光。叶对光照条件有10倍的影响（假设4）。关于假设5，除了一些第一次和连续生长的物种外，大多数物种在夏季落叶是不常见的（Kikuzawa 1986）。这是一个三维空间的模型，由Koike（1989）从二维模型修改而来。模拟结果表明，叶面积指数与地上部种群生长速率（λ）和叶片存活率密切相关，利用冠层相互作用模型预测物种组成和优势度时，需要根据地上部和叶片动态参数精确估算叶面积指数。由于新梢群体动态影响叶面积指数，因此采用靴子带法来评价λ的可靠性。

This study aimed to reveal the mechanism of leaf area index of tree canopies from the stand point of leaf and shoots population dynamics. I checked following five hypotheses at the start of the study.(1) Leaf area index is controlled solely by shade tolerance. Light intensity under foliage canopy is just below the least light condition at which shoot population can be maintained.(2) Since number of large winter bud is determined by the condition of previous year, light condition under canopy in current year is usually lower than the least light condition for shoot population.(3) Old leaves of evergreen species intercept light.(4) Light intercept by trunk and branches.(5) Leaf fall after shoot development in summer controls leaf amount of canopy.From actual measurement of light condition and shoot growth, light condition is usually lower than the least light condition for shoot population (Koike 1989). Effect of trunk and branches on light condition is not very important. Usually they intercept only 30% of full light. Leaves have ten times of effects on light condition (hypothesis 4). Concerning hypothesis 5, leaf fall in summer is not usual in almost species, except for some first and continuously growing species (Kikuzawa 1986).A simulation model of foliage canopy growth was developed to evaluate the effect of hypothesis 2 and 3. This is a model of three dimensional spaces, and is modified from two dimensional model by Koike (1989). As the result of this simulation, the rate of shoot population growth (lambda) and leaf survivor rate were both effected leaf area index.For prediction of species composition and dominance by such canopy interaction model, precise estimation of leaf area index from shoot and leaf dynamically parameters are necessarily. Since shoot population dynamics effected leaf area index, a boot strap method was applied to evaluate reliability of lambda.