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

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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.