Abstract
The supplementary experiments for the author's last report in series**, to grasp the advanced data for clarifing the problems they were summarized in the last paper, were continued. This report is contructed with the discussions, for the response of the specific leaf area (SLA) to the decresence of the relative light intensity (RLI) in the foliage, from the data of stand analysis in the young highly congested birch (Betura platyphylla SUKATCHEV var. Japonica (MIQ.)) stand and the shaded ones. Experiments were performed from the spring to the autumn in 1972 in the training field of the University at Soshigaya in Tokyo. The data were sampled at intervals of a month, and applied into the regression formula:
logSLA(cm2/g)=blog RLI(%)+loga
Then two regression coefficients were analized, with respect to the factors they are coincident in the last report, and to the variation of the repitition in the experiments between '71 and '72. However, the difference in the coefficients of RLI-SLA regression concerning with the repitition between '71 and '72 can not be recognized entirely during the whole of the experiments. Consequently, the greater part of the sammarization in the last report was confirmed satisfactorily, and some additions and corrections to the expressions made in the last report, are made in this report as follows:
1) Seasonal trend in the inclination coefficient of the RLI-SLA regression, not only in the regressions of the stands exposed to 100% light, but of the shaded ones, can be shown as a curve which is concave up in the seasonal progress. As these trends are almostly equal to each other, with upward parallel variation at a certain seasonal time.
2) The many conditions of the stands were varied between the experiments of '72 and '71. Nevertheless and astonishingly, all of the results for many problems from the experiments in '72 and '71, take the same value and same tendency. It is confirmed sufficiently that the response of the SLA to the decresence of RLI occurs promptly, has a highly stability, and shows no fluctuation by the effects of the factors excepting the light condition.
3) In the case of the shaded stands, the beginning point which is described in RLI of the SLA value's dropping, seems to be shifted to the more lower light range, the severe the shading.
4) Dropping values of SLA under higher light exposed range and the convergence under lower range in the RLI-SLA regression curve, are recognized to appear simultaneously in the most of the cases. And the RLI at the stratum from where the dropping of SLA occurs, is equal to the RLI of a specific stratum which means the changing point in the vertical and dispersive structure of the leaf amount, for all cases in the stands. It can be said that only for the strata from the bottom of leaf layer to the specific stratum, the regressive relations for RLI-SLA seems to be equal to each other, in spite of variance being in shading condition among the stands.
5) From these facts, it might be to noted that, appling the angular line to express the RLI-SLA relations is justifiable.
