Effect of light condition in the stand upon the height of the lowest living branches of young Pinus thunbergii Parl. at Horikawa Study Site, Akita, was demonstrated in this study. The study site was set up in 2010, and composed of five different density-controlled plots (Un-thinned, 10,000, 5,000, 2,500, and 1,000 trees/ha Plots). On 31 Oct. – 1 Nov. 2019, we measured the photosynthetically active photon flux density (PPFD) both in each plot and outside the plot to evaluate the relative PPFD (rPPFD) in the stand. We also measured PPFD above the leaves of the lowest living branches in Un-thinned Plot and 1,000 trees/ha Plot. Besides, we selected the lowest dead branches with fresh yellow discolored leaves on the same focal trees in 1,000 trees/ha Plot, and measured PPFD above the yellow leaves. Though rPPFD on the lowest living branch of Un-thinned Plot was lower than that of 1,000 trees/ha Plot, significant negative correlation was not found between mean rPPFD and the mean height of the lowest living branches among five plots. The inconsistency might be caused by Un-thinned Plot due to the intensive self-thinning condition. If the plot wasexcluded from the analysis, we found significant negative correlation.

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