Biomass allocation to leaves, stems and reproductive organs in Japanese cedar plantations with different stand densities

Abstract

Aboveground net primary production and its allocation to different organs were evaluated along the gradient of stand density in three thinned and three control plots at a Japanese cedar plantation in northern Ibaraki Prefecture. The aboveground net primary production rate after thinning differed 1.9-fold among six study plots. The mean biomass allocations to stems, leaves, cones, and male flowers for the six plots were 64.7%, 27.3%, 3.0% and 3.0%, respectively. The plot with the lowest relative yield index had lower allocation to stems (54%). Two other thinned plots had higher allocation to stems (71-72%). Allocation to stems in the unthinned plots had intermediate values (61-67%). By excluding one control plot with high male flower production, allocation to male flowers was higher where the relative yield index was lower. These results suggest that strong thinning promotes allocation to male flowers but not to stems, and that stand density should be maintained at a certain level as the relative yield index is 0.75 to maintain allocation to stems and inhibit increase in male flower production.