Aboveground biomass and vertical distribution of crown for Taiwan red cypress 20 years after thinning

Abstract

The aim of this study was to analyze the influence of thinning on the different growth stages of the Taiwan red cypress (Chamaecyparis formosensis Matsum) on the aboveground biomass allocation patterns and vertical distribution of foliage and branch biomass at the tree level. Although numerous studies in various fields have focused on the influence of thinning effects for Taiwan red cypress, few have assessed the above- ground biomass allocation of different growth stages, or conducted a long-term thinning observation. In this study, we examined 3 even-aged plantations in central Taiwan. In 1982, 3 stands, at ages 7, 15, 21 years, si- multaneously began thinning trials. A thinning study was conducted once 20 years ago, and we assessed the long-term effects. The effects of thinning in each of the stands were analyzed and compared at the tree level 20 years later. Each component of the aboveground biomass (foliage, branches, and boles) increased with the thinning intensity, regardless of the age category of the trees; however, the crown mass/ aboveground tree mass appeared the same for each tree age category, regardless of the thinning intensity. We inferred that this phenomenon might result from the same proportional increase of crown mass and aboveground tree mass as the thinning intensity was increased. An allometric function was used to quantify the vertical distribution of the foliage and branch biomass; the results showed an increase in the accumulation of the branch biomass at lower heights following thinning, and the same trend was apparent in all 3 plantations.