Vertical distributions of leaf area and inclination angle, and their relationship in a 46-year-old Chamaecyparis obtusa stand

Abstract

The vertical distributions of the leaf area and inclination angle were investigated for a 46-year-old stand of Japanese cypress ( Chamaecyparis obtusa Endl.) in central Japan. The vertical distribution of leaf area per tree was measured by destructive sampling ( n = 9) and fitted to a modified Weibull cumulative distribution function (Weibull CDF). The two model parameters of Weibull CDF were derived from multiple regression analysis of tree height ( H) and whole-tree leaf area, which is allometrically derivable from diameter at breast height (DBH). Based on these relationships, the vertical distribution of leaf area density (LAD) through the canopy was computed from DBH and H data, and the stand leaf area index (LAI) was estimated to be 5.77 m 2 m −2. The leaf inclination angle, with a ‘leaf’ defined as a cluster of scale leaves attached to a primary branch, was measured for 1443 leaves that were reachable from a canopy-access scaffold tower. The average leaf angle (area-weighted) through the canopy was 41.6 ± 0.6°, decreasing exponentially from top (>55°) to bottom (30.3°). The quantitative analysis revealed a strong relationship between the average leaf angle in a canopy stratum and the downward cumulative LAD above the stratum. The leaf angle distribution ( Wg( α)) through the canopy was ellipsoidal, with different patterns in each of the three canopy layers (10.3–13.2 m, 13.3–16.2 m and 16.3–19.3 m in height). The middle canopy layer, which accounts for 81% of LAI, formed the dominant pattern of Wg( α). These measurements indicate that the level of light utilization and transmittance through the canopy is characterized by the quantitative relationship between leaf inclination angle and LAD.