Morphological characteristics of tree crowns of Cunninghamia lanceolata var. Luotian

Abstract

The structural characteristics of the tree crowns of Cunninghamia lanceolata var. Luotian (herein, Luotian), a natural variety of C. lanceolata (Chinese-fir, herein Lanceolata) in China, were analyzed using trunk and branch measurements and biomass determinations. Samples from two typical cultivated varietal populations were collected, including twenty-six 15–23-year-old trees of Luotian from a plantation, and nine 16–23-year-old trees of Lanceolata. Our results show that Luotian and Lanceolata samples differed significantly in crown structure, morphological indices, and biomass: (1) the oldest live branches on Luotian trees were 5–6 years old and 8–11 years old on Lanceolata. The ages of the live branches were not affected by the ages of the Luotian trees, while live branch ages increased with ages of Lanceolata trees; (2) the maximum branching order of Luotian was level two. Compared to Lanceolata, the average number of first-order lateral branches (i.e., branches emerging from the trunk) and the number of first-order lateral branch whorls per sample tree were 12.9% and 32.2% lower, respectively, in Luotian. However, the average number of branches within a single whorl was 21.8% greater in Luotian; the average number of branch whorls at crown height was 51.1% greater. Thus, the Luotian variety has thicker branches; (3) the average lateral branch angles in Luotian and Lanceolata sample trees were 105.2° and 61.4°, respectively. The branch angles in 53.0% of lateral branches on Luotian ranged from 105° to 135°, but 30° to 90° in 96% of the lateral branches on Lanceolata. Within the same crown layer, the average branch angle was 1.6–2.2 times greater in Luotian, and the angle was directly proportional to crown thickness; (4) the average base diameter and branch length on Luotian were 1.3 cm and 75.8 cm, respectively, and 1.6 cm and 112.2 cm for Lanceolata. For individual trees, branch growth differed significantly (p < 0.01) between Luotian and Lanceolata. However, the lateral branches grew at a similar rate among Luotian trees of different ages; (5) the average height to the lowest live branch on Luotian was 128.3% greater than on Lanceolata, resulting in a significant difference (p < 0.01) in crown size. Compared to the crowns on Lanceolata, the Luotian crowns were 45.3% higher and 41.1% wider, and the surface area, volume, and growth of the crown were 27.0%, 11.4%, and 2.4 times greater than for Lanceolata, respectively; and, (6) the biomass of Luotian and Lanceolata sample trees also differed significantly. The mean crown, branch, and leaf biomass for Luotian was 40.0%, 25.2%, and 54.1% of those for Lanceolata, respectively. However, the leaf biomass in each layer of the Luotian crown was higher than that of Lanceolata, and leaf biomass increased with crown thickness.