Intra- and inter-specific differences in crown architecture in Chinese subtropical mixed-species forests

Abstract

Absorption of photosynthetically active radiation (APAR) is fundamental for tree growth and is strongly influenced by crown architecture. The aim of this study was to quantify the intra- and inter-specific variability in crown architecture in monospecific and mixed-species subtropical Chinese forests. A total of 68 trees, including Castanopsis eyrei, Castanopsis sclerophylla, Cunninghamia lanceolata, Cyclobalanopsis glauca and Liquidambar formosana were destructively sampled and their crown architectures were quantified in terms of the vertical distribution of live branch diameter, individual branch leaf area, leaf area and leaf-area density. The vertical distributions were fitted by a two-parameter right truncated Weibull distribution. Inter-specific variability was assessed using ANCOVA and post hoc Tukey tests and intra-specific variability was assessed by fitting linear and linear mixed effect models. The peak in the vertical distribution of leaf area was highest for the least shade tolerant species, L. formosana (relative depth into the crown of 0.5), intermediate for C. sclerophylla (0.55), C. glauca (0.55) and C. lanceolata (0.6) and lowest for C. eyrei (0.75). For all species, the vertical distribution of leaf area was influenced by tree size except for C. glauca. For L. formosana and C. lanceolata, the distribution of leaf area or branch sizes shifted upwards as tree diameter increased, possibly to overtop neighbouring trees. In contrast, as C. eyrei stem diameter increased, the vertical distribution of mean branch diameter shifted downwards, indicating that larger C. eyrei trees invested a higher proportion of their crown growth into their lower crown when compared to smaller trees. The vertical distribution of leaf-area density varied between species but not within a given species. Crown architectures were not influenced by stand density (basal area) or the species composition of the plot. This intra-specific consistency is useful for modelling light in forests. This study shows that there is a significant inter-specific variability in the crown architectures of the co-occurring species in these subtropical forests. There is also significant intra-specific variability related to tree size and this relationship varies between species. This crown architectural variability and its effect on stand structure are likely to influence the light absorption of these stands.