Climate-sensitive tree height–diameter allometry for Chinese fir in southern China

Tree height–diameter allometry is crucial in regulating forest ecosystem structure and estimating biomass and carbon storage. Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) is the most widely planted tree species across subtropical China. Yet our understanding of how height–diameter allometry of Chinese fir relates to climate over different sites is limited. Remeasured data of 60 plots were used to explore height–diameter allometry of Chinese fir in relation to climate using a three-level NLME approach. The data consisted of five initial planting densities distributed in Fujian, Jiangxi, Guangxi and Sichuan provinces (sites) in subtropical China. Results showed that tree heights increased with increasing mean annual temperature (MAT) and mean warmest month temperature (MWMT) and decreased with increasing annual heat–moisture index (AHM) and summer mean maximum temperature (SMMT). The contribution of MAT to height–diameter allometry was larger than AHM, SMMT and MWMT, which suggested that temperature was a key climate factor that shapes height–diameter allometry of Chinese fir in subtropical China. Trees planted at a higher density level of 6667–10 000 trees ha−1 were slenderer than those planted at a lower density level of 1667–5000 trees ha−1. The scale of height–diameter allometry of Chinese fir nearly held constant in the four sites and was close to 0.5 predicted by the stress-similarity model. Our results will help further understanding of the climate sensitivity affecting the height–diameter allometry of Chinese fir plantations.