Does the peak time of stand leaf area equal the biological maturity age of forests?

Leaf area is an important eco-physiological variable for quantifying the potential production of trees, since it is closely related to tree growth. The age of biological maturity has been defined as the age of culmination of mean annual increment (MAI), which is one of the bases for determining the reasonable rotation length or rotation age. However, there is no research on the relationship between the peak time of leaf area and biological maturity age. In this study, based on Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook.) plantations in two different subtropical climate zones (i.e., middle-subtropical climate zone of Jiangxi and Hunan provinces versus the northern-subtropical climate zone in Hubei province), the stand leaf area and stand volume were fitted using the nonlinear mixed-effects (NLME) model for exploring the relationship between their growth characteristics and peak time of stand leaf area. The results showed that in different climate zones, the dynamic changes of stand leaf area were all in the form of a single peak. The trends of stand MAI were very close to that of stand leaf area during the process of stand dynamics, and the time to reach the peak was basically the same. The peak time of stand leaf area (Jiangxi: 21 years; Hubei: 21 years; Hunan: 19 years) was highly consistent with the biological maturity age (Jiangxi: 22 years; Hubei: 21 years; Hunan: 20 years). Our findings will provide a theoretical basis for the delimitation of biological maturity age and quantitative management of Chinese fir plantations in different climate zones.