Leaf economic strategy and stand structural complexity are associated with net woody productivity in a subtropical...

The associations of net woody productivity with biodiversity, functional composition, and stand structure remain poorly resolved in subtropical mixed evergreen-deciduous broad-leaved forests. We used the 2016 and 2021 censuses of 150 contiguous 20 × 20 m subplots in a 6-ha permanent plot at Jinzi Mountain, central China. Net woody productivity was calculated as the annualized net change in live woody biomass. Univariate and multiple linear regressions, random forests, and piecewise structural equation modeling were used to examine relationships with community attributes measured in 2016. Live woody biomass increased from 144.78 to 167.86 t·ha^-1, corresponding to a mean net woody productivity of 4.62 t·ha^-1·yr^-1. Net gains were concentrated in the tree stratum and larger diameter and height classes; classes with a diameter at breast height ≥29 cm accounted for 78.53% of community net woody productivity. In univariate regressions, productivity was positively associated with community-weighted mean (CWM) leaf thickness and negatively associated with CWM specific leaf area and leaf area. Multiple regression also identified species relative-abundance structure and stand structural heterogeneity as significant correlates. In the piecewise structural equation model, species diversity and structural diversity had significant positive direct associations with productivity. A principal component representing higher CWM specific leaf area and leaf area but lower CWM leaf thickness had a significant negative direct association. Functional and phylogenetic diversity had nonsignificant direct paths, although Rao's quadratic entropy was negatively associated with productivity in the multiple regression. These relationships may partly reflect differences in baseline biomass stocks, which were not included as predictors. Retention of healthy large canopy trees, woody-species diversity, and heterogeneous stand structure warrants consideration in close-to-nature forest management, but its consequences for productivity require further testing.