Growth strategies of four subtropical native tree species based on growth processes and biomass allocation

Based on regularly continuous observation data, this study applied the Richard growth model to analyze the growth dynamics of ground diameter (GD) and tree height (H) in plantations of four tree species, Pinus massoniana, Liquidambar formosana, Schima superba, and Elaeocarpus decipiens. Organ biomass allocation was quantified using the harvest method under consistent site conditions, soil characteristics, management measures, and stand ages. Results showed that: (1) The Richard growth model demonstrated excellent predictability and adaptability to the growth dynamics of GD and H across the four tree species plantations. Growth rates varied among species, with P. massoniana demonstrating the highest annual growth rates for GD and H, followed by S. superba, and surpassing those of L. formosana and E. decipiens in the 6th to 8th year. These differences became more pronounced with increasing stand age. Rapid GD growth in P. massoniana occurred earlier (3rd to 8th years) and lasted longer, with H entering its rapid growth phase by the 5th year. In contrast, rapid GD growth for L. formosana, E. decipiens, and S. superba was delayed by 1–2 years and shortened by 2–4 years, with S. superba showing a delayed rapid H growth period and L. formosana and E. decipiens failing to enter a rapid H growth phase. Notably, all species prioritized GD growth, especially P. massoniana. (2) Trunk biomass accounted for the largest proportion of total plant biomass (46.0%–58.8%), with L. formosana having the highest proportion. Leaf biomass contributed the least (3.0%–11.2%), with L. formosana showing the lowest share. Above-ground biomass (AGB) in P. massoniana was significantly greater than its below-ground biomass (RGB), while no significant difference was observed between AGB and RGB in three broad-leaved species. Furthermore, the three broad-leaved species exhibited higher RGB proportions (25.4%–27.6%) and root-to-shoot ratios (35.1%–40.6%) compared to P. massoniana. The biomass allocation in P. massoniana favored AGB, enhancing its competitiveness for above-ground space and light, thereby supporting rapid GD and H growth. In contrast, the distribution of AGB and RGB in the three broad-leaved trees was relatively balanced, resulting in slower GD and H growth rates, especially in E. decipiens, which exhibited well-developed root systems and strong competition for subsurface nutrients. In S. superba, AGB was preferentially allocated to branches and leaves, facilitating fast-growing characteristics, while in L. formosana, trunk biomass allocation promoted H growth. These results highlight the complementary advantages of mixed plantations. Pairing P. massoniana with S. superba enhances the cultivation of large-diameter timber, combining P. massoniana with L. formosana improves soil fertility, and integrating P. massoniana with E. decipiens optimizes resource utilization for sustainable growth.