The prolonged retention of senescent branches and needles (canopy litter) in Cunninghamia lanceolata canopies is an evolutionary adaptation, yet its impacts on stand microenvironment and understory succession remain poorly quantified. To address this gap, we conducted a 5-year field experiment across six planting densities (1800, 2400, 3000, 3600, 4200, and 4800 trees·ha⁻¹), aiming to evaluate the effects of canopy litter removal on canopy structure, forest light environment, and understory biodiversity. Results demonstrated that leaf area index (LAI) and mean tilt angle of the leaf (MTA) significantly increased with density (p < 0.05), leading to marked reductions in photosynthetic photon flux density (PPFD) and light transmittance (T). Canopy litter removal significantly reduced LAI across all densities after 4–5 years (p < 0.05) and consistently enhanced PPFD and transmittance (p < 0.01). MTA and light quality parameters (red:blue and red:far-red ratios) both exhibited variable responses to litter removal, driven by density and time interactions, with effects diminishing over time. Understory vegetation diversity exhibited pronounced temporal dynamics and density-dependent responses to canopy litter removal, with increases in species richness (S), Simpson diversity (D), and Shannon–Wiener diversity (H), while Pielou Evenness (J) responded more variably. The most notable increase in species richness occurred in the 4th year, when 21 new species were recorded, largely due to the expansion of light-demanding bamboos (e.g., Indocalamus tessellatus and Pleioblastus amarus), heliophilic grasses (e.g., Lophatherum gracile) and pioneer ferns (e.g., Pteris dispar and Microlepia hancei). Correlation analyses confirmed PPFD as a key positive driver of all diversity indices (p < 0.01), whereas LAI was significantly negatively correlated with PPFD, light transmittance, and understory diversity (p < 0.01). These findings demonstrate that strategic management of canopy litter incorporating stand density regulation can improve understory light availability, thereby facilitating heliophilic species recruitment and biodiversity enhancement in subtropical coniferous plantations.

Significant market value discrepancies exist between clear and knotty Chinese fir (Cunninghamia lanceolata) wood, distinguished not only by their aesthetic variations but also by their distinct material properties. This study aimed to explore the differences in physical and mechanical properties between clear and knotty Chinese fir wood. Nine standard trees were chosen from a 26-year-old Chinese fir plantation for the experiment. Subsequent to felling, trunk segments below 7 m in length were transported to the laboratory. For each tree, detailed preparations were made to obtain clear and knotty wood specimens, and these distinct wood specimens were subjected to thorough physical and mechanical assessments. The results revealed significant variations in properties between clear and knotty Chinese fir wood. The shrinkage and swelling coefficients of knotty wood were generally lower than those of clear wood, except for higher radial and tangential air-dry shrinkage. Specifically, the swelling ratio of knotty wood was at least 0.40% lower, and the oven-dry shrinkage was at least 0.58% lower than that of clear wood. Knotty wood exhibited higher air-dry and oven-dry densities, with its density being at least 0.15 g cm⁻³ higher than that of clear wood. However, its mechanical properties, including tensile strength, compression strength, impact bending strength, bending strength, and modulus of elasticity, were lower than those of clear wood. For instance, the tensile strength parallel to the grain of clear wood was 40.63 MPa higher, the modulus of elasticity was 1595 MPa higher, and the impact bending strength was 27.12 kJ m⁻² greater than that of knotty wood. Although the tangential and radial surface hardness of knotty wood increased significantly compared to clear wood, the end hardness remained relatively lower. Overall, knotty Chinese fir wood displayed enhanced physical properties, whereas clear wood showcased superior mechanical properties. Careful selection between clear and knotty wood is recommended based on the specific requirements of wooden structural elements to optimize timber resource utilization.

了解林火对滨海沙地人工林土壤碳氮库的影响，选择滨海沙地上受轻度林火干扰的尾巨桉和木麻黄人工林为研究对象，对比其土壤碳氮储量、可溶性有机碳（DOC）、可溶性有机氮（DON）、微生物量碳（MBC）、微生物量氮（MBN）和矿质氮含量与对照林分之间的差异. 结果显示：轻度林火干扰对滨海沙地木麻黄人工林土壤碳氮库产生显著影响，对尾巨桉影响不显著. 林火干扰3年后，尾巨桉人工林土壤碳储量、氮储量、DOC、MBC与对照林分相比分别升高13.5%、27.7%、2.9%、13.7%，DON、MBN、矿质氮含量分别下降51.3%、14.7%、58.0%，而木麻黄人工林土壤碳储量、氮储量、DOC、DON、MBC、MBN、矿质氮含量分别下降27.9%、24.6%、38.6%、41.1%、24.5%、25.4%、31.7%. 两种人工林的土壤pH值与硝态氮、DON、MBN极显著相关. 本研究表明，轻度林火通过干扰土壤碳氮储量和易变性碳氮，进而对土壤碳氮库产生影响，且这种影响因树种而异. （图3 表3 参45）