Multi-trait evaluation and selection of elite Cunninghamia lanceolata provenances for high-quality, large-diameter and knot-free timber

Cunninghamia lanceolata (Lamb.) Hook. (Chinese fir) is a cornerstone timber species in subtropical China, where market demand is shifting toward large-diameter, knot-free wood with enhanced mechanical properties. However, trees from conventional plantations frequently exhibit excessive knotting and variable wood quality, limiting their high-value applications. To bridge this gap, we performed an integrated multi-trait evaluation of nine 39-year-old provenances, assessing growth, knot morphology, and wood properties. A randomized complete block design was adopted, and measurements were conducted for 23 traits. Provenance effects were significant for 16 traits, highlighting the necessity of long-term trials (≥30 years) for capturing mature phenotypic expression. Importantly, weak correlations between timber yield, knot-free wood proportion, and wood density indicate that these key traits can be improved concurrently. PCA reduced the trait dimensionality to five components explaining 93.69 % of total variance, dominated by wood quality (PC1, 41.36 %) and knot attributes (PC2, 19.42 %). The Bredenkamp index identified three elite provenances (HY, NP, JP) that synergistically enhanced total timber yield (by 0.37 %), knot-free wood proportion (by 9.10 %), and key mechanical properties (by 9.70–15.21 %) relative to the population mean. These provenances constitute optimal germplasm resources for breeding programs dedicated to high-quality, large-diameter, knot-free timber. Our results demonstrate a viable breeding strategy for breaking the traditional growth-quality trade-off in conifers, and provides a robust scientific basis for advancing the genetic improvement and sustainable management of C. lanceolata . • First multi-trait evaluation of 39-year Cunninghamia lanceolata elite provenances for high yield, knot-free wood, and superior wood properties. • Weak trait correlations unlock potential for independent breeding axes targeting productivity and wood properties. • Reveals the necessity of long-term (≥30 years) trials for capturing ontogenetic trait dynamics.