Comparative analysis on the growth law and main wood properties of Castanopsis fargesii and Castanopsis hystrix in the southern subtropical region of China

To investigate the differences in growth law and physico-chemical properties of wood between Castanopsis fargesii and Castanopsis hystrix, and to provide a scientific basis for sustainable management and wood utilization of their plantations.

Sixteen-year-old C. fargesii and C. hystrix plantations, with similar site conditions in the southern subtropical region of China, were selected as subjects. Eight dominant trees were felled in each stand, and a comparative analysis was conducted to examine the growth patterns of key tree measurement factors, as well as the differences in wood density, fiber morphology, chemical composition, and chemical properties.

1) The growth trends in diameter at breast height (DBH), tree height, and individual tree volume of Castanopsis fargesii and Castanopsis hystrix were similar, but from the 7th, 15th, and 8th year, the total growth of DBH, tree height, and individual tree volume of C. fargesii was significantly higher than that of C. hystrix (P<0.05). There were no significant differences in the experimental form factors of the trunks between the two species, and their trends were similar. From the 12th year onward, the dominant height of both species significantly surpassed that of similarly aged Pinus massoniana and Cunninghamia lanceolata with similar site conditions; 2) The air-dry density (0.498 g/cm³) and basic density (0.446 g/cm³) of C. fargesii were significantly lower than those of C. hystrix (air-dry density 0.569 g/cm³ and basic density 0.464 g/cm³). There were no significant differences between the two species in fiber length, fiber length-width ratio, and fiber lumen diameter, but there were significant differences in fiber width, fiber wall thickness, wall lumen ratio, and lumen diameter ratio (P<0.05); 3) In the middle age stage, the wood density indices and fiber morphological indices of both species met the requirements for high-quality raw materials for papermaking and fiberboard production. The pH values of the heartwood and sapwood of C. fargesii and C. hystrix were within the suitable range for adhesive curing; 4) The holocellulose content, α-cellulose content, and hemicellulose content of C. fargesii were higher than those of C. hystrix, while the lignin content was lower; 5) The cold water extractives content of the heartwood and sapwood of the two species did not differ significantly, but the hot water extractives, 1% NaOH extractives, and ethanol-benzene extractives contents of C. fargesii wood were significantly higher than those of C. hystrix.

1) Compared to C. hystrix, C. fargesii demonstrates a significant fast-growing rate and is suitable for cultivation as a local precious fast-growing forest; 2) During the middle-aged stage, the relationship between C. hystrix and Betula alnoides in their mixed forest of the same age is mutually beneficial; 3) C. fargesii should not be mixed with relatively slow-growing sun-preferring such as Pinus massoniana. C. fargesii is appropriate for management as general-purpose timber in medium- to short-rotation cycles, including applications such as pulpwood, fiberboard, plywood, and common solid wood products, as well as for producing high-value veneer materials. 4) In contrast, C. hystrix, characterized by its relatively slower growth, is better suited for long-rotation management aimed at producing high-quality, large-diameter timber and high-value veneer materials.