This study aims to understand the status, spatial distribution of Chinese fir king resources nationwide and their relationships with environmental factors.

ArcGIS spatial analysis method was used to study the spatial distribution pattern of Chinese fir kings across the country, and the correlations between their distribution and environmental factors such as altitude and temperature were explored.

There are 278 ancient Chinese fir trees meeting the Chinese fir king standard nationwide, among which 91, 101 and 86 trees meet the national first-, second-, and third-class ancient tree standards respectively. The quantity of Chinese fir king resources varies greatly among different distribution regions in China: 54.32% of Chinese fir kings are distributed in the eastern part of the middle zone, and 38.49% in Fujian Province. There are 18 Chinese fir kings with an age over 1 000 years, 30 with a height over 40 m, 5 with a diameter at breast height (DBH) over 2.1 m, and 24 with a crown width over 20 m. The spatial distribution of Chinese fir kings nationwide exhibits a spatial agglomeration characteristic, with high-density core distribution areas covering the junction of northern Fujian and southern Zhejiang, the junction of Guizhou, Guangxi and Hunan, and western and southern Fujian. The quantity of Chinese fir king resources is negatively correlated with the population density of the distribution area, and positively correlated with the radius of the river buffer zone in the distribution area. Most Chinese fir kings are distributed in low-hotspot areas of traditional villages and regions with an altitude of 600-900 m, and the majority grow on forestlands. The height of Chinese fir kings is significantly correlated with local temperature factors and significantly positively correlated with slope; their DBH is significantly positively correlated with local altitude; their crown width is significantly correlated with local wettest-month rainfall and altitude; and their age is significantly negatively correlated with local annual average temperature and maximum temperature of the warmest month.

Chinese fir kings across China exhibited a spatially clustered distribution, with high-density core areas mainly located in northern Fujian and southern Zhejiang, which are traditional Chinese fir-producing regions. This spatial aggregation reflects the environmental adaptability of Chinese fir and provides valuable references for the conservation of ancient Chinese fir trees and the management of Chinese fir plantations. Moreover, 65.10% of Chinese fir kings were distributed within hotspot areas of traditional villages, further demonstrating that the distinctive awareness of protecting ancient Chinese fir trees, shaped by local people's reverence for these trees, has contributed to their long-term preservation.

To explore the difference of knot characteristics and physical and mechanical properties of Chinese fir wood in different strains and ages, so as to provide scientific basis for screening out non-saving strains of Chinese fir wood suitable for production promotion.

6-year-old and 30-year-old Luotian Chinese fir and yellow Chinese fir plantations of different strains and ages were examined. The average standard wood method was employed for felling and biomass determination. The fallen wood segments were processed into plates, and the joint characteristics as well as the physical and mechanical properties of the wood were ascertained. The disparities of knot characteristics and the physical and mechanical properties of the wood among different strains of Chinese fir plantations were compared.

There were differences in the knot characteristics of different strains of Chinese fir at the same age. The knot volume of Luotian Chinese fir is significantly smaller than that of yellow Chinese fir, and the proportion of no knot is significantly larger than that of yellow Chinese fir. The knot characteristics of Chinese fir at different ages of the same strain were different. The knot volume of 6-year-old Luotian Chinese fir and yellow Chinese fir was significantly lower than that of 30-year-old Chinese fir, and the proportion of no-knot wood was significantly higher than that of 30-year-old Chinese fir. There are differences in physical and mechanical properties of different strains of Chinese fir wood at the same age. The wood density, compressive strength and tensile strength of Luotian fir were significantly higher than those of yellow fir. There are differences in physical and mechanical properties of Chinese fir wood at different ages of the same strain. The total dry density, longitudinal tensile strength, flexure strength and flexure elastic modulus of 6-year old Luotian Chinese fir were significantly lower than those of 30-year old Luotian Chinese fir. There is a correlation between the knot characteristics of Chinese fir and the physical and mechanical properties of wood. The knot radius and knot volume of Chinese fir at the same age are significantly negatively correlated with wood density, compressive strength, tensile strength and bending strength. In Chinese fir wood of the same age stage, knot radius and knot volume exhibited highly significant or significant negative correlations with wood air-dry density, oven-dry density, compressive strength parallel to grain, tensile strength parallel to grain, and bending strength. The Kontfree proportion showed highly significant or significant positive correlations with air-dry density, oven-dry density, and compressive strength parallel to grain.

The knot characteristics and physical and mechanical properties of Chinese fir were different in different strains and ages, and the knot characteristics of Chinese fir were correlated with the physical and mechanical properties of wood.