Diameter Structural Distribution of Coniferous Mixed Near-Mature Forest in Fujian Province

In 2022, at the Laizhou Experimental Center of Yangkou state-owned Forest Farm in Fujian Province, we studied the diameter at breast height (DBH) distribution characteristics of 23-year-old mixed coniferous forests comprising four conifer species (Chamaecyparis formosensis, Calocedrus formosana, Cunninghamia lanceolata, and Fokienia hodginsii) using skewness (Cs), kurtosis (K), and the coefficient of variation (C) as indicators.We used six probability density functions(normal distribution, log-normal distribution, Weibull distribution, gamma distribution, growth distribution and negative exponential distribution)in combination with the chi-square(χ²)test to analyze the DBH distribution patterns.The results showed that the average DBH of the mixed coniferous forests of the four species at 23 years old was 17.25 cm, ranging from 5.5 cm to 32.2 cm, with a predominance of trees in the middle diameter class.The main DBH distribution of the stands was between 11 cm and 23 cm, with a cumulative percentage of trees exceeding 77%.Among the six distribution functions, the Logistic distribution showed the best fit and highest accuracy, accurately describing the DBH distribution pattern of mixed coniferous forests.Adjusting the tree number distribution according to the Logistic distribution function may have some reference value for improving stand quality and enhancing forestland productivity.