Introduction: Soil microorganisms are the key factors in elucidating the effects of thinning on tree growth performance, but the effects of vegetation and soil on the species composition and function of soil microorganisms after thinning are still not well elaborated.Methods: The effects of thinning on understory vegetation diversity, soil physicochemical properties and soil microbial community composition were investigated in a thinning trial plantation ofCryptomeria japonicavar.sinensis, including four thinning intensities (control: 0%, LIT: 20%, MIT: 30% and HIT: 40%), and the relationships of the microbial community structure with the understory vegetation diversity and soil properties were assessed.Results: The results showed that thinning had a greater effect on the diversity of the shrub layer than the herb layer. The soil bulk density and the contents of soil organic matter, total potassium and nitrogen increased with increasing thinning intensities. The Shannon and Chao indices of soil bacteria and fungi were significantly lower in the LIT, MIT and HIT treatments than in the control. Thinning can significantly increase the abundance ofProteobacteriaandActinobacteria, and higher thinning intensities led to a higher relative abundance ofAscomycotaand a lower relative abundance ofBasidiomycota,Rozellomycota, andMortierellomycota. Redundancy analysis indicated that soil physicochemical properties rather than understory vegetation diversity were the main drivers of microbial communities, and fungi were more sensitive to soil properties than bacteria. Functional prediction showed that thinning significantly reduced the potential risk of human diseases and plant pathogens, and the nitrogen fixation capacity of bacteria was the highest in the HIT treatment. Thinning significantly increased the relative abundance of cellulolysis and soil saprotrophs in bacteria and fungi.Conclusion: The findings provide important insights into the effects of thinning onC. japonicavar.sinensisplantation ecosystems, which is essential for developing thinning strategies to promote their ecological and economic benefits.

Tree growth, along with soil properties, is greatly affected by forest management. We used a typical sampling to study the impact of four thinning intensities (T1: 0%, 2500 stems ha⁻¹; T2: 20%, 2010 stems ha⁻¹; T3: 30%, 1750 stems ha⁻¹; T4: 40%, 1500 stems ha⁻¹) on the tree growth and soil physicochemical properties and their correlation in Cunninghamia lanceolata plantations. The average annual increments in tree height, diameter at breast height (DBH), and volume increased with thinning intensity, and those of T4 differed significantly (P < 0.05) from those of T1. The average annual stand volume increments of T4 were significantly (P < 0.05) lower than that of T1, while the maximum value presented at T3. However, the effect of thinning in promoting the growth of Chinese fir diminished with time. As the thinning intensity increased, the diameter class distribution of the sample stands moved rightwards. Moreover, thinning improved soil physiochemical properties. The effects of thinning on soil properties in 0–20 cm soil layer were greater than those in 20–40 cm soil layer. There was a positive correlation between available nitrogen, available potassium and tree growth. The results of this study showed that thinning had a potential effect on tree growth and soil properties. The heavy thinning intensity (approximately 1500 stems ha⁻¹) was the optimum for maintaining economic and ecological benefits. However, heavy thinning significantly reduced stand volume. From the perspective of improving stand volume and biomass, a moderate thinning intensity (approximately 1750 stems ha⁻¹) could be considered for adoption.

Soil multifunctionality is essential for the enhancement of soil carbon sequestration, but disturbances such as thinning practices can influence soil microbial activity and carbon cycling. Microbial residues, particularly microbial residue carbon (MRC), are important contributors to soil organic carbon (SOC), but the effects of thinning intensity on MRC accumulation remain poorly understood. This study evaluated the impact of four thinning treatments—control (CK, 0%), light-intensity thinning (LIT, 20%), medium-intensity thinning (MIT, 30%), and high-intensity thinning (HIT, 45%)—on soil multifunctionality in Chinese fir plantations five years after thinning. Soil nutrient provision, microbial biomass, enzyme activity, and microbial residue carbon were assessed. The results showed that thinning intensity significantly affected soil nutrient provision and microbial biomass, with MIT and HIT showing higher nutrient levels than CK and LIT. Specifically, MIT’s and HIT’s total nutrient provision increased by 0.04 and 0.15 compared to that of CK. Enzyme activity was highest in LIT (+0.89), followed by MIT (+0.07), with HIT showing a decline (−0.84). Microbial biomass, including bacterial PLFAs (B-PLFAs), fungal PLFAs (F-PLFAs), microbial biomass carbon (MBC), and nitrogen (MBN), was highest in CK and MIT, and lowest in HIT, with MIT showing a 0.13 increase compared to CK. Microbial residue carbon (MRC) accumulation was positively correlated with soil organic carbon (SOC), total nitrogen (TN), available nitrogen (AN), and easily oxidized organic carbon (EOC). The highest MRC content in the 0–20 cm soil layer was observed in MIT and CK (10.46 and 11.66 g/kg, respectively), while the MRC in LIT and HIT was significantly lower, reduced by 24% and 12%, respectively. These findings highlight the significant role of thinning intensity in microbial activity and carbon cycling. Medium-intensity thinning (MIT, 30%) was identified as the most effective approach for promoting microbial biomass and enhancing carbon cycling in Chinese fir forest soils, making it an optimal approach for forest management aimed at increasing soil carbon sequestration.

With the objective of identifying superior Vernicia montana trees grounded in phenotypic and agronomic traits, this study sought to develop and implement a comprehensive evaluation method which would provide a practical foundation for future clonal breeding initiatives. Using the Vernicia montana propagated from seedling forests grown in the Suxian District of Chenzhou City in southern Hunan Province, we conducted pre-selection, primary selection, and re-selection of Vernicia montana forest stands and took the nine trait indices of single-plant fruiting quantity, single-plant fruit yield, disease and pest resistance, fruit ripening consistency, fruit aggregation, fresh fruit single-fruit weight, fresh fruit seed rate, dry seed kernel rate, and seed kernel oil content rate as the optimal evaluation indexes and carried out cluster analysis and a comprehensive evaluation in order to establish a comprehensive evaluation system for superior Vernicia montana trees. The results demonstrated that a three-stage selection process—consisting of pre-selection, primary selection, and re-selection—was conducted using a comprehensive analytical approach. The pre-selection phase relied primarily on sensory evaluation criteria, including fruit count per plant, tree size, tree morphology, and fruit clustering characteristics. Through this rigorous screening process, 60 elite plants were selected. The primary selection was based on phenotypic traits, including single-plant fruit yield, pest and disease resistance, and uniformity of fruit ripening. From this stage, 36 plants were selected. Twenty plants were then selected for re-selection based on key performance indicators, such as fresh fruit weight, fresh fruit seed yield, dry seed kernel yield, and oil content of the seed kernel. Then the re-selected optimal trees were clustered and analyzed into three classes, with 10 plants in class I, 7 plants in class II, and 3 plants in class III. In class I, the top three superior plants exhibited outstanding performance across key traits: their fresh fruit weight per fruit, fresh fruit seed yield, dry seed yield, and seed kernel oil content reached 41.61 g, 42.80%, 62.42%, and 57.72%, respectively. Compared with other groups, these figures showed significant advantages: 1.17, 1.09, 1.12, and 1.02 times the average values of the 20 reselected superior trees; 1.22, 1.19, 1.20, and 1.08 times those of the 36 primary-selected superior trees; and 1.24, 1.25, 1.26, and 1.19 times those of the 60 pre-selected trees. Fruits counts per plant and the number of fruits produced per plant of the best three plants in class I were 885 and 23.38 kg, respectively, which were 1.13 and 1.18 times higher than the average of 20 re-selected superior trees, 1.25 and 1.30 times higher than the average of 36 first-selected superior trees, and 1.51 and 1.58 times higher than the average of 60 pre-selected superior trees. Class I superior trees, especially the top three genotypes, are suitable for use as mother trees for scion collection in grafting. The findings of this study provide a crucial foundation for developing superior clonal varieties of Vernicia montana through selective breeding.

Stand structure affects tree efficiency for a competitive use of resources and largely determines stand productivity and carbon stocks. Consequently, research on individual size and differentiation of stand structures is critical for improving monoculture‐stand productivity and carbon stock. Here, we studied the effects of four thinning intensities (CK: 0%, T1: 20%, T2: 30%, and T3: 40%) in an experimental plantation of Cryptomeria japonica var. sinensis, and assessed the individual differentiation characteristics, diameter class‐frequency distribution, stand productivity, and carbon stocks over 6 years. The results showed that the Gini coefficient decreased with increasing thinning intensity and stand age. Self‐thinning of the C. japonica stands occurred even after thinning, and the self‐thinning rate was relatively high at the age of 10–13 years. For T2 and T3 treatments, the self‐thinning did not occur in the 6th year after thinning. The mean diameter of each treatment increased with increasing stand age, and the normal distribution curve of diameter class frequency gradually shifted to the right, with small changes in the CK treatment and the larger one in treatment T3. Thinning increased the large‐diameter (DBH ≥ 26 cm) timber, especially in T2 and T3 treatments. Stand volume and productivity varied with stand age, with the greatest change in stand volume observed in T3, followed by that in the CK treatment. Stand productivity at different thinning intensities generally decreased and then increased with increasing stand age. Although the carbon stock of individual trees and stand increased with time, the individual trees appeared to have an obviously increasing trend with increasing thinning intensity. The results provided important insights into the implications of designing thinning intensity and timing, and determining the tree‐size class removal to meet specific management objectives.