The regular planting and periodic harvesting of a single tree species are features of plantations, which are associated with a reduction of biodiversity. Such plantations are strongly encouraged to be converted into mixed forests. However, the spatial structure dynamics of plantations during the conversion process are poorly understood. In subtropical regions, thinned forest of Chinese fir (Cunninghamia lanceolata [Lamb.] Hook.) and mixed forest of Chinese fir and Michelia macclurei Dandy are considered two ideal modes of plantation management. In this study, we analyzed the spatial structure dynamics of two forest stands and their six main tree populations over a rotation of 27 years, using spatial point analyses. We found that Chinese fir and M. macclurei had a regular distribution pattern (scale, r = 0-1 m) in the early stages of planting (1993), and Chinese fir maintained this pattern after experiencing self-thinning and selective cutting. In addition, non-planted tree species (i.e., natural regeneration of late-seral species, NRLSS) displayed significantly intraspecific clumping, which resulted in the distribution patterns of the forest stands changing from regular to aggregated (r = 0-5.5, 1-20 m), and the species distribution of mixed forest changed from random to clumped (r = 0-20 m). Moreover, during the management period (1993-2018), individuals were significantly differentiated in terms of size, and some small trees in the thinned forest were aggregated together. For the NRLSS, the diameter at breast height was randomly distributed (r = 0-20 m). Furthermore, Chinese fir and M. macclurei were separated at r = 0-1 m in the planting stage, but any pair of the six main populations in the thinned forest and mixed forest were randomly correlated over a rotation. Finally, the nearest neighbor distance of the stands became shorter after conversion, while the values for Chinese fir increased. After 25 years, the mixed plantation and the thinned plantation had a complex spatial structure. They develop towards natural forests and could be used as a template for future plantation management.

Biogeosciences and Forestry Biogeosciences and Forestry Selection priority for harvested trees according to stand structural indices Yuanfa Li (1) , Gangying Hui (2) , Hongxiang Wang (2) , Gongqiao Zhang (2) , Shaoming Ye (1) The selection of trees to be harvested is a core tenet of uneven-aged forest management; however, few studies have focused on the process of tree selection. A set of stand structural parameters (uniform angle index, W; mingling index, M; dominance index, U) based on tree neighbor-spatial relationships, are particularly suitable for expressing the structural characteristics of forest stands. Such indices were used to parameterize thinning in three plots (a-c, each 100 × 100 m 2) in a Korean pine broad-leaved forest in northeastern China and one plot (h, 70 × 70 m 2) in a pine-oak mixed forest in northwest China. Low-intensity single-tree selection was applied according to the principles of structure-based forest management (SBFM), i.e., to promote high mixture, obvious size differentiation, and random pattern with the aim of improving the overall structure of the managed plots. A group of thinning priority indices (v_ij, k_ij and z_ij) were calculated according to the bivariate distributions of the structural characteristics of harvested trees and stands before harvest. Our results demonstrated that v_ij, k_ij and z_ij adequately describe the spatial relationship between each tree and its nearest neighbors, and their combinations can be efficiently used to set thinning priorities on harvested trees with different structural characteristics. Their application can reduce the subjectivity of the selection process and improve the speed and accuracy of the choice of trees to be harvested in uneven-aged mixed forests.