Understanding the dual effects of distance and density on tree distributions of Pinus tabuliformis and Picea crassifolia is important for the management of arid forests. Here we studied the spatial arrangement of different-sized conifer trees in two monospecific forests in China’s Luoshan Mountains to better understand their growth dynamics. Our findings showed the following: (1) Young trees (seedlings and saplings) are more clustered than adult trees. (2) Adult Pinus tabuliformis adversely impacted saplings within 2 m, whereas Picea crassifolia showed small-scale facilitation but large-scale competition in its conspecific relationships. (3) At smaller to medium spatial scales, dead adult Picea crassifolia had a stronger positive correlation with seedlings than with saplings. (4) At 9 m, dead Pinus tabuliformis trees were more clustered than live ones. (5) Live Picea crassifolia trees were more clustered than dead ones at distances of 4–12 m. (6) Pinus tabuliformis adults exhibited random patterns against dead seedlings and saplings. The dead Pinus tabuliformis seedlings and saplings showed random mortality patterns. Adult Picea crassifolia trees, by contrast, had significant positive correlations with dead seedlings and saplings at small and intermediate spatial scales. Our study indicates that survival rates of Picea crassifolia seedlings and saplings may be higher when mature trees are less dense. This suggests that thinning could benefit regeneration.
Wang et al. (Tue,) studied this question.