Quantitative relationships of intra- and interspecific competition of Platycladus orientalis plantation in Beijing Xishan National Forest Park

In order to investigate the growth status and structure of middle and young stands of Platycladus orientalis plantation in the Beijing Xishan National Forest Park, the intra- and interspecific competition intensity was analyzed between target and competitive tree species using the Hegyi’s competition index (CI). The results showed that 1) the competition intensity increment of middle and young P. orientalis stands became smaller with the increasing distance between species, indicating that the optimal competition distance of the target trees is 6 m. 2) Within the optimal competition distance, the competition stress to the middle and young stands mainly came from the interspecific competition, which accounted for 73.03 percent of the total; the intraspecific competition was weak, accounting for 26.97 percent of the total competition. The most competitive species with P. orientalis was natural renewal Robinia pseudoacacia. The competitive intensity between P. orientalis and R. pseudoacacia reached maximum within 4 m limits. Thus in order to avoid intensive competition, the interval distance of mixed forest of P. orientalis and R. pseudoacacia should be set above 4 m. 3) The competition intensity of P. orientalis became declined with the increase of DBH and the stress reached the maximum when DBH of target trees was less than 15 cm. The relationship between competition intensity and DBH of the target trees followed the relationship of power function.