Ecological Analysis of Different Plant Competition Patterns in Community Succession after Forest Fire Disturbance

Taking the naturally regenerated secondary forest after the 1987 fire in the Greater Khingan Range as the study object, this paper systematically analyzed the competition patterns and niche characteristics of two dominant species, Larix gmelinii and Pinus pumila, across different age classes. Through plot surveys and spatial point pattern analysis, combined with the calculation of competition indices and niche breadth, the study revealed significant differences in intra- and interspecific competition between L. gmelinii and P. pumila. The results showed that intraspecific competition dominated for L. gmelinii (accounting for 81.622%), whereas interspecific competition dominated for P. pumila (81.187%). For other non-dominant species, interspecific competition was also predominant. For L. gmelinii, the competition pressure from the same age class exhibited a "rise-then-fall" dynamic pattern with increasing age class, with individuals in age class V experiencing the highest proportion of competition from same-age individuals (28.658%). For P. pumila, intraspecific competition was concentrated in age classes II and III, where the competition intensity from the same age class accounted for 40.502% and 36.215%, respectively. The overall niche overlap among individuals of different age classes was higher for L. gmelinii than for P. pumila, with the highest overlap (0.908) observed between age classes II and III, indicating a strong consistency in resource utilization. In contrast, P. pumila exhibited a generally low niche overlap, suggesting a more differentiated niche structure. For both dominant species, the competition pressure experienced was significantly negatively correlated with their own diameter at breast height (DBH), and the change in competition pressure with age class was relatively gradual for P. pumila.