Objective  In the low-quality and low-efficiency Pinus massoniana secondary forest in Cili County, Hunan Province of central China, the niche characteristics of seedlings under different-sized forest gaps during the early stage of gap phase were analyzed and compared to grasp the niche law of forest gap regeneration, and explore the technology of artificial promotion of natural regeneration.

  Method  The ecological community survey method was used to investigate the characteristics of forest gap. Niche characteristics of dominant shrub layer species in Pinus massoniana secondary forest during gap vegetation regeneration were analyzed.

  Result  (1) At the initial stage of gap regeneration, the species and number of plants in the shrub layer in the gap were increased compared with those in the forest. The ranking of important values of dominant tree species in the shrub layer was significantly different. Positive tree species such as Rhus chinensis, Loropetalum chinense, Myrsine africana were ranked higher in the gap. (2) During the early stage, the niche breadth values of the plants in different-sized gaps appeared differentiation. The ecological width of Rhus chinensis, Broussonetia kaempferi, Rubus corchorifolius etc. all showed such a pattern (medium gap > large gap > small gap = the understory). Other plants were not sensitive to the forest gap. (3) The species with niche overlap values (> 0.1) accounted for 85.71%, 92.98%, 44.64 and 12.5% of the species in the large forest gaps (445−480 m²), medium forest gaps (150−180 m²), small forest gaps (68−85 m²) and the understory, respectively.

  Conclusion  Gap size has a certain effect on plant regeneration, and the niche characteristics of plant seedlings are different under different gap area. In the medium gap (150−180 m²), the ecological overlap of regeneration seedlings in Pinus massoniana secondary forest is large. All species could make relatively balanced and effective use of environmental resources, and the regeneration situation is good and stable, which promotes the natural regeneration of the Pinus massoniana secondary forest. It is beneficial to the conservation of biodiversity and the improvement of forest carbon storage of Pinus massoniana secondary forest.