Spatial pattern of regeneration of natural mixed coniferous and natural mixed needle-and broad-leaved forest in Shennongjia

To understand the regeneration characteristics of arbor species in the natural mixed coniferous and natural mixed needle-and broad-leaved forest communities of Shennongjia, we established a 1 hm² forest dynamic monitoring plot in Shennongjia National Park to investigate tree species regeneration, with Ripley's L function used to analyze the spatial distribution pattern, interspecific association, and dominant species. Results showed:(1) 35 752 new individuals were recorded, belonging to 45 species, 29 genera, and 19 families.The dominant species were basically the same as the dominant tree species in the arbor layer. The order of new species was Abies fargesii Franch. > Pinus armandii Franch. > Acer stachyophyllum subsp. tetramerum (Pax) A. E. > Crataegus wilsonii Sarg., thus suggesting the natural mixed coniferous and broad-leaf forest was well renewed. (2) With the increase in plot size, the spatial distribution pattern of regenerated Abies fargesii Franch. and Pinus armandii Franch.changed from a clustered to a uniform distribution, whereas that of Crataegus wilsonii Sarg. and Acer stachyophyllum subsp. tetramerum (Pax) A. E. showed aggregation at the whole scale. This indicated that the regeneration of conifers and broadleaf species showed differentiated spatial ecological utilization strategies. (3) There was a significant positive correlation between Abies fargesii Franch. and the other three dominant regenerated species as well as between Pinus armandii Franch.and Crataegus wilsonii Sarg., thus showing common preferences for microhabitats. The spatial associations between the regeneration of Acer stachyophyllum subsp. tetramerum (Pax) A. E. and Pinus armandii Franch.as well as that between Acer stachyophyllum subsp. tetramerum (Pax) A. E. and Crataegus wilsonii Sarg. were significantly negatively correlated. Thus, competition between species was strong. (4) The spatial distributions of seedlings, saplings, and adult trees of Abies fargesii Franch., Crataegus wilsonii Sarg., and Acer stachyophyllum subsp. tetramerum (Pax) A. E. were significantly positively correlated, which was possibly related to seed propagation limitations. The spatial distributions of seedlings, saplings, and adult trees of Pinus armandii Franch.were negatively correlated at the small scale, and there was asymmetric competition for resources.