神农架天然针阔混交林乔木更新的空间格局

为深入了解神农架天然针阔混交林群落乔木树种的更新特征，于神农架国家公园设置1 hm²森林动态监测样地对树种更新进行调查，利用Ripley的L函数分析优势更新树种的空间分布格局、种间空间关联性以及与大树的空间分布关系。结果显示：（1）更新个体共有35 752株，隶属于19科29属45种。更新优势种基本是乔木层优势树种，物种更新数量表现为：巴山冷杉（Abies fargesii Franch.） > 华山松（Pinus armandii Franch.） > 四蕊槭（Acer stachyophyllum subsp.tetramerum（Pax）A.E.） > 华中山楂（Crataegus wilsonii Sarg.），混交林群落更新良好。（2）随着尺度增加，巴山冷杉、华山松更新空间格局由聚集分布向随机分布和均匀分布发展；华中山楂、四蕊槭更新的空间格局在整个尺度上均为聚集分布，表明针叶、阔叶树种更新在空间生态利用策略上出现分化。（3）巴山冷杉与其余3个优势更新树种、华山松与华中山楂更新呈显著正相关，表现出对微生境的共同喜好；四蕊槭分别与华山松、华中山楂更新的空间关系表现为显著负相关，种间竞争激烈。（4）巴山冷杉、华中山楂、四蕊槭的更新个体与大树的空间分布总体为显著正相关，这可能与种子传播限制相关；华山松幼苗、幼树与大树的空间分布在小尺度上呈负相关，存在资源不对称竞争。

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.