浙江省典型天然次生林主要树种空间分布格局及其关联性

摘要

松阔混交林和常绿阔叶林是亚热带地区天然次生林代表性的森林类型,通过研究主要树种分布变动趋势,可以有效地指导森林经营措施.在该地区4个1 hm2典型样地,在0-30m尺度范围内综合分析了主要树种的空间分布格局及种间关联性,并对同一树种分发育阶段在不同森林群落中的种群空间分布格局进行了比较,以探讨亚热带地区天然次生林群落空间格局形成和种群维持机制.样地1和2为松阔混交林,其中样地1的马尾松密度较低,样地3和4为常绿阔叶林.研究结果表明:(1)以完全随机模型为零假设时,样地1的主要种群在小尺度(＜10 m)呈聚集分布,随尺度增加呈随机分布;样地2-4的主要种群在所有尺度呈聚集分布,随尺度增加聚集强度逐渐减弱;以异质泊松模型为零假设时,4个样地的主要种群在大部分尺度呈随机分布;(2)青冈和苦槠的小树(5.0 cm≤DBH＜10.0 cm)在4样地的所有尺度以聚集分布为主,大树(DBH≥10.0 cm)在松阔混交林样地呈随机分布趋势,但在常绿阔叶林样地青冈在0-20 m尺度、苦槠在所有尺度呈聚集分布;(3)松阔混交林中建群种马尾松和其他树种的种间关联性,在样地1的小尺度为负相关,随尺度增加为不相关,在样地2的所有尺度为负相关;常绿阔叶林中建群种青冈和其他树种的种间关联性在在样地3的小尺度为负相关,随尺度增加为不相关,在样地4的所有尺度为负相关;所有伴生树种的种间关联性以负相关为主.结果说明,种群空间分布格局及其关联性随群落结构和空间尺度的不同而出现变化,在松阔混交林和常绿阔叶林群落格局形成中除了扩散限制和生境异质性以外,密度制约机制在松阔混交林中发挥了重要作用,而在常绿阔叶林中其作用随着树木生活史阶段的提高而减弱.%Mixed broadleaf-conifer forests and broadleaf forests are the main forest type in subtropical region.Understanding the spatial distribution of dominant tree species among these forest types can provide insights for effective forest management measures and the mechanisms of community assembly in subtropical forests.In this study,we examined the distributions and associations of dominant species with different life stages in mixed broadleaf-conifer forests and broadleaf forests separately.We established four 1 hm2 forest plots,including two in mixed forest (plots 1 and 2) and two in broadleaf forests (plot 3 and 4),to detect species associations and distributions.All trees with diameter at breast height (DBH) ≥ 5 cm were mapped and identified.For mixed-forest plots,the density of Pinus massoniana was lower in plot 1 than in plot 2.We applied spatial point pattern analysis in this study,and the spatial distribution of dominant tree species and associations of different species were analyzed.The results showed that (Ⅰ) When using a complete spatial randomness null model,most populations in plot 1 showed aggregated distribution at smaller scales (＜ 10 m) and random distributions at larger scales.However,in plots 2-4,most populations showed an aggregated distribution at all scales.In addition,when using a heterogeneous poisson null model,most populations in all plots showed random distributions at all scales;(Ⅱ) Small trees (5.0 cm ＜ DBH ＜ 10.0 cm) of Cyclobalanopsis glauca and Castanopsis sclerophylla showed aggregated distribution in all plots,whereas large trees (DBH ＞ 10.0 cm) showed random distribution in plot 1 and 2 and aggregated distribution in plot 3 and 4;(Ⅲ) P.massoniana was negatively associated with other species at smaller scales in plot 1,and at all scales in plot 2.C.glauca was negatively associated with other species at smaller scales in plot 3,and at all scales in plot 4.All species showed negative associations at all scales.In conclusion,the spatial distribution and associations of tree species showed different patterns in the two forest types.These results indicated that the spatial distributions and associations of trees were regulated by dispersal limitation and environmental heterogeneity in mixed forest and evergreen broadleaf forest.Moreover,density dependence played an important role in mixed forests and the effects of density dependence tended to decrease along the life stages of trees.