鄂西南两个自然保护区亚热带常绿落叶阔叶混交林类型及其常绿和落叶物种组成结构分析

Quantitative classification of the subtropical evergreen-deciduous broadleaved mixed forest and the deciduous and evergreen species composition structure across two national nature reserves in the southwest of Hubei, China

为深入研究亚热带常绿落叶阔叶混交林的生物多样性维持机制,合理保护与利用此类森林植被,以鄂西南两个自然保护区——星斗山和木林子典型的亚热带常绿落叶阔叶混交林为研究对象,在野外样方调查的基础上进行了群落数量分类和排序,分析了常绿和落叶物种比例随群落类型及环境因子变化的规律。研究结果表明:(1)将鄂西南两个自然保护区的亚热带常绿落叶阔叶混交林划分为5个群落类型:即青冈-翅柃+尖连蕊茶(Cyclobalanopsis glauca-Eurya alata+Camellia cuspidata)群落(I)、川陕鹅耳枥+青冈-翅柃(Carpinus fargesiana+Cyclobalanopsis glauca-Eurya alata)群落(II)、川陕鹅耳枥+青冈-水马桑(Carpinus fargesiana+Cyclobalanopsis glauca-Weigela japonica)群落(III)、光叶水青冈+多脉青冈-翅柃(Fagus lucida+Cyclobalanopsis multinervis-Eurya alata)群落(IV)和川陕鹅耳枥+交让木+包果柯-翅柃(Carpinus fargesiana+Daphniphyllum macropodum+Lithocarpus cleistocarpus-Eurya alata)群落(V);(2)常绿和落叶物种的丰富度、多度、胸高断面积及重要值等指标随群落类型而变化。在群落II、III和V中落叶物种占优势,而在群落I和IV中二者无显著差异;(3)各类型群落在小径级(1–5cm)内落叶物种的丰富度大于常绿物种,但多度、胸高断面积和重要值大都小于常绿物种。在中径级(5–10 cm)内,群落I和群落IV的各项指标都表现为常绿物种大于落叶物种,而群落II、群落III和群落V的则相反。在大径级(≥10 cm)内,各群落类型的落叶物种都占显著优势,其各项指标大于常绿物种;(4)海拔、坡度、坡向、土壤氮含量和土壤磷含量是影响各群落类型内常绿和落叶物种比例变化的主导因子。

Aims The subtropical evergreen-deciduous broadleaved mixed forest is the largest extant natural vegetation type in southwest Hubei. However, little knowledge exists on the types and compositions（especially the relative ratios of evergreen versus deciduous species） of this forest vegetation. Here, we quantitatively classify the less studied forest vegetation into different community types, compare their size and composition structure, and analyze species-environment relationships which is the basis for further understanding the biodiversity maintenance mechanism and reasonable protection and utilization of this forest. Methods We established 92 20 m × 20 m plots of subtropical evergreen-deciduous broadleaved mixed forest in two national nature reserves in Enshi, Hubei Province, China. All species with stems ≥1 cm diameter at breast height（DBH） in each plot were identified and mapped. These plots were classified by using two-way indicator species analysis（TWINSPAN） and detrended correspondence analysis（DCA）. The species richness, abundance, basal area and importance value were chosen to compare structure, species composition and evergreen anddeciduous ratio. Permutation-based multiple regression on distance matrices and multiple stepwise regression analysis were used to examine the relationship between species distribution and environmental factors. Important findings Our results showed that the subtropical evergreen-deciduous broadleaved mixed forest in the southwest of Hubei could be classified into five community types based on quantitative methods： i.e. Cyclobalanopsis glauca-Eurya alata ＋ Camellia cuspidate（community type I）, Carpinus fargesiana ＋ Cyclobalanopsis glauca-Eurya alata（community type II）, Carpinus fargesiana ＋ Cyclobalanopsis glauca-Weigela japonica（community type III）, Fagus lucida ＋ Cyclobalanopsis multinervis-Eurya alata（community type IV） and Carpinus fargesiana ＋ Daphniphyllum macropodum ＋ Lithocarpus cleistocarpus-Eurya alata（community type V）. Species richness, abundance, basal area and importance value of evergreen and deciduous species in each community types were different. Deciduous species in community II, community III and community V were significantly higher than evergreen species in terms of species richness, stem abundance, basal area and importance value, but they had no significant differences in community I and community IV. The richness of deciduous species in most community types were higher than those of evergreen species, meanwhile the abundance, basal area and importance value of deciduous species in the small size classes（1 cm ≤ DBH 5 cm） in each community types were lower than those of evergreen species. In middle size classes（5 cm ≤ DBH 10 cm）, the richness, abundance, basal area and importance value of deciduous species were higher than those of evergreen species in community II, community III and community V. However, in community I and community IV, the evergreen species were larger than deciduous species in the four indexes. The richness of deciduous species in majority of the community types were higher than those of evergreen species in large size classes（DBH ≥ 10 cm）. The elevation, slope and aspect, soil total nitrogen content, soil total phosphorus content, soil available nitrogen content and soil available phosphorus content were the major factors affecting evergreen and deciduous species distribution across the five community types.