川西王朗亚高山暗针叶林25.2 hm^(2)动态监测样地物种组成与群落结构特征

Community composition and structure in a 25.2 hm^(2) subalpine dark coniferous forest dynamics plot in Wanglang,Sichuan,China

川西亚高山暗针叶林是中国寒温性针叶林的重要代表。以云杉(Picea spp.)和冷杉(Abies spp.)为优势树种的暗针叶林是青藏高原东缘亚高山森林的主体,也是我国长江上游重要的生态屏障。该研究基于川西王朗保护区亚高山暗针叶林25.2hm^(2)动态监测样地的首轮清查数据,分析样地木本植物组成和群落结构特征。依照全球森林观测网络(Forest GEO)的标准技术规范,建立面积为25.2 hm^(2)(700 m×360 m)的暗针叶林固定监测样地,对胸径≥1 cm的木本植物进行挂牌标记、坐标定位、物种鉴定和检尺。主要结果有:样地内共标记独立的木本植物个体56574株,分属15科27属46种,其中针叶树4种,常绿阔叶树6种,落叶阔叶树36种;每hm^(2)个体数≤1的稀有种共13个,占样地物种总数的28.26%,占样地总个体数的0.16%。该群落以针叶树岷江冷杉(A.fargesii var.faxoniana,n=9440)和紫果云杉(P.purpurea,n=1645)为建群种和乔木层优势种,重要值分别占总数的26.03%和10.69%,其单位面积内的胸高断面积分别占总胸高断面积(37.87 m^(2)·hm^(-2))的55.22%和24.84%。落叶阔叶树个体数占比最多(78.48%),其中紫萼山梅花(Philadelphus purpurascens)、红脉忍冬(Lonicera nervosa)、冷地卫矛(Euonymus frigidus)为灌木层主要优势种。常绿阔叶树个体仅268株,均为杜鹃属(Rhododendron)植物。木本植物的径级组成具有典型老龄林特征。单株最大胸径出现在紫果云杉,达到127.07 cm。紫果云杉平均单株胸高断面积(0.14±0.18)m^(2)显著高于岷江冷杉(0.056±0.11)m^(2)。所有标记个体的径级分布呈倒“J”形,表明群落处于稳定和正常生长状态。点格局分析的结果表明5个优势种(重要值占比>5%)均呈聚集分布,但随着空间尺度的增加,物种聚集程度变小,趋向于随机分布。该研究的结果为深入研究川西亚高山暗针叶林的多样性维持与更新机制和该类型森林生态系统的保护与管理提供了基础信息。

Aims Subalpine dark coniferous forests are an important representative of the cold-temperate coniferous forests in China.Dark coniferous forests dominated by spruce(Picea spp.)and fir(Abies spp.)are the main body of subalpine forests on the eastern edge of the Qingzang Plateau and an important ecological defense in the upper reaches of the Yangtze River in China.In this study,we examined the community composition and structure of such a dark coniferous forest based on the first census data of the 25.2 hm^(2) Wanglang forest dynamics plot in western Sichuan.Methods The plot was established following the standard protocol of Forest Global Earth Observation Network(Forest GEO)and all free-standing stems with diameter at breast height(DBH)≥1 cm were tagged,mapped,measured and identified to species.Important findings A total of 56574 individuals belonging to 46 species,27 genera and 15 families are tagged,including 4 coniferous species,6 evergreen broad-leaved species and 36 deciduous broad-leaved species.There are 13 rare species(≤1 individuals per hm^(2)),accounting for 28.26%of the total number of species and 0.16%of the total number of individuals in the plot.Abies fargesii var.faxoniana(9440 individuals)and P.purpurea(1645 individuals)are the dominant and constructive species in canopy,accounting for 26.03%and 10.69%of the total importance value,and 55.22%and 24.84%of the total basal area(37.87 m^(2)·hm^(-2)),respectively.The number of individuals of deciduous broad-leaved species accounted for 78.48%of the total individuals.Among them,Philadelphus purpurascens,Lonicera nervosa and Euonymus frigidus are the dominant species in shrub layer.The number of individuals of evergreen broad-leaved species is 268,and all these species belong to genus Rhododendron.The composition of the size distribution shows typical characteristics of old-growth forests.Picea purpurea is the largest tree species(max DBH=127.07 cm)and the mean basal area(0.14±0.18)m^(2) is much higher than that of A.fargesii var.faxoniana(0.056±0.11)m^(2).The size class distribution of all woody species shows an inverse J-shaped distribution,indicating that the community is in a stable and healthy recruitment state.Results of the point pattern analysis reveal that the five dominant tree species(important values≥5)all show aggregated distribution patterns.However,as the spatial scale increases,all five species tend to be randomly distributed.The results of this study provide basic information for future studies on the diversity maintenance and regeneration mechanisms of subalpine dark coniferous forests in western Sichuan,and the conservation and management of this unique forest ecosystem.