八大公山常绿落叶阔叶混交林枯立木物种组成、大小级与分布格局

Species composition, size class, and spatial patterns of snags in the Badagongshan(BDGS) mixed evergreen and deciduous broad-leaved forest in central China

枯立木是森林生态系统的重要组成部分,对其数量特征(如物种组成和大小级)与分布格局的研究是认识这个特殊类群的起点。本文以湖南八大公山25 ha森林动态监测样地常绿落叶阔叶混交林为研究对象,以该样地第一次木本植物(DBH≥1 cm)调查数据为基础,分析了枯立木的物种组成、径级结构、分布格局以及生境关联。结果表明,样地内共有枯立木(DBH≥1 cm,高度≥130 cm,完全死亡)8,947株。其中,1 cm≤DBH<5 cm枯立木4,258株(47.59%),5 cm≤DBH<10 cm枯立木2,132株(23.84%),10 cm≤DBH<30 cm枯立木2,377株(26.57%),DBH≥30 cm枯立木180株(2%);平均DBH为8.0 cm,最大DBH为83.5 cm。从分布格局来看,0–50 m的尺度上,样地内枯立木主要呈现聚集分布,但在接近40 m的尺度上,逐渐变为随机分布。利用多元回归树(multivariate regression tree,MRT)将样地生境分为3类,运用Torus转换比较某类生境中枯立木密度与物种零分布模型中的期望密度,结果显示枯立木在山谷中分布较少,山脊较多,而在山坡生境则呈现随机分布。鉴定到种的枯立木有724株(8.1%),隶属于26科84种;其中,杜鹃花科、壳斗科和樟科枯立木最多。在物种水平上,多脉青冈(Cyclobalanopsis multinervis)、长蕊杜鹃(Rhododendron stamineum)和黄丹木姜子(Litsea elongata)枯立木最多;而优势树种亮叶水青冈(Fagus lucida)的枯立木并不多见。

Snag（standing dead tree） is an important component of forest ecosystems. Snag characteristics such as species composition, size class, and spatial patterns correlate with community maintenance mechanisms. Here we examine species composition, size class structure, spatial patterns and habitat associations of snags from a woody plant census of the 25 ha evergreen and deciduous broad-leaved mixed forest dynamics plot of Badagongshan（BDGS）. There were 8,947 snags（DBH ≥ 1 cm, height ≥ 130 cm, totally dead） in the plot; 4,258（47.59%） snags with DBH 1–5 cm, 2,132（23.84%） snags with DBH 5–10 cm, 2,377（26.57%） snags with DBH 10–30 cm, and 180（2%） snags with DBH ≥ 30 cm. The average snag DBH was 8.0 cm and the maximum was 83.5 cm. At the scale of 0–50 m, snags were mostly aggregated in the plot, but changed to random distributed near the scale of 40 m. Habitat was divided into three categories with a MRT（multiva-riate regression tree） analysis. Density of snags was compared to habitat type with expected densities derived from species null distributions with a Torus transformation. Our findings indicate that snags in the BDGS plot were negatively related to valleys, but positively related to ridges, and randomly distributed on slopes. Among all the snags, only 724（8.1%） snags were identified to species level including 84 species（26 families）. At the species level, snags of Cyclobalanopsis multinervis, Rhododendron stamineum and Litsea elongata dominated while snags of Fagus lucida was less common.