Abstract:

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 (multivariate 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.

Key words: point pattern analysis, diameter class, habitat association, tree mortality, species composition