Abstract: Woody debris is a key component of forest ecosystem, and the physicochemical properties are important for its decomposition. In this study, we examined the effects of stand type, decay grade, diameter class, and their interaction on the physicochemical properties of woody debris of Tsuga longibracteata in four different stands in Tianbaoyan National Nature Reserve. Woody debris was classified into five decay grades and four diameter classes. The results showed that wood density of woody debris in T. longibracteata forests decreased with the increased decay grade, but moisture content increased. The diameter class had a significant effect on moisture content of woody debris only in the T. longibracteata pure forest. The interaction of decay grade and diameter class had no significant effect on the physical properties of woody debris in each stand. In terms of chemical properties, decay grade did not affect C content of woody debris, but significantly affected N content and C/N ratio of woody debris in three mixed forests. The diameter class had significant effects on P content of woody debris in the T. longibracteata pure forest and P content and C/N in the T. longibracteata+Rhododendron simiarum mixed forest. The interaction had no significant effect on the chemical composition of the woody debris across all stand types.Wood density was closely correlated with C and P contents of woody debris in the T. longibracteata+R. simiarum mixed forest, as well as C, N, P contents and C/N in the T. longibracteata+Phyllostachys edulis mixed forest. Moisture content had significant correlation with N, P, C/N of woody debris in the T. longibracteatapure forest and P, C/N in the T. longibracteata+P. edulis mixed forest. In conclusion, the physical properties of woody debris are important factors affecting nutrient content.

Key words: Tsuga longibracteata forest, woody debris, decay grade, diameter class, physicochemical property.