Diameter Structure and Life Table of Ulmus elongata Community in Zhejiang

In August 2021, 8 sample plots of 20 m×30 m were established in Ulmus elongata community in Songyang, Zhejiang province for determination of DBG/ground diameter height of every U. elongata, and DBH, height, quantity of associated tree species, importance value of each tree species was calculated. The results showed that the important value of U. elongata was 57.91%, absolutely dominant tree species in the community. There were also 12 tree species with important value more than 1% at arbor layer such as Cunninghamia lanceolata, Machilus thunbergii, Cyclobalanopsis glauca, Cryptomeria fortunei, Taxus wallichiana var. mairei, Pinus massoniana, Liriodendron chinense, Dalbergia hupeana, Toona sinensis, Celtis sinensis and Liquidambar formosana. U. elongata was clustered distribution, and the diameter structure like inverted J-shaped mode. The individuals of diameter class I (DBH<5 cm, interclass of 5 cm) including seedlings and saplings accounted for 83.1% of the total individuals, but with higher mortality rate in the community. The mortality rate of individuals of diameter class I-III was more than 68.4%, while that of individuals of diameter class IV-VII lower than 35%. The mortality rate of individuals of diameter class VIII increased to 50%, and then steady. The maximal life expectancy of the community occurred at diameter class IX. The investigation demonstrated good natural regeneration of U. elongata community. The survival curve of the community was approximated to the Deevey-Ⅲ model, indicating expanding community. The high mortality of younger individuals was the main cause of rare mature individuals in the community.