Abstract: The results of anatomic observations on secondary xylem of 6 dominant species in a Platycladus orientalis + Broussonetia papyrifera mixed forest in Xiangshan mountain, Huaibei, China, indicated that these species share some xeromorphic features in secondary xylem such as high vessel frequency, less percentage of single porous, thinner vessel, shorter fibers, and lower rays. The availability and safety of the vessel associated with water conduction was evaluated through relative conductivity and the vulnerability index, the result shown that relative conductivity of the 6 dominant species is ordered as Vitex negundo var. cannabifolia, Ziziphus jujuba var. spinosa, Grewia biloba var. parviflora, Broussonetia papyrifera, Cudrania tricuspuidata, Rhamnus parvifolia , while the vulnerability index is ordered as B. papyrifera, V. negundo var. cannabifolia, G. biloba var. parviflora, Z. jujuba var. spinosa, C. tricuspuidata, R. parvifolia, and the availability and safety of water conduction of these plants is coincided with their distribution in Xiangshan mountain. The three widely distributed dominant species, Z. jujuba var. spinosa, V. negundo var. cannabifolia and G. biloba var. parviflora, show great plasticity in some characters, including vessel element length, vessel frequency, relative conductivity, vulnerability index, percentage of single porous, multiserate ray height, multiserate ray width, and single ray height, etc. Compared to those in mixed forest and P. orientalis forest, the species in shrub tend to have shorter vessel elements, higher vessel frequency, less single porous percentage, lower rays, higher relative conductivity, and less vulnerabilityindex, thus indicated that they are inclined to more xeromorphic anatomically. The result from the stepwise multiple regressions show that both of the vessel element length and percentage of single porous increased with the canopy density, and the vessel frequency increased with the wind velocity, multiserate ray width increased with the soil water content.

Key words: Denudation monadnock