Intraspecific Competition in Natural Ulmus pumila var.sabulosa Forests in Hunshandake Sandland

The intraspecific competition in natural Ulmus pumila var.sabulosa forests in the Hunshandake Sandland was quantitatively studied by making use of the method of gradually expanding observation scope and the Hegyi's competition model for individual tree.For Ulmus pumila var.sabulosa community,the optimal competition distance of the objective trees is 8 meters,the intraspecific competition in natural Ulmus pumila var.sabulosa forests gradually become weakened with the diameter classes increasing.The relationship between the competition intensity and the diameter of the objective trees at breast height(DBH)follows a power function and the result predicted by the model reveals that when Ulmus pumila var.sabulosa diameter at breast height is less than 30 cm,the competition intensity change remarkably;and when Ulmus pumila var.sabulosa diameter at breast height is more than 30 cm,the competitions vary little in intensity.It indicates that the method of gradual expanding the scope can effectively determine the scope of the competitive trees and also can reflect the intraspecific competition of natural Ulmus pumila var.sabulosa forests in Hunshandake Sandland.Thinning measure should be adopted to enhance the growth of plants and reinforce the stability of the ecosystem.