A Preliminary Study On The Mechanism Of Maintaining Structure Stability Of Picea Crassifolia Population In The Qilian Mountains

On the basis of the relevant data of the permanent plots in the continuous forest resources inventory system and the typical plots selected and surveyed, using the theories and methods of community ecology and population ecology and referring to the theories of ecosystem stability, the mechanism of maintaining structure stability of Picea crassfolia populations as the constructive tree species of the climax stable communities in the Qilian Mountains has been analyzed. Detailed studies were carried out on the size structure and dynamics of populations density spatial patterns the intraspecific and interspecific competitions and associations of these communities. The results and conclusions are summarized up as follows: (1 )There are four types of size structure of the populations as the increasing type, the stationary type, the mature type and the declining type. The relationship between size structure dynamics of the populations and succession appear to be linear, embodying the tendency toward steady state of the population by self- organization and self-development; on the other hand, some non-linear fluctuation of size structure occurred in the mature and overmature stages, thus embodying the relative steady-state by self-regulation and self-repair of the population. (2) The spatial patterns of the population showed a random type in the Populus +Betula +Picea crass jfolia young forests and a contagious type in both the Picea crass jfolia + Populus +Betula forests and Picea cras4folia forests. The seedling and sapling displayed the contagious distribution comparison among the indices of patches showed that the environmental sieve did not cause the obvious change of the spatial pattern of the population in the process of development from the seedling to the sapling. (3) The spatial pattern analysis of the population showed as follows: The patches?area fluctuated at 100 in2. There are two kinds of patch scale in the young forest, as a countermeasure to relax the intraspecific competition of Picea crassfolia. At any development stage, the spatial pattern of the population showed a intensive contagious type at the 25 m2 of patch scale so that the population realized the self-sustaining by spatial coordination. (4)In the early development periods the population firstly occupied habitats by way of intensive contagious distribution of young trees in high density and then reached a relative stable density at the cost of individuals dead in great numbers. Afterwards the mature and overmature stage, the population presented fluctuation of density in certain extent for maintaining relative stability and dominant status in its entirety. (5)The intraspecific competition of Picea crassfolia populations appeared to be more intensive than interspecific competition with the other species of accompanying trees, and the competition among individuals of neighboring diameter classes was the most intensive in the intraspecific competition; the relation between the competition intensity (CI) and individual diameter at breast height (D) of objective tree followed closely the power functional equation: ChADB; the relation between annual growth (V) of diameter at breast height of objective trees and the competition intensity (CI) also followed the power functional equation: V=ACI8. Picea crassfolia population has the biggest competition ability as a important precondition to form the climax stable community in the region.