ON NEIGHBOURHOOD EFFECTS IN A SUCCESSIONAL COMMUNITY AND AN IMPROVED INDEX OF NEIGHBOURHOOD INTERFERENCE
Zhang Dayong, Zhao Songling, Zhang Pengyun, Chen Qingcheng (Ecology Laboratory, Lanzhou University)
This paper deals with the relationship between the growth rate of Picea wilsonii and neighbourhood interference.The significant correlation between Picea individual growth rate and the indices of local interference demonstrates that interference occurs and that the pioneer tree species, Populus davidiana, Betula plat-yphylla,and Picea wi/sonii itself are competitively related with the growth of Picea wilsonii individuals. We are able to account for more than 30% of the variation in plant growth rate of Picea wilsonii as a polynomial function of the size, distance and number of their neighbours within 2 meters.In this study, we have improved the index of neighbourhood interference as follows :where S is the size of subject individual; Si is the size of i-th neighbour; di is the distance to the i-th neighbour; N is the number of neighbours. The improved index can account for 45% of the variation in the growth rate of Picea wilsonii .Since interference occurs and the climax species may establish itself synchronously with the pioneer tree species, it can be reasonably concluded that the main driving force of recovery succession of Picea wilscnii is an interspecies competition among the dominant tree species.