Competition from neighboring trees in eucalyptus monoculture and in mixed species native forest restoration plantations.

摘要

Competition has been recognized as a crucial factor in determining stand structure and productivity. However, competition is not a simple pattern. Its intensity and importance vary with structures of neighboring tree size and composition, and nutrient gradients. Our studies examined the influence of neighborhood uniformity on growth of individual trees in Eucalyptus monoculture, and competition between pioneer and non-pioneer species in mixed native species restoration plantations by developing a number of alternative neighborhood growth models. Our analyses showed that neighborhood uniformity of tree sizes had significant effects on growth of individual clonal Eucalyptus trees and these effects increased with increasing age of stand because stand and neighborhood tree size became less uniform with age. For competition from pioneer trees to non-pioneer trees, competition from neighboring trees had strong effects on the growth of individual non-pioneer trees, and the intensity of competition from neighboring trees varied with focal tree species guild and degrees of silviculture interventions. For example, non-pioneer legumes experienced competition as a function of neighboring tree sizes and distances only. Non-pioneer non-legumes experienced competition as a function of neighboring tree sizes and distances, and also by the identity of neighboring species guilds. The non-pioneer non-legumes experienced stronger competition in the intensive silviculture treatment, probably resulting from the neighboring species guild of pioneer non-legumes, unlike the non-pioneer legumes. Although intensive silviculture initially enhanced forest stand productivity (both density and tree size), strong competition from fast-growing lowered the later growth of individual non-pioneer trees. Our analyses suggested implications to: (i) increase and maintain stand uniformity to increase stand stem productivity and quality; and (ii) control strong, even exclusive completion in some cases from pioneer trees to non-pioneer trees through matching species to be mixed and managing their abundance.