Effects of competition, resource availability and invertebrates on tree seedling establishment

Abstract

Summary We studied the establishment of tree seedlings in Mediterranean‐type old fields in South Australia in different biotic environments and under different levels of resource availability. Specifically we wanted to: (a) test for a logarithmic relationship between the relative intensity of competition (RCI) and resource availability; (b) assess the potential of confounding resource competition with invertebrate herbivory; and (c) assess whether the architecture of the plant community had any qualitative or quantitative effects upon the relationship between resource availability and RCI. Our glasshouse experiment showed that RCI increased with resource availability at low levels of resources, but not at higher levels, consistent with a logarithmic relationship. The effects of resource competition and invertebrate herbivory were heavily confounded in the field experiment. Plant architecture significantly affected the behaviour and abundance of invertebrates and we therefore conclude that it has the potential to modify the relationship between resource availability and competitive intensity. Although the habitat templet/C‐S‐R model appears reasonably robust, modification of its general framework may be required because one of its basic underlying assumptions is most accurate when competition is defined phenomenologically.