The Subgeneric Composition of Eucalypt Forest Stands in a Region of South-Eastern Australia

Abstract

Pryor's rule that mixed stands of eucalypt forest consist of species from different subgeneric groups was tested statistically using data from a vegetation survey of part of the South Coast of New South Wales. The plot data were stratified by environmental regions, and expressed in terms of the subgeneric combinations of the two most abundant tree species. The categories recognized were the eucalypt subgenera Monocalyptus, Symphyomyrtus and Corymbia, plus Angophora and others. The results suggest that: (a) subgenera are characteristic of certain environmental regions; (b) combinations of subgenera are not random; (c) a modification of Pryor's rule is applicable to three of the four regions studied; and (d) in addition, certain combinations of subgenera occur more frequently than expected by chance, e.g. Monocalyptus occurs as the most abundant species, with Symphomyrtus as subordinate, more frequently than the reverse situation. The results accord with recent reviews of eucalypt forest ecology but there are many plots with a composition of three species from the same subgenus. Biological explanations for Pryor's rule must also take account of these exceptions and the tendency for Symphyomyrtus species to be subdominant to Monocalyptus in the coastal region.