The Nature of Soils under Blackbutt and Flooded Gum Forest Communities near Coffs Harbour, N.S.W

Abstract

The nature of the forest soils under a lower slope, wet sclerophyll, flooded gum ('Eucalyptus grandis') forest community and an upper slope, dry sclerophyll, blackbutt ('E. pilularis') forest community was studied near Coffs Harbour, New South Wales. The relationship of changes in the spatial distribution of the soil properties beneath a large flooded gum and two large blackbutt trees were analysed to determine what properties of the soil were dependent upon the influence of the forest vegetation, especially the presence of the individual trees and how variable were the distribution of these properties. 14 soil profiles were described and their mineralogical, morphological, physical and chemical properties characterized from pits excavated radial to the boles of the large blackbutt and flooded gum trees. Differences in the morphological soil horizons of the pit sections were recorded graphically by visual and photographic observations. Additional data were obtained from soil cores sampled on a grid pattern over the faces of the pits and forest litter transects radial to the eucalypt boles. ... The spatial variation of soil properties about the large eucalypts were interpreted as indicating the effect of the forest trees in influencing the distribution and impact of forest pedogenetic factors such as organic matter, tree roots and forest organisms, about their boles. Concentrations of stemflow water, differential litter accumulation, root pedoturbation and the mechanical pressures of the tree combined to produce one form of soil morphology associated with the tree boles while increased pedoturbation by soil fauna, especially earthworms, (flooded gum site) or the shallowness of the solum (blackbutt site) produced a differing soil morphology away from the eucalypts. Therefore this study provides evidence for the hypothesis that the individual trees of different forest communities can induce spatial heterogeneity in soil chemical, physical and morphological properties, and that the nature of these patterns are dependent upon features of the soil landscape (depth of solum, soil texture etc.) and the particular nature of the tree species. This latter factor causes the spatial soil patterning to be dynamic and stochastic in its development.