Surface soil chemical and physical patterns in a brigalow–Dawson gum forest, central Queensland

Abstract

AbstractBrigalow (Acacia harpophylla)–Dawson gum (Eucalyptus cambageana) open forests are predominantly supported by solodic soils in central Queensland. This report describes relations between some physical, chemical and morphological properties of surface soils (0–0.10 m) within a virgin brigalow–Dawson gum forest. Soil property gradients were found to radiate horizontally from tree‐dominated to non‐vegetated areas, indicative of a vegetation‐induction process. These reflect the importance of litterfall organic matter in determining soil fertility and soil physical conditions at this site.The decomposition of litterfall is probably responsible for significant increases in soil organic carbon (C), total nitrogen (N) and total sulphur (S) concentrations with increasing vegetation canopy cover. The composition of soil organic matter appears constant across the study area, as similar soil C:N:S ratios were recorded across all vegetation canopy classes. Soil salinity, total phosphorus, mineral nitrogen, cation exchange capacity, exchangeable calcium and exchangeable potassium levels also increased with increasing vegetation canopy cover.Surface soil physical properties were also related to vegetation canopy cover. Bulk density and the < 20 μm dispersion ratio decreased while soil micro‐relief and A hor̀izon depth increased with increasing vegetation canopy cover. Organic C, through inverse relations with bulk density and the < 20 μm dispersion ratio, appears to enhance soil porosity and aggregate stability, indicating the role of organic matter in the stabilization of larger virgin soil aggregates.The close association between virgin forest and surface soil fertility is seen to have implications for changes in land‐use, with a decline in nutrient availability, soil aggregate stability and productivity following forest clearing.