Impact of tree clearing on soil attributes for a pastoral property in central Queensland, Australia

Impacts of tree clearing on soil properties in grazing systems of Queensland largely remain undetermined. In the past, most of the landwas cleared to develop pastures to enhance pasture production. The present research highlights how tree clearing affects soil attributes over time on a pastoral property in the semiarid zone of central Queensland,Australia. Paired cleared and uncleared pasture systems were selected to represent three different times since clearing (5, 11–13, and 33 years). Three woodland plant communities, which are common in the region, were studied: poplar box (Eucalyptus populnea), ironbark (Eucalyptus melanophloia), and brigalow (Acacia harpophyllla). Soil macronutrients and micronutrients and exchangeable cations were studied down the profile for 0–5, 5–10, 10–20, 20–30, and 30–60 cm depth. The results suggest that tree clearing initially increased concentration of some nutrients (such as total N in the topsoil) that consequently augmentedpasture production. However, this scenario changes with increased time since clearing: concentrations of some soil nutrients increased, whereas some decreased, thus disturbing the equilibrium in soil functions that further impacts upon pasture yield. The impacts of clearing on soil properties were more apparent at deeper layers of soils. Increase in concentrations of Na at 30–60 cm in cleared pastures of E. populnea and E. melanophloia raises concern for sodicity. Results from this study support other findings in the region that changing native woodlands tointroduced grass pastures is likely to have consequences on soil nutrients, which can affect cattle production gains and the sustainability of pasture systems. (Soil Science 2007;172:516–533)