Evaluation of the effects of tree clearing over time on soil properties, pasture composition and productivity

Tree clearing is practised for greater beef production and hence monetary gains from grazing systems of central Queensland. The high rates of clearing in the past and even recently (577,000 ha/yr during 1999-2001) were mainly to develop land for pastures. The sustainability of cleared pasture systems over the long-term is questioned.

Three major types of tree communities i.e. Eucalyptus populnea F. Muell., E. melanophloia F. Muell. and Acacia harpophylla F. Muell.ex. Benth. were selected on one property in central Queensland to quantify theimpacts of clearing on pasture production and composition, and soil properties.The impacts were measured over time-since-clearing (recent (<5 years),medium(11-13 years) and old (>30 years)) in unreplicated cleared pastures in comparison to their replicated uncleared/intact woodland pastures of each tree community.

Measures of pasture above-ground biomass production on asingle property over time-since-clearing in cleared systems showed that gainswere not sustained over the long-term. The difference in response to clearingbetween tree communities was evident and important to support the future policydecisions. The impact of clearing on soil properties (physicochemical andbiological) was confirmed, and explained the lesser availability of nutrientswith time of clearing in cleared pastures. The changes in some soil propertiesunderscored the associated risks and changes in ecosystem functions due toclearing. Less litter was produced at cleared than uncleared pastures, but nutrientrelease was faster at cleared compared to uncleared systems. The overall effectof clearing in terms of pasture and litter production, and major soilparameters were analysed using multivariate analyses.