Leichhardt, land clearing and livestock: the legacy of European agriculture in the Brigalow Belt bioregion of central Queensland, Australia

Abstract

Context The Brigalow Belt bioregion of central Queensland has been extensively developed for agriculture since exploration by Leichhardt in 1844. About 4.5 million hectares of vegetation dominated by brigalow (Acacia harpophylla) was cleared as part of the Land Development Fitzroy Basin Scheme, which commenced in 1962. When the Vegetation Management Act 1999 commenced, 93% of brigalow woodland had been cleared. Grazing is the dominant land use in the Fitzroy Basin, with 2.6 million cattle over 11.1 million hectares (72% of the catchment area). This is the largest cattle herd in any natural resource management region in Australia, accounting for 25% of the state herd and 11% of the national herd. Aims The Fitzroy Basin, Queensland’s largest coastal catchment, drains directly to the Great Barrier Reef, and as reef health continues to decline, there has been increased focus on the impacts of land-use change and grazing management on hydrology and runoff water quality. The Brigalow Catchment Study sought to determine the impact of land clearing, land-use change and land management on hydrology, soil fertility, water quality and animal production in the Fitzroy Basin. Methods The study is a paired, calibrated catchment study. Catchment hydrology, soil fertility, water quality and agricultural productivity were monitored before and after land clearing and land-use change. Key results The Brigalow Catchment Study has shown that clearing brigalow for grazing in the Fitzroy Basin doubled runoff, increased peak runoff rate by 50% and increased total suspended solid loads by 80%. Soil fertility and pasture productivity also declined under grazing compared with brigalow. Overgrazing exacerbated these results, as failure to reduce stocking rate with reduced pasture productivity more than tripled runoff, peak runoff rate and total suspended solid load compared with conservatively grazed pasture. Conclusions This study demonstrates the impacts of land-use change and land management on hydrology, soil fertility and water quality. The long-term data records are a model in their own right, capable of answering land-use and land-management questions beyond the initial study scope. Implications Sustainable grazing management should consider the production limitations of depleted soil and pasture resources to minimise land degradation.