Brigalow Catchment Study
The Brigalow Catchment Study identifies the impacts of clearing brigalow lands. It started in 1965 and is managed by the department, with support from the Department of Primary Industries and Fisheries.
Located on the Brigalow Research Station between Theodore and Moura, the study area represents the extensive brigalow lands of Queensland and New South Wales (about 40 million hectares).
The study captures data on rainfall and runoff, and changes in water balance, resource condition, sustainability and productivity that occur when brigalow vegetation is cleared for cropping and grazing.
Aims
Originally the study aimed to answer the following questions:
- Will the water balance be affected by replacing a perennial brigalow scrub with a winter-dormant buffel pasture, or with seasonal cropping?
- Will land-use change lead to problems of soil erosion, salinity and nutrient rundown?
- Will cropping and grazing enterprises on these lands remain productive and economically sustainable in the long term?
- What will be the impact on the quality of runoff water from cropping and grazing lands adjacent to the Great Barrier Reef?
- With highly variable seasonal conditions, can such changes be quantified with confidence?
Present aims are to assess:
- the impacts of land use on the amount, location and movement of carbon
- the benefits of best management practices in regard to biodiversity, soil health, and enterprise sustainability in a changing climate.
Method
The Brigalow Catchment Study is a paired catchment study consisting of three catchments of 12 to 17 hectares.
- Stage 1 (1965–81): catchments were calibrated so runoff from catchments 2 and 3 could be estimated from catchment 1 runoff.
- Stage 2 (1982–84): catchment 2 was cleared for cropping and catchment 3 for improved pasture (buffel grass).
- Stage 3 (1984–2004): runoff from cropping and grazing catchments was compared to their predicted uncleared runoff using the stage 1 calibration.
Results
Clearing for cropping doubled runoff, halved grain yield after 23 years, reduced soil organic carbon content by 38 per cent after 21 years, made the soil nitrogen-deficient after 12 years, increased deep drainage, and leached 23 tonnes of salt below the root zone.
Clearing for grazing doubled runoff, halved pasture production after 21 years, reduced live weight gain by 38 per cent after 11 years, maintained the original level of soil organic carbon after 21 years, increased deep drainage, and leached 7 tonnes of salt below the root zone.
Nitrogen was removed from the catchments at a rate of 36.1 kg/ha/year under cropping and 1.6 kg/ha/year under grazing.
Other benefits
Because it is long-term, the Brigalow Catchment Study provides other benefits:
- It was critical in the calibration of the RothC soil carbon model, now part of the Australian Greenhouse Office FullCAM carbon accounting model.
- It was a case study for assessing long-term agronomic experiments (LTAEs) in Australia and developing LTAEs guidelines.
- The site was used in a national reconnaissance survey of soil erosion using the activity of the radioactive isotope caesium-137.
Study data have been used to calibrate and validate various resource process and productivity models, and to assess conservative stocking and grazing pressure in the brigalow region in the long term.
The Queensland Climate Change Centre of Excellence and the QSCAPE modeling program also use Brigalow study data for work on the condition of water and other resources in large catchments as land use and land management practices change over time.
More information
The following fact sheets provide more information:
- Brigalow Catchment Study: overview (PDF, 158K)*
- Brigalow Catchment Study: clearing brigalow increases runoff (PDF, 149K)*
- Brigalow Catchment Study: fertility decline of cleared land (PDF, 173K)*
Study data are available for download.
Enquiries
To find out more or to become involved in the study, telephone (07) 4938 4372 or (07) 4992 9110
* Requires Adobe Reader
Last updated 26 March 2008
