Image of a paddock with rows of a crop with Brigalow trees in the background

Brigalow trees compete with crops for water and nutrients.

Recovering biodiversity and promoting sustainable agriculture in the Queensland Brigalow Belt

Dr Melanie Bradley undertook doctoral research in the southern Queensland Brigalow Belt, to investigate opportunities for integrating brigalow vegetation with dryland cropping.

  • 17 March 2009 | Updated 14 October 2011

Introduction

Native brigalow vegetation coverage has been reduced by more than 90 per cent in the Queensland Brigalow Belt, leading to concerns about land and water degradation and biodiversity loss.

Potential exists for avoiding resource degradation, recovering biodiversity and promoting sustainable agriculture, by deliberately integrating regrowth and mature stands of brigalow vegetation with dryland cropping systems.

During 2003–06 Dr Melanie Bradley completed a Doctorate project in the southern Queensland Brigalow Belt, to look at different aspects of integrating brigalow conservation with cropping.

The research was supported by CSIRO and Griffith University, Queensland, Australia. It investigated:

  • tree-crop competition – to calculate the yield loss that occurs when trees are retained in an agricultural landscape
  • soil chloride profiles under annual cropping and brigalow vegetation – to discover whether deep drainage had increased and chloride leaching had occurred, following land-clearing
  • the biodiversity values of regrowth and mature brigalow vegetation – to determine effective ways of promoting biodiversity recovery.
“The best ecological and economic outcomes will be achieved by retaining both regrowth and mature brigalow vegetation in the landscape.”
Dr Melanie Bradley, CSIRO

Major findings

Tree-crop competition

  • there was no evidence of tree-crop competition adjacent to young (4 years old) brigalow regrowth
  • at sites with older regrowth (11–20 years) and mature brigalow vegetation, tree-crop competition zones ranged from 12–47 m
  • wheat yields in the competition zone were reduced, on average, by 46–98 per cent, compared to wheat yields in the open paddock (i.e. the area beyond the influence of the trees)
  • future research should investigate how land management practices, climatic conditions, vegetation clearing and cropping history, impact on tree-crop competition.

Soil chloride and deep drainage

  • higher soil chloride levels were measured under brigalow vegetation, in comparison to the levels measured under cropping, providing evidence that deep drainage had increased and chloride had leached, following land clearing
  • the drainage rate under cropping needs to be quantified and compared with drainage rates under brigalow vegetation, and assessed alongside groundwater recharge and groundwater discharge capacity. This will help to determine if salinity problems are likely to develop in the landscape
  • current agricultural practices should be reassessed to improve their water-use efficiency.

Biodiversity values of brigalow vegetation

  • it is likely to take around 90 years before regrowth brigalow recovers 90 per cent of the floristic and structural characteristics of mature brigalow vegetation
  • management practices such as tree thinning and allowing for the accumulation of logs and litter will promote woody species diversity and help to increase structural variability
  • regrowth vegetation has significant biodiversity value, despite its immature stature. It provides habitat for flora and fauna and is critical for increasing native vegetation coverage in cleared landscapes.

Conclusion

Native vegetation planning and management should consider the needs and values of landholders, property or catchment size, and the position of important landscape features (salinity recharge/discharge areas, other areas of brigalow habitat).

Optimal outcomes are likely to be achieved by retaining a mixture of regrowth and mature brigalow vegetation in the landscape.

This will provide a range of habitats for plants and animals, assist with minimising salinity risk, and help to lessen adverse impacts on agriculture.

Read more about Sustainable agricultural landscapes.