Land and Water Link

Issue No. 12, May 2002

Trees to Combat Salinity A comprehensive new guide to using farm forestry to combat salinity is set to improve tree-planting outcomes. Dryland salinity is one of Australia's biggest, long-term land degradation problems. Yet it has only entered the collective consciousness of Australians

in the past ten years. The realisation that tree clearing contributes to dryland salinity has fueled an ongoing debate about how many trees, if any, should be replanted in an attempt to halt the problem. For those who look to tree planting as a solution, the critical questions have been how many trees, and where to plant them. To shed light on these complex issues, hydrologists, plant physiologists and foresters from CSIRO and other agencies, joined forces under the Joint Venture Agroforestry Program. The result is a landmark publication: Trees, water and salt: An Australian guide to using trees for healthy catchments and productive farms. Launched in March this year, the book describes hydrology concepts and practical tree planting options to reduce salinity at the catchment scale. Advice is offered on how to locate trees in the most effective place for salinity control and at the same time, achieve the best growth. Five scenarios are discussed. These involve tree planting:

• in high recharge areas such as sandy or shallow soils
• in blocks for wood production in rotation with agriculture
• in belts on hillslopes
• in belts mixed in with agriculture
• over shallow, saline watertables.

According to CSIRO Land and Water researcher Dr Richard Stirzaker (co-editor), 'We describe the theory behind each option to help people decide for themselves what part of the catchment and in what arrangement – alleys, belts or blocks – to plant trees as part of a broader strategy. And we discuss the chances of success for each option in different catchment situations.' Reflecting on the salinity debate, Dr Stirzaker says 'Many of the early warnings and initial predictions about the extent of looming salinity problems came from the hydrologists – those tracking the amounts and fate of water. They rightly said we weren't doing enough to fix the problem and tried to predict the area of agricultural land that we would need to plant with trees to halt salinity. Popular opinion in the early 1990s put it at 10%, and to many that seemed achievable. 'But by 1997, hydrologists were talking about the need to plant 70% to trees in many catchments. This would mean a total change in the way the land was used and it would take decades to know if the tree plantings worked. Hence, many began to question whether trees could provide an answer.' Dr Stirzaker adds, 'The debate continues to be vigorous and proposed alternatives to tree planting, such as engineering solutions, are also yet to be proved. However, as we become more adept at identifying those catchments where we should focus our efforts, Trees water and salt offers a practical guide to the most effective tree-planting strategies.' Trees, water and salt links the knowledge and long-term predictions of the hydrologists with the knowledge and needs of farmers. 'These are two very different disciplines and two very different ways of thinking. I'm proud of the fact that this book looks at the catchment reality – the cumulative and long-term effects of what we do, alongside the paddock-scale necessity – the need for annual productivity and returns', says Dr Stirzaker. 'If trees are part of the solution to salinity, and I think they are, then this book will be of value to farmers, extension officers and catchment management authorities.' Trees, water and salt: An Australian guide to using trees for healthy catchments and productive farms edited by R. Stirzaker, R. Vertessy and A. Sarre, (RIRDC Publication No 01/086) is available from RIRDC, either as a full print version or as a summary online.

For further information:

Contact

Dr Richard Stirzaker
Phone: 02 6246 5570