Break of Slope Plantations

Note Number: AG0385
Prepared: May, 1996

The "break of slope" is that part of the landscape where the ground surface begins to flatten out from the steeper slope of the hills (see Figure 1). Research suggests that in some areas of the Goulburn Broken catchment, plantations along the break of slope can intercept groundwater recharge and thus reduce groundwater pressure in lower areas. With careful selection of tree species and appropriate follow up management, such plantations also have the potential to produce high quality timbers and generate additional income for the landholder.

Figure 1. This cross sectional diagram of the Warrenbayne Hills shows the correct position for the break of slope plantation

Why plant on the break of slope?

The diagram shows the correct position to establish a break of slope plantation. Rain falling on the rocky hill top recharges the groundwater system. This groundwater is unable to penetrate the unfractured bedrock and moves slowly down the slope, dissolving salts from the soil. At the base of the slope the groundwater is forced to the surface, where salt is concentrated by evaporation. This is your typical groundwater discharge area or "salt patch",within which groundwater salinities can reach 18-20,000 EC. Critical to the importance of break of slope plantations in salinity control and agroforestry are the following factors.

At the break of slope, groundwater is relatively close to the surface and fresh. Research in Western Australia has shown that trees can access and use considerable quantities of this water. In doing this, the plantation is able to reduce both groundwater pressure and flows into the saline discharge areas.

Soils at the break of slope are generally deep and well drained - ideal for commercial forestry. Further up the slope soils become too shallow, while further down the slope, the groundwater maybe either too deep or too salty for good tree growth.

Suitability of break of slope plantationsfor salinity control

The use of break of slope plantations in salinity control is limited by the suitability of the underlying bedrock. Many areas of the Goulburn-Broken catchment have highly fractured bedrock systems. In such areas, groundwater percolates down through this fractured and weathered bedrock and is unavailable to trees at the break of slope. In such areas break of slope plantations will not be an effective salinity control option.

Break of slope plantations will be an effective salinity control option in areas where the bedrock is not fractured, such as the hills between Euroa and Swanpool.

Members of the Warrenbayne-Boho Land Protection Group are presently involved in a project aimed at quantifying the salinity and agroforestry potential of break of slope plantations. Seven plantations have been established and group members are working with staff from the Centre for Land Protection Research to monitor tree water use and changes in groundwater levels.

Further advice and assistance

Landholders from areas in which break of slope plantations offer an effective salinity control option are eligible for financial assistance through the Salinity Program to help meet the capital cost of establishing the plantations.

For further details on break of slope plantations and financial assistance available contact your local office of Department of Primary Industries.

(Reprinted from Goulburn Dryland Salinity Program's Resource Kit)

Contacts

Australian Forest Growers (AFG)PO Box E18Kingston ACT 2604Ph. 02 6285 3833Email: afgnat@safetyweb.com.au

Further information

NREs Private Forestry Web site:http://www.DPI.vic.gov.au/forestry/private.htmDPI Customer Service CentrePh. 136 186

Acknowledgments

This Information Note was prepared by Denise Fontana, Benalla