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The GREEN HORSE - sustainable horsekeeping

FEBRUARY MARCH 2008
Vol 29-5

In the February March 2008 issue of The Green Horse you will find the following articles:

Information Exchange - Reader’s Tips, Views and Questions
Tree Exclosures by Chris Hall
Weed Watch - Cootamundra Wattle by Nicola Field
Seed Collection Pt 2
Growing Equine Herbs - Lemon Verbena by Fiona Adams
National Parks Trail Partnership
Deeds, Steeds and Weeds
Getting It Right - The Property Hunt by Chris and Tracey Ferreira

TREE EXCLOSURES
by Chris Hall

This tree exclosure has been built to protect the very old red-gum from damage by horses, however it could be improved by planting an understorey of plants within the exclosure fence.

Tree exclosures provide a model for managing lone paddock gums on small and large properties. Many paddock trees, especially native gums, are under tremendous stress from several different factors, including dieback, stock presence, cropping, salinity, changing water tables and diseases such as Phytophthera and Mundulla Yellows.

The idea of managing the ground beneath isolated paddock gums differently has evolved in response to the plight of our dying heritage, and the concept of a tree exclosure was born. A tree exclosure exists when stresses such as stock, cropping, fertilisers and pesticides are removed from beneath a tree’s canopy, and the area is rested. At the same time the area is planted thickly with mainly nitrogen-fixing native understorey plants. Planting understorey species such as wattles and she-oaks does two important things: they put nitrogen back into the soil, and they encourage native birdlife to return and clean the leaves of harmful insects.

We are in effect ‘resting’ the patient, in this case the gum tree, by allowing the excess nutrients in the soil around the gum to leach out of the tree’s root zone. This nutrient overload may come from decades of stock presence, as well as from chemicals and fertilisers. The combined effect of resting the soil, removing as many chronic stresses as possible, plus replanting the understorey, will hopefully enable stressed gums to rejuvenate themselves and put on new growth.

The presence of an understorey encourages helpful native birds to return, keeping trees healthy. Honeyeaters and pardalotes in particular vacuum the leaves of sap-sucking insects such as lerps. Their beaks are designed to clip lerp scales off leaves. Given the likelihood that lerps also pass on the tree disease Mundulla Yellows when they inject into a leaf, just as a mosquito does to us, the importance of encouraging natural controls for lerps, such as honeyeaters, becomes starkly apparent.

Another benefit of a tree exclosure is that natural regeneration will occur probably within the first year, with young self-sown seedlings popping up near the parent tree.

nother encouraging sign of an exclosure’s success would be the emergence of new leaf growth, leading to greater canopy cover. The ageing gums in the exclosures at Lindsay Park Thoroughbred Stud at Angaston in South Australia have put on new leaf growth in their second year after being exclosed. In the two previous years there was no new growth at all.

Design and management
1. Select either an isolated paddock gum, or better still, a group of gums which could all be exclosed together, thus saving fencing costs. The exclosure only needs to be fenced if stock such as horses are present or if kangaroo damage is likely. Remember to include a gate for maintenance purposes and to allow cleanup grazing after four or five years. Cleanup or ‘crash’ grazing means allowing horses or other stock in for a very short period of 2 to 3 days a year to nibble.

2. Try to extend the enclosed area well beyond the vertical drip-line of the tree’s outermost branches.

3. Plant tubestock randomly throughout the exclosure in winter months but with she-oaks tending to be out beyond the drip-line of the tree.

4. Maintain the area by slashing/mowing, being careful to look out for self-sown gum seedlings.

Plant Suggestions Depending on the local soil types and conditions in your area, plants such as various wattle species or christmas bush are suggested for under the tree canopy; beyond the tree’s dripline - drooping she-oak or swamp wattle, and old man’s beard, kangaroo and wallaby grass, bluebush or ruby saltbush amongst all these could be used.

For further information on species suited to your area contact your local Landcare Office or Landcare Australia online www.landcareonline.com, or try www.greeningaustralia.org.au, or for books on native trees, CSIRO Publishing - www.publish.csiro.au or Native Growth Holdings online nursery, books and ordering system www.nativegrowth.com.au.

Article courtesy Land Management Program South Australia.