Timber trials: Mallee native tree lNindbreaks to ease erosion, add shelter by Robin Taylor

IN A season where severe dust storms have swept through the Victorian Mallee, farmers are looking at shelterbelts as a way to reduce this wind erosion.

But while many farmers are enthusiastic about revegetating their properties and recognise the multiple benefits that trees can bring, choosing the right species is not always easy, especially for landholders in low-rainfall areas such as the Mallee.

According to Greening Australia's Ron Dodds, much research has been carried out on forest species for higher-rainfall zones, but less is known about how various species will perform in lowrainfall areas.

A joint project by the Birchip Cropping Group and Greening Australia is seeking to redress the balance by evaluating four native species for their dryland timber potential in the Mallee. The results so far are very encouraging.

As well as comparing species, the trial will assess the benefits of shelterbelts in productive farming systems, particularly on highly erodible land types.

Comparing belt to block design

In August 2001, a farm forestry block and a 1.7 km alley-farming shelterbelt were established 30 km north of Birchip in the southern Mallee, to compare the performance of different tree species in both belt and block situations.

The four main species used in the trial were:

  • sugar gum (Eucalyptus cladocalyx)- three provenances
  • flat-topped yate (Eucalyptus occidentalis) - two provenances
  • river red gum (Eucalyptus camaldulensis)- two provenances
  • red ironbark (Eucalyptus tricarpa) - one provenance

These species were chosen because of their potential widespread application for farm forestry in lowrainfall areas throughout Australia, their ability to grow rapidly to a height of more than 10 metres, and their durability and potential as premium appearance-grade timbers.

The shelterbelts are 14 metres wide and comprise two inner rows of planted timber species and two outer rows of local native shrub species, direct-seeded.
Species Treatments
Treatments number Species/Provenance Eucalyptus cladocalyx = sugar gum, Eucalyptus OCCidentaits = flat-topped yate, Eucalyptus camaldulensls = river red gum. Eucalyptus tricarpa = red ironbark Mean height(cm) Belt Mean height(cm) Block % survival Belt % survival Block Mean Health score belt Mean Health score block
1 Eucalyptus cladocalyx Wail 50.6 29.1 62.5 70.7 4.67 2.5
2 Eucalyptus cladocalyx Wirrabarra 60 31.3 87.5 33.3 4.95 2.24
3 E. occidentalis SPA Bundalee (20444) 81.4 79.7 93.3 54.7 5.16 4.24
4 E. occidentalis Truslove (15416) 93.2 82.1 84.4 61.3 5.16 4.39
5 E. camafdufensis Lake Albacutya (19708) 120.5 75.2 93.75 77.3 4.6 4.57
6 E. camaldufensis Silverton (19868) 82   100   5.18  
7 E. tricarpa Bendigo (15201) 88.1 77.1 100 78.7 5.16 4.35
8 E.cladacafyx (Yanda) 55.1 26.3 85.94 50.7 4.97 2.11

In August 2002, the trial was measured for growth rates, percentage survival and tree health. The results are very impressive, says Mr Dodds.

"Survival and growth rates of the forestry species are phenomenal considering that the region had experienced the five driest years on record before the trees were planted."

The direct seeding results were also excellent, helped by good late spring rains in November after planting. Of the four 'best-bet' timber species, swamp yate, red gum and red ironbark stood out, while sugar gums were struggling.

Comparison between the timber belts and the block showed that all species performed considerably better in the belts in terms of height growth, health scores and survival.

Advantages of tree belt design

According to Mr Dodds, there are several reasons for the differences, including a localised rabbit warren near the timber block, high levels of wind erosion and sandblasting, and higher numbers of weeds, due to reduced spraying to try to maintain cover to prevent erosion.

"Over time I would expect that belts would outperform blocks because of a permanent edge effect, where belts of trees can exploit the water not used by the annual crops and pastures growing nearby," he explains.

Since the measurements in August, Dodds says the trees have continued to do surprisingly well, considering the lack of rainfall.

"Trees in the block are recovering and some of them appear to have overcome their earlier setbacks and might have growth rates comparable to the belt trial."

Envirofund trials

As a result of the success of this trial, the Birchip Cropping Group has secured funding under the Federal Government's Envirofund for another two trials. New sites will be established to add further to the information collected on the effects of shelterbelts in productive farming systems.

BCG manager, Alexandra Gartmann, says the next phase of the trial will focus on monitoring the effect of the shelterbelts on wind levels and crop production.

Over the next few years the group will measure parameters such as crop yield responses, wind speed and a range of other measurements to determine the effects of the shelterbelts.

It is possible that the shelterbelts could be selectively harvested and coppiced. Dodds is convinced of the benefits, after planting shelterbelts on his own property on a light sandy soil, north of Nhill in the Victorian Wimmera, six years ago. He says they are definitely having a beneficial effect on reducing wind speed.

Birchip Belt/Block survival comparisonBirchip Belt/Block height comparison (cm)

For more information abont the Birchip project, inclnding specific paddock layont and the project species mix, contact the Birchip Cropping Group 03 5492 2787; email bcg@rnralnet.net.au; or Mr Ron Dodds, Greening Anstralia Victoria 03 5381 1010; email rondodds@netconnect.com.au