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Some Trees can be Weeds

Robina pseudoacacia, a highly regarded timber durable
species from the USA, choking a stream on a farm in southern NSW.

When searching for new and profitable timber species there is a risk that farmers may introduce or encourage the spread of serious weeds. Many introduced commercial tree species are themselves weeds. For example, pines are able to invade native forest due to their tolerance of shade and tagasaste, a promising fodder tree, is a serious weed of native forests on sandy soils in Victoria. Amongst the alternative timber species many have become serious 'urban' weeds, having escaped from ornamental plantings.

Farmers need to be aware of the risks of introducing new species to an area that might be further spread by stock, birds, wind, water or other means. Once established the cost of control can be very much more than the contribution these trees might make to the farm. Introducing new genetic material of native species can also irreversibly change the genetic composition of existing vegetation in the area. This can happen through hybridisation or interbreeding and can be very difficult to reverse in the future.

There are a number of web sites that can be used to assess the weed risk of particular species:

The Global compendium of weeds is a useful start when researching exotic species.

Within Australia the Australian Quarantine Inspection Service (AQIS) provides an Import Conditions Database which lists the import conditions of various commodities and advises whether you require a permit, inspection, mandatory treatment or minimal entry requirements to import your species.

The Department of Agriculture in Western Australia provides comprehensive information on the weed characteristics of many species.

As an example, we recently received a request for information on African Blackwood Dalbergia melanoxylon (ebony). Dalbergia melanoxylon produces one of the finest timbers in the world, with round logs of this species fetching up to US$18,000/m3. This timber is used in Australia in musical instruments and as is used as inlays in fine furniture.

Our research found that this species had been imported to Australia as a promising timber species and planted in a trial in Western Australia. However, it was soon discovered that the species is a very aggressive weed and was quickly eradicated from the trial. Knowledge of the extreme weediness of this timber was not widespread. Despite the potential value of the timber, this was an important reminder of the risks of introducing new species into the country or into a new area.

Please be careful when introducing new species to your farm. Watch for initial signs of weediness and eradicate any species that is likely to get out of control.

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