Natural areas are vital to the biodiversity of Australia’s unique flora and fauna and to its unique cultural identity. With the onset of climate change protection of these values has become even more important. With the loss of habitat from wildfires, tree clearing and drought, even small patches of bushland are valuable habitat for species of plants and animals. But throughout Australia, small patches of bushland are under continual and often severe threat from introduced species not native to the area.
The most common weeds found in bushland are known as environmental weeds. These weeds are usually spread from urban gardens close to parks and reserves via bird droppings, water and wind.
The concept of environmental weeds was not recognised until the 1970s. It took some years for authorities to recognise the danger of environmental weeds. Most government research and suppression was orientated to weeds of agriculture, so environmental weeds had many decades to smother vegetation e.g. Hedera helix (English Ivy) or to establish widely spread populations.
Most bush regenerators regard the benchmark condition as the vegetation as it existed prior to European colonisation. So species such as Pittosporum undulatum (Sweet Pittosporum) native to coastal New South Wales and eastern Victoria are regarded as environmental weeds in the ranges around Melbourne. Acacia baileyana (Cootamundra Wattle), indigenous to a small area of southern inland New South Wales is now self-propagating in widespread localities around eastern Australia.
In 1967 a couple of sisters in New South Wales – Eileen and Joan Bradley – wrote a small publication named Weeds and Their Control. They had found that by clearing weeds from areas of good bushland, the indigenous plants were able to regenerate and out-compete the weeds. In 1988, Joan Bradley produced a larger publication named Bringing Back the Bush – The Bradley method of bush regeneration. The Bradleys preferred not to use any poison, but to physically remove the whole plant, that way insuring the plant would not re-grow.
In Victoria the modern era of bush regeneration was launched at a seminar sponsored by the City of Nunawading in 1980, organised by the late John Brandenberg. Pioneering fieldwork commenced in the Organ Pipes National Park (initiated by the Friends of the Organ Pipes in 1972) and in Sherbrooke Forest (initiated by the Friends of Sherbrooke Forest).
Some weeds require specialised control techniques. For example in some situations such as Wet Forest, the lower branches of Ilex aquifolium (Holly) layer and produce small trees surrounding the parent tree. It was found that just poisoning the parent tree would not kill the layered branches, so these branches had to be physically removed or poisoned separately. This also applies to any plant that produces layers.
The Bradley technique of physical removal is not practical for large trees. Evelyn Hickey from Save the Bush, a National Trust (NSW) innovation, developed the ‘drill and fill’ method for poisoning large trees and this is the preferred method used today. Full-strength glyphosate is used as the preferred poison.
Trees such Sweet Pittosporum require the poison to be evenly spread around the trunk, preferably close to the ground to kill the whole tree. Using the drill and fill method works better than frilling. Friends groups eventually obtained funding from government grants to purchase battery powered drills.
Plants in the Asteraceae family (Daisy) produce millions of wind carried seed, so should be controlled before they flower. Trees in the Aceaceae family (Maples) have winged seeds that can be carried some distance by the prevailing winds.
One of the most important activities in weed control is follow-up. Weeds that produce a viable berry can have seed stored in the soil for many years, so if not followed up will result in the area being colonised by weedy species once again. It is more rewarding for volunteers to make small achievements in bush restoration than to tackle areas too large to allow regular follow-up.
Friends groups have played a significant role in the control of these weeds. Friends groups had to learn by trial and error. They not only had to learn to recognise a weed, but had to learn how to differentiate them from the indigenous vegetation that grew in their park or reserve. Before commencing removal of environmental weeds a thorough botanical survey of the area must be carried out.
Today hundreds of volunteers working on bush restoration throughout Australia. It takes only a few individuals who are enthusiastic about a particular park or reserve to form a Friends group. Groups must obtain the permission of the authority in charge of managing the area.
Muyt, Adam 2001. Bush Invaders of South-East Australia.
Blood, Kate 2001. Environmental Weeds – A Field Guide for SE Australia. CRC Weed Management Systems.
Bradley, Joan. 1988. Bringing Back the Bush – The Bradley Method of Bush Regeneration.