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.

Pioneering work

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).

Special techniques

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

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.

Further reading

Freshwater, Vivien and Diane Ward. 1993. How to Restore and Manage Bushland on an Urban Block. Leaflet.

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.

Friends of Sherbrooke Forest and Dept. of Conservation, Forests and Lands. 1989. Weeds of Forests, Roadsides and Gardens (15MB).

Editor’s note:

Gardeners can find information about this impressive tree in numerous books and websites. But we have decided to publish this short paper because it is a personal perspective from an eminent parks person. The paper dates from about the late 1990s.

 

The genus Bauhinia embraces a family of remarkably diverse trees, shrubs and climbers found in tropical or sub-tropical climates both north and south of the equator.

With their orchid-like flowers and curious ‘camel’s foot’ leaves, most tend to be a source of curiosity rather than strong landscape features. However two of the tree species do form features in their own right and are much valued by plantsmen. There are Bauhinia purpurea and Bauhinia blakeana.

Bauhinia purpurea, which is found naturally in India, Burma, Vietnam and South China, has both the largest flowers and largest leaves in the family. Its intense purple flowers are the subject of much admiration though the tree itself tends to be untidy in shape and therefore of limited landscape value.

Bauhinia blakeana, ‘The Hong Kong Orchid Tree’, though listed as a separate species, is of mysterious origin. The first tree was discovered near the ruins of a house on the seashore of Hong Kong Island in 1908 by the Fathers of the French Mission at Pok Fu Lam. It was named after Sir Henry Blake, Governor of Hong Kong from 1898 to 1903, who was also a keen botanist. By coincidence the current IFPRA President-Elect lives on the site of the original tree.

Though believed, initially, to be a mutation of B. purpurea, B. blakeana possesses a number of distinctive characteristics in both flower and leaf form which give doubt to this theory. Though fast growing, B. blakeana rarely exceeds 6 m. in height and is characterised by a twisted stem and long, spreading, drooping branches on which can be seen a profusion of orchid-like flowers. These flowers consist of 5 spreading and unequal petals in colours varying from carmine red to burgundy-but a deep pink hue is dominant. The fifth petal of each flower is striped purple, this emphasising the orchid-like appearance.

B. blakeana is sterile, the flowers never maturing into fruit or seed. Propagation is by top grafting on to rootstock of B. purpurea.

When in flower B. blakeana is unequalled in the genus; and is therefore much valued for its ornamental qualities though its brittle branches suffer from storm damage. Today the progeny of the lone tree in Pok Fu Lam can be found ‘en masse’ throughout South China, also in Queensland, Australia and elsewhere.

B. blakeana was formally adopted as the floral emblem of Hong Kong in 1965 and features in both the government’s and Urban Council’s Coat-of-Arms. A stylised version also constitutes the logo of the Urban Council and has even been copied by a major city in the United Kingdom! When Hong Kong reverts to China in 1997 the Bauhinia will again form the emblem of the territory. This time it will symbolise the new Special Administrative Region with a small star located on each lobe of the distinctive magenta flower. Rarely has a solitary tree received more prominence in such a short time and from such humble beginnings!

 

R.F. POLLARD (Roger)

President-elect, IFPRA (International Federation of Park and Recreation Associations)