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Alien Invaders: Learning about Biodiversity by Monitoring Environmental Weeds

Contributed by Gary Shadforth, Royal Botanic Gardens Melbourne, South Yarra, Victoria, Australia

Alien History

The Royal Botanic Gardens Melbourne has a long history of interest in, and scientific study of, plant biodiversity. Currently this may involve conservation botanists studying the nature of natural ecosystems and particular plant species that occupy them. Over 150 years ago biological diversity was respected in a different way. The Director and first botanist of the Botanic Gardens, Baron Ferdinand von Mueller, was a highly accomplished naturalist and botanist and had a great interest in the variety of plants in Australia. He was also very active in the local acclimatization societies. These societies were involved in the introduction to Australia of a variety of exotic plants and animals to remind people of their European heritage. Apparently the natural environments in Victoria were too wild, untidy and alien. According to contemporary botanists such as von Mueller, this extra variety from Europe was a good thing. He is said to have carried a knapsack of blackberry cuttings on his field trips through the countryside and he progressively planted them along the way. Such a useful plant, he reasoned, would be valuable for travellers through the bush.

This is from somebody who had a great appreciation of the Australian bush. Von Mueller was very interested in the practical uses of plants; he helped create industries for eucalyptus oil and recommended the introduction of exotic conifers for their value as timber. This laissez-faire approach to diversity went both ways: he was also keen to advocate the value of Australian plants in other parts of the world. His advocacy has resulted in Australian plants such as eucalyptus being a significant environmental weed in other countries. Yet von Mueller had a great appreciation of the Australian bush and lamented its destruction.

Baron von Mueller was a contemporary of Charles Darwin, but he resisted Darwin's ideas of natural selection and transmutation of species. The prevailing understanding for most people was that species did not change and existed forever. The study of ecology is more of a twentieth century phenomenon and takes into account the notion that things do change. People now acknowledge that different species of plants, animals, fungi and micro-organisms have an effect on each other. This may be positive, as a food source or in a symbiotic relationship, or negative, in such cases as disease, competition or predation.

Over thousands and millions of years these impacts have altered the nature of species in the ecosystems involved. Plants may develop a chemical resistance to insect predators. Flowers may become more attractive to a certain pollinating bird. Insects may overcome the chemical disincentives that plants produce to keep from being eaten. A natural ecosystem is a very complex and intricate web where there is a tug of war on each strand. Each ‘tug’ from one species is responded to by a range of other species. This results in continual evolutionary change and often a very delicate balance. A sudden drastic change that affects a few species, such as the introduction of a weed, will have ramifications on a great range of other species.

Ecosystems and the species they contain have been evolving on the Australian landmass for millions of years. Much of the flora of Australia still shows relationships to species that lived when the Continent was part of the southern supercontinent of Gondwana over fifty million years ago. While these species have managed to remain stable by existing in habitats that they adapted to all that time ago, climatic conditions have altered and newer species have arisen that have adapted to the newer regimes. Along the way species have responded by adapting to each other's presence, so that whole new floras have arisen in isolation from other continents. Isolation such as this generally leads to a high number of endemic species, species that exist nowhere else on earth. This is common on islands that are not easily accessible by animals or plant material: New Zealand and New Caledonia are such examples. While their floras show Gondwanan relationships with the other southern continents, they separated from the supercontinent even earlier than Australia. In isolation their floras then evolved to become quite distinct from any other.

Alien Traditions and Biodiversity

I have frequently noted that visitors to the Royal Botanic Gardens Melbourne refer to all the English plants there. Unthinkingly, a number of people have an idea that most plants here are either Australian native or they are from England. Perhaps this is an old-fashioned notion of the traditional English garden with its lush collection of colourful, floristic shrubs, perennials and annuals. On further reflection, especially if they read the labels, people realise that these plants come from many parts of the world. In the eighteenth and nineteenth centuries the combinations of the English interest in exploration, botany and landscape lead to a form of English garden. The English tradition in this sense, like von Mueller, is to see plants as collectibles, isolated from the environment they have adapted to over millions of years.

Britain is in fact an island with low species diversity and few endemic species. Even though as an island it has been somewhat isolated from the European continent, most of it was covered in ice as recently as eighteen thousand years ago at the end of the last Ice Age. When the ice retreated and provided new opportunities for plants and animals, it was mostly opportunistic species that took advantage. These species included plants that are quick to colonise new patches of land and remain competitive with other plants that come along – the sort of plants that might be considered `weedy'. Most of the flora of Britain is made up of these recent arrivals from continental Europe, as well as many others that have arrived even more recently from other parts of the world. Eighteen thousand years is not a long time for new species and ecosystems to develop.

When Europeans first reached Australia it was either with great fascination at the botanical novelty and variation or with contempt for its alien newness. Australia has an enormous wealth of biological history, diversity and endemism. However, since European colonisation, it seems that many Australians have retained the old European cultural inheritance that sees this flora as a collection of plants that will always be around. Many of the introduced weeds that now threaten our indigenous flora are plants that have been much loved in the Old Country: English ivy, Scotch thistle, holly, English broom and of course blackberry. The love of plant collecting has also introduced more serious concerns from places with climates and conditions similar to our own, such as South Africa, the Mediterranean, South America, California, Mexico, India and even other parts of Australia. Pittosporum undulatum is a garden escapee that is indigenous to East Gippsland (Victoria).

These sudden arrivals, without the original restraints that may have evolved with them such as predators, pathogens or competitors, may find they have a clear run in a new ecosystem. Such an ecosystem contains species that, over their millions of years of balanced tug of war, never had the opportunity to develop the means to contend with such a newcomer. These environmental weeds will limit the opportunities for indigenous species for space, light, water, nutrients and access for pollination, seed dispersal and germination. They can even change the entire nature of microclimates or fire regimes. Some weed species have the capacity to completely blanket areas of natural vegetation. While indigenous Australian people have an intimate relationship with natural habitats, non-indigenous ones have only fairly recently come to acknowledge the great natural inheritance that they have. General interest in Australian flora only became evident from about the 1960s, when Australian native gardens were becoming popular. Nowadays communities understand the significance of their local indigenous flora. Local councils commonly use indigenous plants to planting along streets and in reserves, while indigenous plant community groups are proliferating.

While weeds have always been considered a problem in agriculture and horticulture, they have been somewhat taken for granted in the natural environment. Governments have responded with such initiatives as the National Weeds Strategy (1997) and the Victorian Weeds Strategy (1998). An estimate prior to 1998 put the direct cost of weeds to Victorian agriculture at more than $360 million per year. Even when their dangerous presence has been noted, very limited scientific monitoring has been done. Monitoring is important for producing management strategies to control specific weed species, particularly when budgetary considerations are an issue. Nowadays the devastation that weeds are having on Australia's biodiversity is being taken seriously. Part of this seriousness must be in communicating it to young Australians – to increase understanding, raise awareness and develop action strategies to manage this increasing environmental issue.

What is a Weed?

So far I have used the word ‘weed’ loosely. There are many things people might consider weeds to be. Weeds may be regarded as plants that:

  • can colonise quickly and aggressively
  • occur in our gardens without being put there
  • are harmful to livestock
  • are poisonous to people
  • are aesthetically unattractive
  • compete with food crops for growth
  • are excessively aggressive and competitive in the garden
  • grow naturally
  • are introduced or escape, and have naturalised into natural ecosystems.

A weed does not necessarily conform to all of these categories. Children (and many adults) are often likely to believe that a weed is a certain taxonomic category of plant or that all plants that are not carefully cultivated in a garden or a farm are weeds. A weed can simply be regarded as a plant out of place.

Our emphasis is on environmental weeds, those alien plants that have naturalised into natural ecosystems. One quarter of these plant species started life as garden plants, attractive ornamentals to improve our environment. As the nursery industry is continually on the look out for new, interesting and hardy horticultural specimens, the list of escapees increases. Many environmental weeds are still sold commercially as useful, hardy plants that are difficult to kill - and look very nice.

The Royal Botanic Gardens Melbourne, as part of its long established role in the study of plants, their diversity and the ecosystems they belong to, particularly in Australia, is active in studying and communicating these threats.

The Project

The Royal Botanic Gardens Melbourne has a stated mission:

`To advance the knowledge, enjoyment and conservation of plants through excellence in biodiversity research and management, horticultural displays and educational programs'.

Conforming to this mission, the Royal Botanic Gardens has involved itself in a `Science Partnership' project with the Victorian Department of Education, Employment and Training. Our particular project is titled 'Alien Invaders: Identifying and Monitoring Weeds in the Environment'. Science Partnership projects are a means of linking school students and their teachers with the work of professional scientists. The project invites schools to participate in surveying local areas of natural vegetation for specific species of weeds. Students involved range from year 7 to year 11 and their schools tend to have an active environmental programme in their curriculum.

The project was initiated in October 2001 to coincide with `Weedbusters Week' when students from nine participating schools visited the National Herbarium of Victoria at the Royal Botanic Gardens Melbourne for an official induction. Our scientific staff described their work and emphasised its value and threats to our local biodiversity. Students were shown what the project entailed and the benefits that it would have. Another nine schools joined in this year. The staff of the National Herbarium of Victoria work on the systematics, taxonomy and conservation of Australian flora and fungi. Together with scientific staff at the Australian Research Centre for Urban Ecology (ARCUE) and Royal Botanic Gardens Cranbourne, there is a wealth of scientific expertise that students can be exposed to.

ARCUE is a division of the Royal Botanic Gardens that was created in 1998 to research the diversity of natural ecosystems in urban environments and to work to conserving and advancing the knowledge of it. Its stated vision is:

To foster the survival of viable natural ecosystems and the preservation biodiversity in urban areas, and to help minimise future human impacts on the natural environment due to the urbanisation of the Australian landscape.

The students focus on looking at natural environments in an urban area. These environments are likely to be disturbed by the impacts of urbanisation, including the presence of a significant suite of weeds. While the presence of weeds is now a well-known threat, the precise distributions of weed species is not so clearly known and documented. Involving students in such a scientific investigation improves our knowledge, while being a very practical tool in allowing students to learn about ecology and biodiversity. As the project evolves it is hoped that any interested school will participate.

Students are introduced to about 60 species of weeds. They are a selection of easy to identify and significant plants and will include a range of forms, habits and preferences. They include tree weed species such as Sweet Pittosporum (Pittosporum undulatum) which is a native of East Gippsland and is commonly found sprouting in forests in the eastern suburbs; or the herbaceous Paterson's Curse (Echium plantagineum) which can be seen blanketing areas of the northern suburbs. Each of the areas represented by the schools will contain a number of these selected species.

To help their monitoring in the field, schools are given booklets that contain information about each weed species, including spotting characteristics, photographs, line drawings, descriptions, distribution maps and identification keys. This information comes mainly from the four volumes of Flora of Victoria, produced by the Royal Botanic Gardens Melbourne. They will also receive monitoring manuals that will include instructions on surveying, collecting and identifying plants and sheets for recording and reporting. Scientific and education staff will develop a procedure for recording and monitor populations of environmental weeds that is appropriate to upper secondary school students.

Students can enter their data directly into a RBG database through the Internet. Feedback on their data, including that of significant collections such as new weeds and range extensions, is made available via the Internet. Schools are also provided with kits that will allow students to press and mount their own herbarium collection of weed species. These kits will include a plant press with cardboard and instructions for proper preparation and mounting of the specimens. Selected specimens (especially of new or significant records) may be lodged at the National Herbarium of Victoria to become part of a significant national botanical collection. To supplement these scientific activities, teachers are provided with educational resources generated by the RBG Education Service that will help them communicate the concepts of biodiversity, conservation and environmental threats such as weeds.

Principles of Environmental Education

This project can be viewed as a multidisciplinary activity can cover all subject areas of the school curriculum. It generates an awareness of the natural environments close to where students live and of the impacts that people are having on them. This leads to a wider awareness of national and global issues. There are obviously questions that may be raised and debated in the course of the project. For example, why should a rather dull indigenous grass be better that a very colourful introduced plant that grows profusely on riverbanks? The underlying values that we want to instil include respect for and understanding of the natural diversity and an appreciation of the interdependence of species and how they can be destroyed by human impacts for short-term interests.

The content of the project covers not only what the local environment consists of, but also how ecosystems work and what their interrelationships are. This leads to an appreciation of how they may be affected by outside impacts. Students will learn and develop skills that are used by scientists in the field to monitor threats to ecosystems in order to make assessments on what damage has been done and what the potential dangers are. With this awareness, values, knowledge and skills, young people will be equipped to make decisions and take actions. This work will make an important contribution to the preservation of our natural and global inheritance, ensuring it is treated respectfully now and into the future.

From the teacher’s perspective, concentrating on what initially seems like an unappealing topic in weeds (hence the Alien Invaders package), is a very neat way of allowing students to learn in a very hands- on and practical manner. While weeds as a threat are the project’s focus, students can also become familiar with the indigenous vegetation of their own environments. The weeds receive rough hands- on treatment, while the indigenous flora can be observed more respectfully. It is important that they can personally identify with the value of the project and see their input as an important contribution.

Surveying and studying the impact of weeds is an approach that any teacher can take with their class in teaching about ecology and the environment. While becoming familiar with local ecosystems, students can do something practical and valuable and also learn about some of the intricacies of interspecies relationships and the complex dynamics of sudden changes in an ecosystem. This is all with the classic ‘good guy - bad guy’ theme. We look forward to a happy ending.


Victorian Weed Strategy (1998). Melbourne: Department of Natural Resources and Environment, Government of Victoria
The National Weeds Strategy: a strategic approach to weed problems of national .significance (1997). Canberra: Agricultural and Resource Management Council of Australia and New Zealand, Australian and New Zealand Environment and Conservation Council and Forestry Ministers, Commonwealth of Australia.
Carr, G.W., Yugovic, J.V. and Robinson K.E. (1992). Environmental Weed Invasions in Victoria. Department of Conservation and Environment, Melbourne, Australia.
Adair, R.J. and Groves, R.H. (1998). Impact of Environmental Weeds on Biodiversity: A Review and Development of a Methodology. The Director of the National Parks and Wildlife, Biodiversity Group, Environment Australia. Canberra, Australia.
Foreman D.B., Walsh N.G. and Entwistle T.J. (1993). Flora of Victoria Volumes 1–4. Royal Botanic Gardens Melbourne, National Herbarium of Victoria. Inkata Press.