Hand removing weeds from rehabilitation areas on a Pilbara mine site, tough work!
For the best part of the last fifteen years I've been involved in the management of invasive weeds, from years of on ground control lugging a solo spray pack around through to designing adaptive management plans, strategies and monitoring programs. Most of this time has been spent in the northwest region of Western Australia, tackling environmental weeds that are incidentally introduced as a result of anthropogenic activities, particularly mine site, gas plant and linear infrastructure development.
In this series of articles I seek to share what I've learned whilst out there 'kicking the dirt' and learning’s from a great many scientists and land management professionals along the way. I've seen firsthand pristine native environments overcome by weed invasion over the course of many years and I've also seen excellent private and public weed control programs successfully contain, control and even eradicate weed issues.
One thing I know for sure is that without early detection, a willingness to act, a sound strategy and the requisite resources in place, then what seemed like a small incursion or non-issue can (usually over a number of growing seasons) deteriorate into a significant, long term problem with serious environmental impact and future financial liability.
Enjoy Part 1 of this series on 'Tackling environmental weeds in Western Australia'.
I hope you get something from these articles and please feel free to contact me if you wish to discuss our capabilities or share your experiences.
Bye for now - Will.
Will Wishart is Managing Director of Astron Environmental Services and has been heavily involved in environmental weed management projects throughout the state of Western Australia for the past fifteen years. He has worked both on the majority of offshore islands, mine sites, gas facilities and conservation areas in the northwest of WA helping to prevent, control and sometimes eradicate invasive plant species.
Part 1 - Environmental weeds and their impact
So what is a weed?
A weed is a plant considered to result in a detrimental effect to economic, social or conservation values of a location (ARMCANZ, ANZECC and Forestry Ministers, 1997). Weeds that impact on conservation values are termed ‘environmental weeds’ and are typically invasive, non‐native plant
species. It’s the fact that it impacts the local environment that defines it as an environmental weed. Weeds that impact on social or economic values are often termed ‘pest plants’ or ‘agricultural weeds’ and may be invasive native or non‐native plants.
Weed species have typically evolved to be excellent survivors and generally reproduce prolifically in the situation where they are considered to be a weed. For example, Buffel grass (Cenchrus ciliaris), is a species of grass native to Africa and India that was, and still is, widely planted as a pasture grass in Australia. Buffel grass is a serious environmental weed in the northwest of WA. Each plant can produce tens of thousands of seeds each lifecycle and remain viable in the soil for many years, probably 8 to10 years in my experience.
Environmental weeds are often excellent at surviving and reproducing in variable conditions and are commonly the first species to colonise and dominate in disturbed environments. Some weeds are of particular concern and, as a result, have been listed for priority management or in legislation. Throughout Australia, weeds are spreading faster than they are being controlled and management of them is consuming an enormous amount of resources. Climate change poses an additional challenge to our ability to manage weeds.
What are the major impacts of weeds?
Few people doubt that the introduction and spread of environmental weeds poses one of the greatest threats to our natural environment and the high level of biodiversity that we are lucky enough to have here in Western Australia. The impact, or consequence, of weed establishment is dependent on relative weed species and asset value characteristics. Most weeds are recognised as a serious threat to the biodiversity, pastoral and social values of the Pilbara region (DoA, 2001).
The presence of environmental weeds diminishes conservation values, and so weed invasion can be viewed as a process that results in what's called 'ecosystem degradation'. Environmental weeds may impact ecosystems in a number of ways, such as:
- Altering the composition and structure of natural vegetation
- Changing geomorphology through the stabilisation or degradation of landforms
- Altering fluvial processes through altering flow and sedimentation
- Changing soil nutrient status
- Introducing exotic diseases
- Hybridisation and genetic modification (of closely related native species)
- Impacting faunal populations as a result of altered food or habitat characteristics, and
- Altering fire regimes including the intensity, frequency and extent of fire.
In my time working in weed management in the Pilbara the clearest impact of environmental weed invasion has been through the altered composition and eventually altered structure of endemic vegetation. Significant vegetation changes such as this are also likely to have affected local fauna populations and to some degree landform stability. Certainly some prolific weed populations have altered fire regimes, which in turn change the natural ecosystem balance.
A bit about invasion dynamics
Weeds proliferate when their traits are advantageous to specific habitats within ecosystems. This may include successful modes of dispersal or life strategies, high productivity, allelopathy or a lack of grazing herbivores. Weeds dispersal occurs through a variety of mechanisms including natural vectors of wind, water, fire and animals; and anthropogenic vectors, such as transport networks and activities associated with urban, commercial, industrial and agricultural land uses.
Weeds are opportunistic, and typically invade areas of soil disturbance and so weed invasion is often viewed as a symptom of increasing ecosystem degradation as much as a cause (Adair and Groves, 1998; Hobbs and Saunders, 1995). Soil disturbance can include physical disturbance as well as changes to soil moisture and nutrient budgets. It may also result from natural factors such as surface water flow, severe weather events or animals.
Areas of drainage lines, wetlands and agricultural are commonly impacted by weed species. Certain weed species are also capable of invading and altering undisturbed habitats and therefore pose a significant threat to biodiversity of otherwise protected conservation assets.
Of course good quarantine and weed hygiene practices are critical for preventing weed spread, however it takes a significant amount of effort and resources to implement effectively. One such situation is the Gorgon Project on Barrow Island, whereby an excellent program was accomplished to largely prevent weed introductions. You can read about the systems and processes in place on that project here. However, similar experiences are hard to find, and for the most part anthropogenic activity results in continued introduction and spread of weeds throughout our environment. In my experience, linear infrastructure vectors such as roads and rail lines pose the biggest threat to weed proliferation throughout our state.
 |
 |
||
| Buffel Grass emerging from underneath a spinifex bush on a Pilbara offshore island. | Ruby Dock seedling growing on a rail embankment. Linear infrastructure is a major vector for weed dispersal and spread. |
Well that's it for Part 1 of this series on 'Tackling Environmental Weeds in Western Australia'.
I hope you stay tuned over the coming weeks for Part 2, Governance of Environmental Weeds. I promise it will be about as exciting as playing Pokemon Go!
References:
Adair, R.J. and Groves, R.H. (1998) Impact of Environmental Weeds on Biodiversity: A Review and Development of Methodology. National Weeds Program. Environment Australia. Canberra. ARMCANZ, ANZECC and Forestry Ministers 1997. The National Weeds Strategy: A Strategic approach to Weeds of National Significance, Canberra.
Department of Agriculture (DoA) 2001. A Weed Plan for Western Australia. Bulletin 4490. State Weed Plan Steering Group. Department of Agriculture, WA.
Hobbs, R.J. and Saunders, D.A. (1995) Invasive Weeds: Prevention is the Key, in Invasive Weeds and Regenerating Ecosystems in Western Australia. Conference Proceedings. G. Burke (ed), Murdoch University, WA.