module 17C
Integrated weed management in natural ecosystems
Objectives
At the end of this module, you will be able to:
- be familiar with the integrated management of weeds in natural ecosystems
- be able to be able describe the principles of integrated weed management in natural ecosystems
- explain the impact of different weed management methods
on natural ecosystems.
Module Outline
- Aims of IWM in natural ecosystems
- IWM and revegetation in natural ecosystems
- Summary
- References and further reading
Aims of IWM in natural ecosystem
There might be a number of reasons why weeds of natural ecosystems
need managing. In the past, environmental
weeds were only considered a problem if they threatened to invade economically
valuable pasture systems. However, today environmental areas are valued for
aesthetic reasons or as sites of biodiversity. The following reading considers
the impact of environmental weeds and the aims of environmental weed management.
You should note carefully the three aims of environmental weed management and
the additional considerations of these.
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IWM and revegetation in natural ecosystems
Some basic principles underlie the development of an integrated weed management strategy for natural ecosystems:
- the impact of specific control techniques on the suite
of environmental weeds present at a site needs to be understood. We need to
identify:
- control techniques most suitable to a problem weed
- whether the control techniques interact in a compatible manner (e.g. spraying herbicide in a manner that does not kill biocontrol agents) - the impact of control techniques on the native flora and the ecosystem must be considered. There is no value in implementing strategies which will prove detrimental to the native vegetation in the long-term (e.g. herbicides that also kill seedlings of native plants)
- revegetation techniques should be integrated with the control strategy rather than adopted subsequent to control.
It is important to consider revegetation as a tool that aids in weed control, as well a desirable end point. The integrated control-revegetation strategy should aim for a compromise that encourages the:
- establishment of desirable native species, yet simultaneously
- discourages the re-establishment of existing dominant weeds and
- prevents the incursion of new weed problems.
The value of an integrated approach is to develop techniques that reinforce each other to achieve the ultimate goals of:
- long-term weed control
- ecosystem stability
- restoration
The following reading discusses the range of weed management methods available for environmental systems and provides a number of case studies. You should particularly note the emphasis on revegetation. Some of the management strategies are discussed in more detail below; however, even when used in an integrated package, such controls will not provide long-term management of weeds without revegetation.
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Biological and chemical controls
The detailed principles underlying chemical and biological control have been presented in Modules 13 to 15. With respect to environmental weeds, the same considerations for non-target plants apply. The biological and chemical controls applied within natural ecosystems must be extensively tested under quarantine conditions or field trials to ensure that they have minimal impact upon non-target native species and no long-term residual effects on the environment.
Given this, chemicals have been use to manage bitou bush on a broad scale on the NSW coast. This strategy takes advantage of the sensitivity of bitou bush to glyphosate and appliction of herbicide when native species are least affected. The strategy is described in detail in the following two readings.
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Biological control is correctly identified as the most important control method for environmental weeds. However, it needs to be remembered that it can take a long time to be effective. As the following reading demonstrates, biological control activities against Hypericum perforatum (St. John's wort) began in Australia in the 1920s. Substantial success against St. John's wort has only been seen in the past 5 years. The reasons for this delay are many, but demonstrate that other control methods are important.
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Cultural control
Fire
The use of fire is particularly relevant to controlling environmental weeds in natural ecosystems as the regeneration ecology of many native species is closely tied to fire. Fire also has the advantage of being relatively cheap to apply over large areas infested by environmental weeds.
The following readings describe situations where fire has
been used to aid management of woody weeds. There are somewhat contrasting results
in the two situations; however, both studies conclude that fire alone does not
provide effective management. You should note that in both situations fire has
greatly diminished the soil seedbank, making subsequent management easier.
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An understanding of the biology of the weed species can make fire even more useful. For example, if the weed species germinates primarily in winter, whereas natives do not germinate until spring, an autumn fire can provide the opportunity to implement additional management to weed before native species emerge from the soil. A spring burn under these circumstances will be counter productive.
Other cultural controls
Other cultural controls that may be applied include:
| Control method | Details |
| cutting and mowing | Tends to be labour-intensive; many degraded natural habitats are relatively inaccessible, thereby making cutting by hand or machine impractical |
| grazing | Most national parks do not allow
grazing by stock. Grazing by feral animals as well as by native animals
certainly occurs and this may present additional problems for the manager
of public land trying to control environmental weeds such as horehound.
Where environmental weeds occur on private land and where there is a possibility of control through grazing, this should be encouraged. Consideration should be given to the relative palatabilities of the weed and native species to stock. If weeds are unpalatable or toxic to stock, then grazing is not necessarily a valid option as the removal of more palatable native species will only improve the competitive advantage of the weeds. Stock may also be used to trample down tall standing herbaceous weeds and thereby allow smaller native seedlings to establish, as in some thistle-invaded natural grasslands for example |
| burning | |
| hand-pulling | In many weed-infested areas of public land close to cities, large numbers of volunteers may be used to hand-pull seedlings of environmental weeds such as bitou bush and boneseed. Seedlings and young plants of the weedy species can be removed in this way with minimal disturbance to the surrounding vegetation. Light infestations are usually treated first. Such methods, though localised, may be highly effective and comprise an important aspect of overall integrated management systems for environmental weeds |
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Regardless of the type of strategy adopted, a major feature of successful integrated control strategies is to employ proper and persistent follow-up procedures. It is usually insufficient, for instance, to spray, hand-pull or burn only once or even several times. Management needs to be employed continually. This also applies to biocontrol agents that may need to be released continually and widely to facilitate their establishment.
The seeds of many environmental weeds may persist for up to a decade or be dispersed widely. Therefore, long-term, if not continual, monitoring of a weed’s abundance and spread coupled with appropriate longer-term management is required to ensure that weeds remain in check and growth and development of the native species are encouraged.
Summary
Weed management in natural ecosystems has for long had a fragmented approach, frequently with local ‘Friends’ groups doing what they could to manage weed incursions. A major hope has been the use of biological control agents; however, these are frequently targeted against weeds of economic importance, for example weeds of pastures.
It is only in fairly recent years that the general public and policy makers have come to appreciate the value of native ecosystems; however, it is almost impossible to put a dollar figure on this value. A number of strategies are available for use in integrated management of weeds and rehabilitation of natural ecosystems; however, our understanding of the basic biology and ecology of the weeds targeted can be poor.
References and further reading
Adair, RJ 1995, ‘The threat of environmental weeds to biodiversity in Australia: a search for solutions’, in RA Bradstock et al (eds), Conserving biodiversity: Threats and solutions, Surrey Beatty & Sons, Chipping Norton, NSW pp. 184-201.
Adair, R & Shepherd, R, (eds) 1991, ‘Control of Environmental Weeds’, Proc. 3rd Symposium on Control of Environmental Weeds, Monash University, 6-7 November 1991, Plant Protection Quarterly vol. 6, pp. 95-153.
Buchanan, R 1989, Bush regeneration: Recovering Australian landscapes, Student Learning Productions, TAFE NSW, Sydney.
Carr, GW, Yugovic, JV & Robinson, KE 1992, Environmental weed invasions in Victoria, conservation & management implications, Vic. Dept Conservation and Environment & Ecological Horticulture, Melbourne.
Carter, R 1997 ‘Strategies and planning for weed control’, in Proceedings of the 9th Biennial Noxious Weeds Conference, NSW Agriculture, Goulburn, Vol. 1, pp. 9-15.
Groves, RH 1989, ‘Ecological control of invasive terrestrial plants’, in JA Drake et al. (eds), Biological Invasions. A Global Perspective, John Wiley & Sons, Chichester, pp. 437- 461.
Groves, RH & Burdon, JJ, (eds) 1986, Ecology of Biological Invasions: An Australian Perspective, Australian Academy of Science, Canberra.
Groves, RH, Shepherd, RCH & Richardson, RG, (eds) 1995, The Biology of Australian Weeds, vol. 1, RG & FJ Richardson, Frankston.
Humphries, SE, Groves, RH and Mitchell, DS 1992, ‘Plant invasions of Australian ecosystems. A status review and management directions’, Kowari, vol. 2, pp. 1-134.
Parsons, WT & Cuthbertson, EG 1992, Noxious weeds of Australia, Inkata Press, Melbourne.
Spennemann, DHR & Allen, LR 2000, ‘Feral olives (Olea europaea) as future woody weeds in Australia: a review’, Australian Journal of Experimental Agriculture, vol. 40, pp. 889-901.
Vranjic, JA, Woods, MJ & Barnard, J 2000, ‘Soil-mediated effects on germination and seedling growth of coastal wattle (Acacia sophorae) by the environmental weed, bitou bush (Chrysanthemoides monilifera ssp. rotundata)’, Austral Ecology, vol. 25, pp. 445-453.
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