Introduction of the nature reserves
The Mount Painter Nature Reserve is located in the landscape of central Canberra and neighbour to Black Mountain. It includes Mount Painter, a segment of lowland bush and the Wildflower Triange. In total, there are 114 native species and 86 introduced plant species on Mount Painter (Ginniderra Catchment Group, n.d.). The Isaacs Ridge Nature Reserve is located in south Canberra. There is a pine plantation in this nature reserve. Both two sites are important habitats for native species such as Yellow box (Eucalyptus melliodora), Galash (Eolophus roseicapilla) and Speckled warbler (Chthonicola sagittata). Both reserves are managed by the ACT Government and assisted by local organisations and a small group of volunteers who carry out a variety of tasks aiming at increasing the biodiversity of the reserve and enjoyment for all the users of the reserve. Weeding is one of the activities.
I have been volunteering with the Conservation Volunteer Canberra in these two sites and helping with some general conservation works, especially weeding.
An overview of weeds in this two reserves
We focused on removing Horehound (Marrubium vulgare L.) and Sweet briar (Rosa rubiginosa) in the two sites respectively (as shown in figure 1 and figure 2). Both species are invasive weeds in Australia but their habitats are largely different.
Horehound is a noxious weed imported from Europe and achieving its maximum potential distribution in south Australia (Weiss, et al., 1999). Though seed of horehound prefers moisture and warm area, grown horehound is very drought-tolerant. In addition, leaves of this species contain marrubin, a bitter alkaloid, which makes it unpalatable for grazing animals (Weiss, et al., 1999). Hence, without predator, horehound spread quickly and in south Australia.
Different from horehound, sweet briar is mainly distributed in plantation which is well-drained and moderately fertilised in our volunteering sites (Anon., 2014). The grown sweet briar can be very large and hard to be hand-removed. In monoculture and high diversity plantings, there is little competition and light grazing. The invasive, woody weeds can invade the system quickly and will reduce the richness of planted species. Several studies have proved that without hand-weeding, the diversity planted species will decline in abundance and the efficiency of planting is largely reduced. (Dickson & Gross, 2015)
Figure 1. Horehound (Marrubium vulgare L.)(Source:http://ourherbfarm.com/herbs/horehound.php).
Figure 2. Sweet briar (Rosa rubiginosa)(Source: http://canberranaturemap.org/Community/Sighting/31304)
In Australia, the number of kangaroos, sheep and rabbits has increased considerably in recently years. They all aid in the transport of the seeds of weeds to new areas. Also, over-grazing of these species can further remove native or planted species and aggravate the invasion of weeds.
Table 1. Potential impacts of environmental weeds on indigenous ecosystems (Williams & West, 2000)
|Competition with indigenous plants for light, nutrients, moisture, pollinators, and they smother or crowd the soil.|
|Replacement of indigenous plant communities.|
|Prevention of natural regeneration.|
|Change in the movement of water in both soil and watercourses.|
|Increase of soil erosion by shading out ground plants which would normally hold the surface soil together.|
|Change in the shape of the land (e.g. different grass types on coastal sand dune systems may introduce poisons into the soil which prevent other plants growing around them, or they poison animals).|
|Provision of food and/or shelter for pest animals (and some indigenous animals).|
|Change in water quality or characteristics (e.g. willow species, Salix), and habitat for fish and other aquatic animals.|
|Introduction of foreign genes into local plant populations by cross breeding (hybridization and gene swamping).|
|Change in fire behaviour by altering characteristics such as the quantity and distribution of fuel.|
|Alteration of disturbance regimes.|
Figure 3. Developed root of Horehound
Weed has dominated the two conservation sites in the natural reserves. As it shows in figure 3, the root of Horehound can be very developed.
Some invasive species may consequently increase fire intensity as well which will negatively affect the grown species and regeneration. Weeds can greatly increase fuel load in an area and make it difficult to predict the frequency and effects of prescribed fire and wildfire.
The intensified fire can be up to 300℃ hotter than fires in nearby native-dominated areas, and seeds in the soil might be destroyed by the fire (Emery, et al., 2011).
Social & economic effects
The communities and individuals usually have little incentives to control weeds especially weeds in the wild areas. Because weeds could only bring very limited economic benefits while cost a lot to remove and control. The net benefit which is the difference between the income and cost is below 0 which means extra money is spent on controlling weeds.
In 2005, the Australian government spent at least $116.4m on control, monitor and manage weeds, and about 75% of the fund is used to inspection, research and extension. However, there is still little data on the distribution of weeds in natural environments, and the economic loss caused by weeds is hard to be estimated (Sinden, et al., 2005).
Hand-weeding using tools like mattock or garden scissor is the most common in general conservation, especially for weeds at their ages (see Figure 4). For woody weeds like Sweet briar that are difficult to be uprooted, hard chemical is sprayed to the root area immediately after cutting its stream in order to suppress its growth.
Figure 4. Weeds removal using mattock
Figure 5. Garden scissor and poison for killing weeds
Control, monitoring and collecting data of environmental weeds is of great social, economic and environmental importance. According to Weiss et al.(1999), communication has been proved to be able to promote weed management in the future. Communities and individuals play an important role in the further management. As it is discussed above, individuals have little awareness and knowledge about weeds. Many people cannot distinguish between weeds and native grass. Hence, education and promotion are also critical success factors.
Anon., 2014. NSW Department of Primary Industries. [Online]
Available at: http://weeds.dpi.nsw.gov.au/Weeds/Details/137
Dickson, T. L. & Gross, K. L., 2015. Can the Results of Biodiversity-Ecosystem Productivity Studies Be Translated to Bioenergy Production. PLoS ONE, 10(9).
Emery, S. E., Uwimbabazi, J. & Flory, L., 2011. Fire intensity effects on seed germination of native and invasive Eastern deciduous forest understory plants. Forest Ecology and Management, p. 1401–1408.
Ginniderra Catchment Group, n.d. Mount Painter, Canberra: s.n.
Sinden, J. et al., 2005. The economic impact of weeds in Australia. Plant Protection Quarterly, 20(1), pp. 25-32.
Weiss, J., Sagliocco, J. & Wills, E., 1999. A Comparison Between European And Australian Populations of Horehound. Twelfth Australian Weeds Conference.
Williams, J. A. & West, C. J., 2000. Environmental weeds in Australia and New Zealand: issues and approaches to management. Austral Ecology, Volume 25, p. 425–444.
Author: Wenjia Lai (u5491307)
Date of working: 18/09 & 07/10