Plantlife Volume 50.3 December 2020. South African plants as weeds in Victoria, Australia

 Unwelcome South Africans – reflections on weeds in South-east Australia

 Text and photographs by Richard Boon

It is often said that the second most common threat to biodiversity after habitat destruction is alien species. The source of the claim is Edward O. Wilson’s 1993 book The Diversity of Life. Others argue that the threat is overstated, a myth or even a lie. But the impact can be devastating — in Australia the unique land mammal fauna was decimated after European colonisation and the most likely causes were introduced foxes and cats and altered fire regimes. In this article, I will share some learnings about alien plant management in the state of Victoria using South African weeds as examples [1].

In KwaZulu-Natal some urban areas have very high weed cover but parts of Victoria seem weedier. By 2018 in Victoria at least 1235 taxa were recorded as environmental weeds, that is, plants that invade natural environments. Many more are casuals or ruderals (grow and occasionally reproduce but have not yet established self-sustaining populations) and others are naturalised only in disturbed places. Unfortunately, the number of weedy taxa keeps growing as plants are transported beyond natural boundaries and environmental change promotes new invasions.

Image 1: A weedy grassland on the edge of the Plenty Gorge, Melbourne. The grey plant is Artichoke Thistle and the purple-flowered plant is Pateron's Curse.

I recently moved from Durban to live in suburban Melbourne. Our home is on a 530 m² freehold plot. The climate here is temperate with fairly hot summers and cool winters. Average annual rainfall at home is 740 mm, falling more or less year-round with a small increase in spring and early summer. With our purchase, we inherited a neglected garden full of weeds and a mixed bunch of small trees and shrubs, including the only Rothmannia globosa September Bells I have seen in Melbourne. It flowered beautifully this year. Most homeowners in our suburb maintain their own gardens and verges that, although Council-owned, are our responsibility. Mowing doesn’t excite me so most of our lawn has been replaced with mulch and indigenous plants from nearby nurseries that only stock local species. The makeover was tough work. When we started in February, temperatures frequently reached 35⁰C and the clay soil had hardened and I needed a pick to dig even a small hole. Planting is not advised until the autumn break when the first decent rainfall exceeds evaporation and plants can grow again but eager to make progress, I dived in. At first, it felt weird planting eucalypts, wattles, banksias and hakeas but I find I am getting used to them.

No matter how thorough you are, follow up is essential. Ironically three of my most challenging problems are South African – Ehrharta erecta Panic Veldt-grass, Oxalis pes-caprae Soursob and Romulea rosea Onion-grass. E. erecta grows all year and I remove it by hand-pulling, while Onion-grass and Soursob are dormant in summer and can be controlled from late winter to spring. Pulling these geophytes leaves bits behind so they must be dug up carefully (this isn’t viable with Soursob which has many easily-dislodged bulbils), solarised (covering and heating soil) or sprayed carefully with glyphosate. I try to minimise spraying since damaging our first Passionfruit vine. In the first winter and spring, drifts of iris volunteers, including Freesia, Gladiolus, Ixia and Sparaxis, emerged from dormancy and flowered. These are all minor environmental weeds but I have left them for now because they are beautiful and remind me of home. My nostalgia gives me an insight into why acclimatisation societies were formed to 'improve' the local flora and fauna and make new places more like home. Victoria’s was established in 1861 and survived only 11 years by which time many highly invasive species like rabbits were well established. The iris species at home pose no risk because the seed can’t reach native bushland and material I dispose of is destroyed. I may change my mind once the indigenous plants are better established.

Image 2: Oxalis pes-caprae Soursob in a Melbourne nature reserve. This species can form extensive mats excluding smaller plants.

Image 3: There are squillions of Romulea rosea Onion-grass plants in Victoria making it one of the most numerous weeds.  

There is no legal requirement to remove many weeds because lists included in legislation in Australia seems less comprehensive than in South Africa and states (= provinces) have their own legislation. In Victoria the primary legislation dealing with weeds is the Catchment and Land Protection Act (1994) in terms of which weeds can be declared as ‘noxious’ because they may cause environmental or economic harm. There are four categories of noxious weeds and listed plants are classified into one of the categories for each catchment region. Many weeds that threaten the environment are not listed because they may have values in other contexts or the legislation has not kept pace with the threat on the ground.

The federal (= national) government has identified 32 priority species, referred to as Weeds of National Significance (WONS). The WONS were selected in consultation with state governments based on their invasiveness, potential for spread and environmental, social and economic impacts and whether they can be successfully managed. Included are six South African Asparagus species, two subspecies of Chrysanthemoides monilifera, Lycium ferocissimum, Senecio madagascariensis, and Vachellia nilotica (= Acacia nilotica). Australians call V. nilotica, which is a serious weed in semi-arid parts of the country, Prickly Acacia. This seems a poor name given it fits most African acacia species, the spines are technically not prickles and many Australian wattles have ‘spiny’ modified phyllodes and stipules.

Image 4: Bridal Creeper (Asparagus asparagoides) with ripe fruit and starting to die back in November.

The local patches where I spend the most time, are Greswell Forest and Plenty Gorge. Both are fairly degraded with a reasonable eucalyptus overstorey and a degraded understorey. At Greswell the main vegetation type is Plains Grassy Woodland that is dominated by River Red-gum Eucalyptus camaldulensis. This is the most widespread species of Eucalyptus in Australia and the most aggressively invasive in South Africa. At Plenty Gorge there are various woodland and forest types.Chrysanthemoides monilifera subsp. monilifera African Boneseed is a common weed in the Gorge. C. monilifera subsp. rotundata Bitou Bush is well-established in New South Wales and attempts have been made to eliminate a couple of Victorian populations. Also at Plenty Gorge, Aizoon pubescens Galenia is abundant in disturbed areas and forms extensive grey-green mats to the exclusion of other species.

Image 5: River Red-gum in Plains Grassy Woodland. The understorey is almost 100% Phalaris aquatica, a grass species from Southern Europe which is invasive in Australia and South Africa. 

Image 6: African Boneseed in spring fringeing an abandoned quarry. 

Asparagus asparagoides Bridal Creeper is common in both areas and is widespread in southern Australia. It is a major threat because it invades several environments, including undisturbed habitats, it smothers smaller plants and its dense mass of rhizomes and tubers prevent germination by native species. By early summer it is deciduous and the red berries ripen on yellowing plants. Control is very difficult without biological control agents. Fortunately, there are three and the Bridal Creeper Rust (a fungus) and a leafhopper have been widely introduced by community groups. Interestingly there are apparently two forms of Bridal Creeper in southern Australia, known as the common form and the Western Cape form. The latter may be a different species with larger leaves and a longer growing season. It seems to be resistant to the rust. Even commoner are Ehrharta longiflora Annual Veldt-grass and E. erecta. At Greswell, Zantedeschia aethiopica White Arum-lily and its cultivar ‘Green Goddess’ grow along the creek lines along with the smaller and less invasive Mediterranean arums Arum italicum Italian Arum and Arisarum vulgare Cobra Lily or Friar’s Cowl. Ruderals found here include Aloe maculata Soap Aloe, Crassula multicava subsp. multicava Fairy Crassula, C. tetragona subsp. tetragona Mini Pine Tree (another descriptive but to me silly name) and Dimorpotheca fruticosa Trailing African Daisy.

Image 7: White Arum-lily in a small wetland growing with an introduced Nasturtium species.

Image 8: Fairy Crassula on a road verge growing with Mini Pine Tree uprooted and placed on a fence. Pieces will eventually drop to the ground and root again.

When Covid-19 permits, my work includes monitoring sites established to offset native vegetation losses across the State. I also provide management advice to landowners. By 2008 at least 50% of Victoria’s native vegetation had been cleared of alien species and in some fertile areas only 0.1% of the original vegetation remains. About 4000 ha of native vegetation is still lost every year and current drivers include land clearing for settlement and conversion of native pastures to croplands. Overall rates of vegetation loss have slowed as new regulations have been introduced with the policy objective of no net loss of biodiversity due to the destruction of native vegetation. Regulations requiring that unavoidable native vegetation loss is offset are included in all planning schemes. Applicants for permits can create offsets on their own properties or purchase credits from a register. Offsets are established in perpetuity and must be managed in terms of an agreement that includes a management plan. Payments are made annually to compliant offset site owners for 10 years (by which time the native vegetation condition has in theory improved to maintenance levels) to fund the management and compensate for forgoing other land-uses.

One of the most widespread and commonly seen woody weeds on offset sites is Lycium ferocissimum African Box-thorn. Besides displacing native vegetation, this species provides harbour for rabbits and foxes and food for foxes. On one coastal site that I visited, mature plants of Polygala myrtifolia Polygala had been controlled to low numbers but there were still hundreds of little seedlings to be removed. Two commonly encountered South African daisies are Arctotheca calendula Capeweed and Gazania linearis Gazania, with the latter more often seen around habitation although also spreading into natural areas.

Image 9: African Box-thorn is common in bushland where it is sometimes the only shrub under a eucalypt canopy.

Image 10: Capeweed can be abundant on abandoned farmland and in less disturbed sites. Here creating a Namaqualand-like scene in county Victoria

With so many species to eliminate or control and the usual resource limitations, it helps to know what risk each species poses in order to focus management and get the best return on investment. A state-wide risk rating has been determined for each taxon based mainly on the stage of the invasion process (i.e. how much further it may spread), rate of spread and impact on native ecosystems. The list will be updated as new taxa become weedy, more information becomes available and environmental conditions change. For example, Tecomaria capensis Cape Honeysuckle has established at a handful of sites around Melbourne and in the east of Victoria. It was recently found about 100 km west of Melbourne by a natural resource management crew employed under the State’s Covid-19 relief programme. While the species is considered to be ‘currently non-invasive’, plants will be treated as a precaution.

When I provide advice at sites, I use the list to focus work on the species that pose the most threat. Interestingly, many of the listed species are Victorian or Australian weeds that have expanded their ranges through horticulture. Perhaps the most common are wattles and Pittosporum undulatum Sweet Pittosporum, which is also a weed in South Africa. Many of these wattles are also weeds in South Africa, e.g. Acacia baileyana Cootamundra Wattle, A. cyclops Western Coastal Wattle, A. decurrens Early Black Wattle, A. longifolia subsp. longifolia Long-leaved Wattle and A. saligna Orange Wattle. Where the species are indigenous to Victoria (as opposed to other states), a conservation work exemption is required for their removal as they are classified as native vegetation. Determining the original range of these species can be tricky and the regulations aim to minimise unwarranted removal. I don’t recall as many South African plants being considered weeds outside of their natural ranges (the term extralimital is sometimes used).

Image 11: Long-leaved Wattle is very common in the Grampians National Park where it displaces the native understorey plants.

In conclusion, for many species and areas the weed problem seems insurmountable and on-ground control works appear inadequate. There is nothing like South Africa’s world-renowned Working for Water programme, for example. A lot of the work seems to be done by community groups and private landowners with adjacent state land often less well managed. The legislation only deals with a small subset of weeds. On the other hand, there are very good resources for identifying weeds, describing best-practice control and for prioritising management efforts and I think South Africa could improve in these areas. It is also my impression that biosecurity is taken much more seriously here and more effort is made to prevent potentially invasive organisms from establishing and spreading. This is a very wise investment strategy at any scale, country, state or site, as Benjamin Franklin said: “an ounce of intervention is worth a pound of cure”.

References used

Department of Jobs, Precincts and Regions, 2020, Consolidated lists of declared noxious weeds and pest animals, https://agriculture.vic.gov.au/biosecurity/protecting-victoria/legislation-policy-and-permits/consolidated-lists-of-declared-noxious-weeds-and-pest-animals (accessed 2 November 2020)

Department of Environment, Land, Water and Planning, 2017, Protecting Victoria's Environment – Biodiversity 2037, https://www.environment.vic.gov.au/__data/assets/pdf_file/0022/51259/Protecting-Victorias-Environment-Biodiversity-2037.pdf (Accessed 2 November 2011)

Department of Land, Environment, Water and Planning, 2020, Native Vegetation,https://www.environment.vic.gov.au/native-vegetation/native-vegetation (accessed 2 November 2020)

Department of Land, Environment, Water and Planning, 2020, Early Invader Weeds Update Issue #20, Friends of WESI: Weeds at the Early Stage of Invasion Project, https://www.environment.vic.gov.au/__data/assets/pdf_file/0024/491307/Early-Invader-Weeds-Update_Winter_20_2020.pdf (accessed 2 November 2020)

Hirsch, H., Allsopp, M.H., Canavan, S., Cheek, M., Geerts, S., Geldenhuys, C.J., Harding, G., Hurley, B.P., Jones, W., Keet, J., Klein, H., Ruwanza, S., Van Wilgen, B.W., Wingfield, M.J. & Richardson, D.M., 2019, Eucalyptus camaldulensis in South Africa – past, present, future, Transactions of the Royal Society of South Africa, DOI: 10.1080/0035919X.2019.1669732

Museums Victoria, Acclimatisation Society of Victoria, https://collections.museumsvictoria.com.au/articles/1803 (accessed 2 November 2020)

Office of Environment and Heritage, 2013, Asparagus weeds management manual: current management and control options for asparagus weeds Asparagus spp. in Australia, Office of Environment and Heritage (NSW), Sydney.

Weeds Australia, 2020, Weeds of National Significance (WONS), https://weeds.org.au/weeds-profiles/ (accessed 2 November 2020)

White, M., Cheal, D., Carr, G. W., Adair, R., Blood, K. and Meagher, D., (2018), Advisory list of environmental weeds in Victoria, Arthur Rylah Institute for Environmental Research Technical Report Series No. 287. Department of Environment, Land, Water and Planning, Heidelberg, Victoria.

Wilson, E.O., 1992, The Diversity of Life, Cambridge, MA: Harvard University Press.

Woinarski, J.C.Z., Burbidge, A.A. & Harrison P.L., 2015, Ongoing unravelling of a continental fauna: Decline and extinction of Australian mammals since European settlement, PNAS Vol. 112 no. 15 4531–4540.

About the author: Richard is a practical botanist with well over 30 years’ field experience, having first worked for the Conservation Division of the Wildlife and Environment Society. He worked for the eThekwini Municipality for nearly 20 years and was Manager of the Biodiversity Planning Branch of the Environmental Planning and Climate Protection Department from 2005 to 2018. Richard is the author of Pooley's Trees of Eastern South Africa: a Complete Guide. 2010. Flora and Fauna Publications Trust, Durban, South Africa. He currently lives in Melbourne, Australia where he works for the state government.

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[1] Common names in this article are those usually used for the weeds in Victoria, Australia.