Thirteenth Australian Weeds Conference

The enemy within: native environmental weeds of

Greg Keighery Department of Conservation and Land Management, PO Box 51, Wanneroo, Western Australia 6065, Australia

Summary In Western Australia thirty fi ve species of of native forests. Current serious invaders include: Western Australian have become naturalised, Leptospermum laevigatum (Gaertn.) F.Muell, Euca- largely outside their ranges, from plantings. Fifty four lyptus maculata Hook., Eucalyptus citriodora Hook., eastern Australian species are also naturalised and Brachychiton populneus (Schott & Endl.) R.Br., Aca- several form a major threat to the forests of Western cia decurrens Willd., A. dealbata Link., A. pycnantha Australia. Current major WA environmental weeds Benth., A. longifolia (Andrews) Willd., A. melanoxylon are Agonis fl exuosa and Chamelaucium uncinatum. R.Br. and Pittosporum undulatum Vent. These species An improved knowledge of the ecology, nature and should not be used in or near bushland as amenity composition of the native fl ora is required to prevent plantings or promoted as garden subjects. an increasing threat of native weeds. As native plants are not considered weeds the bio- Keywords Western Australia, eastern Australian geographic and taxonomic issues that restrict exotic environmental weeds, revegetation, status, hybridi- importations to WA do not apply. Therefore, eastern sation. Australian natives should be assessed for weediness in the same manner as exotics INTRODUCTION One of the problems in recognising and controlling Uncertainty about the status of some species There environmental weeds in Australia is an understanding are at least 18, mostly wetland species that are vari- that Australian native species can be serious problems ously listed as native or naturalised depending on the out of their natural ranges and habitats. reference used. These require genetic, ecological and During this century there will be an increasing taxonomic study to clarify their origins and status. focus on replanting and rehabilitating degraded lands Examples include: Acacia farnesiana (L.) Willd., to restore ecosystem functions, connect remnants and Datura leichhardtii Benth., Physalis minima L., create a sustainable agricultural system. For example Grammatotheca bergiana (Cham.) C.Presl., Juncus current proposals in Western Australia (WA) are to bufonius L., Salsola tragus L., Chenopodium glaucum replant one million hectares over 10 years and to L., Tribulus terrestris L. and Bromus arenarius Labill. create new perennial agricultural systems using both More detailed discussion of these taxa can be found Australian native and introduced species (Government in Kloot (1986) and Romanowski (1998). of Western Australia 2000) to help control rising saline Some species listed as weeds in Western Australia groundwaters in the agricultural zone. are considered native in eastern Australia. Examples include: Pseudognaphalium luteo-album (L.) Hilliard METHODS & Burtt, Samolus valerandi L., Solanum americanum While there are adequate requirements to test the Mill. Romanowski (1998) gives strong evidence for potential weediness of new exotic introductions for considering Berula erecta (Huds.) Coville as native, agriculture, there are no such requirements for native stating on p. 14 that this species has ‘sometimes species. Using a series of headings, this paper will been regarded as introduced, but there are enough discuss and illustrate the nature, depth and scope of differences between the Australian and European the issues around native species as weeds. These ex- plants for it to be uncertain whether they are the same amples are derived from many years of observation in species’. Similarly for Lythrum hyssopifolium L. he Western Australia. noted ‘pollen evidence for occurrence in Australia for over 20,000 years’. RESULTS AND DISCUSSION There are few species regarded as natives to Weedy eastern Australian natives in Western Aus- Western Australia and weeds in eastern Australia, tralia A large range of eastern Australian ornamental, e.g. Cotula coronopifolia L. (Romanowski 1998) timber and tannin species were planted around forestry ‘This species has long been regarded as native, but it settlements from 1900 onwards. Over 54 species have is now increasingly listed as exotic; however, there is since established feral populations and several of these no strong evidence either way.’ species are on the verge of becoming major weeds

93 Thirteenth Australian Weeds Conference

Perhaps unique to Western Australia are a series of weeds. Normally as Low (2001) noted they are delib- species with native forms in the tropics, but with exotic erately translocated plants because many more species weedy forms in temperate Western Australia. These in- and individuals are translocated. This is also the case clude: Cynodon dactylon (L.) Pers., Cyperus rotundus in Western Australia where amenity or enrichment L., Melia azedarach L., Euphorbia australis Boiss. and plantings, roadverge revegetation mixes and arboreta E. drummondii Boiss., Homalanthus novo-guineensis have contributed most of the weed records. (Warb.) Lauterb. & K.Schum., Cyperus polystachyos Examples of species from enrichment plantings Rottb., Colocasia esculenta (L.) Schott and Hibiscus that are now escaping include: trionum L. These species are generally listed as either a) Ceratopteris thalictroides (L.) Brongn. at Mill- native or naturalised for the entire taxon in Western stream, Acacia blakelyi Maiden, Acacia micro- Australian checklists. botrya Benth. and Acacia lasiocalyx Andrews, Finally there are also truly native species that are chrysantherus F.Muell., Agonis disturbance opportunists. They include species with: flexuosa, Chamelaucium uncinatum Schauer, a) Unknown natural ranges: examples are Azolla Allocasuarina huegeliana (Miq.) L.A.S.Johnson, fi liculoides Lam. and Azolla pinnata R.Br. Both Melaleuca lanceolata Otto, costata Meisn., of these ferns are native species but occur readily Meisn. in Kings Park, Kunzea in man made habitats (dams and ponds). They are baxteri (Klotzsch.) Schauer and Melaleuca dios- now rarely encountered in the wild. There seems mifolia Andrews at Bluff Knoll in Stirling Range no doubt that their current range does not refl ect National Park. their natural range, however, our lack of detailed b) Acacia myrtifolia (Sm.) Willd., Calothamnus survey means that new records of occurrence will graniticus Hawkeswood, be accepted as natural. S.Moore and R.Br. b) Expanding natural ranges as suitable habitats have been widely used recently as road side occur: these can be dispersed by biological plantings and for revegetation purposes and are agents such as birds: Lemna disperma Hegelm., already localised escapes. Some of these spe- Gratiola pubescens R.Br., Bolboschoenus cald- cies have proved highly invasive in very short wellii (V.J.Cook) Sojak, Ruppia species and Ottelia time periods, for example, Friends of Koondoola ovalifolia (R.Br.) Rich. Bushland have removed over 5000 seedlings of c) Dispersing by human assistance along transport Calothamnus quadrifi dus from woodland corridors via vehicles or soil, e.g. Senecio lautus in Koondoola Regional Park from amenity - Willd., Boerhavia coccinea Mill. and Boerhavia ings less than 15 years old. The species has also schomburgkiana Oliv. self seeded into Warwick Open Space and Kings d) Invaders of naturally and artifi cially disturbed Park from roadside plantings. areas; these may be unpalatable weeds of graz- c) Surveys of old townsites and arboreta have docu- ing and pastoral lands, e.g. Pteridium esculentum mented another 13 species that are self-seeding (G.Forst.) Cockayne; weeds of marginal agricul- within these locations. There are another fi ve spe- tural lands, Ptilotus polystachyus (Gaud.) F.Muell., cies that have established feral populations after Podotheca gnaphaloides Graham and Muehlen- being introduced in soil along roads or railroads beckia adpressa (Labill.) Meisn. or abundant (Acacia fl agelliformis Court, Acacia lasiocarpa post-fi re species such as Acacia saligna (Labill.) Benth., Acacia myrtifolia (Sm.) Willd., Acacia Wendl. and Agonis fl exuosa (Willd.) Sweet which pulchella R.Br. and huegelii are enhanced by controlled burns and/or frequent R.Br.). fi re regimes. Because there has not been widespread plantings of The fi rst two groups are normally recorded as natives Western Australian natives till recently, we can only in fl oras and checklists, and members of the last two list those species that at the few sites known are seri- either as weeds or natives, depending on the view of the ously invasive and cause major structural changes to recorder. Resolution of the above issues are required plant communities that they invade. These species are: to ensure we do not waste resources on controlling Agonis fl exuosa, Allocasuarina huegeliana, Chame- unique native forms of widespread species or invest laucium uncinatum, Hakea costata, Hakea pycnoneura resources in control when disturbance management and Melaleuca lanceolata. is the key. These species should also not be used in or near bushland as amenity plantings or in general seed Western Australian native plants weedy in West- mixes. ern Australia There are native species that are truly

94 Thirteenth Australian Weeds Conference

Hybridisation between local and non-local species exotic introduction is. Eastern Australian species and variants Biodiversity consists of three levels: established here in natural ecosystems should be the community, species and the underlying genetic eradicated or controlled as a priority. architecture of those species. Weedy Western Australian 2. To combat and manage Western Australian native native species impact on the fi rst two levels, but not environmental weeds we need to understand the to the same extent as weedy exotic species. To the ecology (including appropriate disturbance third level, poorly planned revegetation schemes and regimes), and biogeography of our amenity plantings could have the greatest long-term native fl ora. Native weed management requires effect. In Kings Park, plantings of non-local forms and a holistic approach. species of Acacia pulchella, Anigozanthos manglesii 3. With increasing attempts to replant areas and D.Don, Eucalyptus ficifolia F.Muell. (hybridising rehabilitate degraded lands the use of non-local with Marri, Eucalyptus calophylla R.Br.) and E. material (especially the use of generalist or gomphocephala DC. have resulted in many hybrid ‘chook mixes’ along transport routes) should genes present in these species (Coates et al. 2002). be discouraged. The compilation and access to This has also shown to be the case at Bold Park records of known weediness in native species is where planted Chamelaucium uncinatum is hybridising important. We also need to compile locations of with genetically and morphological distinct local native signifi cant local variants where generalist plantings forms (Barrett et al. 1999). Similarly hybridisation is will enhance hybridisation and potential loss. Both widely occurring between the frequently planted river of these data sets are important in ensuring that red gum (Eucalyptus camaldulensis Dehnh. and the solutions do not cause more problems than they local river gum (Eucalyptus rudis Endl.). This may be are attempting to fi x. detrimental to the genetic integrity of this species as a whole over time. REFERENCES Unnatural disturbance itself is bringing together Barrett, M.D., Krauss, S.L., Dixon, K.W. and Consid- different ecotypes that are normally separate by ine, J.A. (1999). Molecular ecology of Chamelau- subtle habitat differences and providing habitats for cium uncinatum (Geraldton Wax). In ‘Ecological hybridisation offspring to survive and spread, e.g. Connections, ESA 99 Handbook’, eds R.T. Wills, Acacia pulchella at Eagle Bay, near Busselton. S. Yates and R.J. Hobbs, p. 37. Western Australia is world renowned for its fl oral Coates, D., Keighery, G.J. and Broadhurst, L. (2002). diversity, which is underpinned by a vast array of Morphological and genetic variation in Tuart. localised genetic and morphological variants. Poorly Proceedings of the Tuart Workshop. Wildfl ower planned rehabilitation, revegetation and amenity will Society of Western Australia. simplify these complex communities by stealth as well Government of Western Australia (2000). Natural as direct competition. Resorce Management in Western Australia: The Salinity Strategy for Western Australia. State RECOMMENDATIONS Salinity Council, Perth. There is the potential for major problems to Kloot, P.M. (1986). Checklist of the introduced species emerge at all levels of biodiversity conservation in South Australia. South Australian Department involving native species as weeds in natural and of Agriculture Technical Bulletin No. 14. degraded ecosystems. The following is recommended Low, T. (2001). A challenge to our values: Australian to reduce naturalisation and incursion of eastern plants as weeds. Plant Protection Quarterly 16, Australian species: 133-135. 1. We should treat all eastern Australian species as Romanowski, N. (1998). Aquatic and wetland plants: A exotics, not as natives, for weed management. fi eld guide for non-tropical Australia. (University They should be screened for weediness as any of New South Wales Press, Sydney).

95