Native Environmental Weeds of Western Australia

Thirteenth Australian Weeds Conference The enemy within: native environmental weeds of Western Australia 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 plants 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 Calothamnus 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, Hakea costata Meisn., of these ferns are native species but occur readily Hakea pycnoneura 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, Calothamnus validus be accepted as natural. S.Moore and Calothamnus quadrifidus 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 Banksia woodland corridors via vehicles or soil, e.g. Senecio lautus in Koondoola Regional Park from amenity plant- 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 Conospermum 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

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