Transformer Weeds
Transformer weeds can be defined as invasive species which have the capacity to undermine the ecological processes which maintain the health of native vegetation and hence the habitat of indigenous plants and animals.
Of the weeds which Mount Alexander landholders often identify as being the main problem weeds on their properties, the following can be regarded as transformer weeds in native vegetation:
Asparagus asparagoides Bridal Creeper – capable of engulfing all understorey vegetation, inhibiting germination and establishment of all other species by creating a continuous subterranean mat of fleshy tubers resembling an Echidna.
Briza maxima Large Quaking-grass – the most serious exotic annual grass which can invade bushland throughout the region, adding to the flammability of the understorey at ground level.
Crataegus monogyna Hawthorn – develops exceedingly tough and penetrating taproots soon after germination, ultimately capable of dominating understorey vegetation.
Ehrharta longiflora Annual Veldt-grass – another exotic annual grass which contributes to the flammability of understorey vegetation.
Genista monspessulana Cape Broom or Montpellier Broom – amasses a seed bank in the soil resulting in explosive population increase after each fire event, thereby outcompeting native vegetation.
Juncus acutus Spiny Rush or Sharp Rush – capable of invading grassy woodlands, riparian vegetation, seasonal and permanent freshwater wetlands and saline and subsaline wetlands.
Lycium ferocissimum African Box-thorn – heavy infestations shade out and prevent regeneration of all other species, harbouring rabbits which also prevent recruitment of native species.
Nassella neesiana Chilean Needle-grass – can invade grassland and grassy woodland to the complete exclusion of all native species and arguably one of the most intractable invasive exotics in South-eastern Australia.
Oxalis pes-caprae Soursob – can dominate the herb layer of invaded sites in a wide range of habitats to the exclusion of all other species.
Phalaris aquatica Toowoomba Canary-grass – an aggressive invader of a wide range of grassland, woodland, forest, riparian and wetland habitats, ultimately excluding all other species.
Rubus species Blackberry – principally Common Blackberry Rubus anglocandicans (open farmlands and roadsides), Forest Blackberry Rubus polyanthemus (shady lowland forests) and Cut-leaf Bramble Rubus laciniatus (shady mountain forests) – capable of infiltrating open forests and woodlands, ultimately outcompeting all other plants, with the latter two species even capable of invading shady forests.
Salix X rubens Basket Willow – dense rootlet mats trap sediment thereby choking stream bed microhabitats, increasing turbidity, altering stream flow and temperature regime.
Ulex europaeus Gorse or Furze – can form impenetrable thickets which exclude native species, harbour rabbits and increase fire risk.
Each of these species is listed as a very serious threat to one or more vegetation formations in Victoria by Geoff Carr in Environmental Weed Invasions in Victoria: conservation & management implications (1992).