One of the most significant threats to the biodiversity of the Adelaide Hills is weed invasion. Most of Australia's native vegetation has been invaded at some point since European settlement, or is highly vulnerable to invasion by exotic species. Nationally, invasive plants account for approximately 15% of all flora, and about one-quarter of these are either serious environmental weeds or have the potential to be serious weeds. 
Weeds are essentially species which 'do not belong' in an area. Many plants were intentionally introduced from foreign countries as suitable fodder plants for domestic stock or for soil stabilisation purposes, but most were imported as ornamental garden plants. Even some Australian species have become problematic outside of their natural distribution, including the Sydney Golden Wattle (Acacia longifolia ssp. longifolia), the eastern states Rosemary Grevillea (Grevillea rosmarinifolia) and the Western Australian Bluebell Creeper (Billardiera heterophylla).
Some weeds are prolific invaders of pastures whilst others thrive in bushland communities, out-competing and smothering native plants, and threatening the survival of local native plants and animals. Major infestations have the potential to physically alter the natural state of the bush, by impacting on a number of ecological features including the community structure, natural diversity (species richness), species composition and abundance. There are many examples throughout the Adelaide Hills where bushland has become severely modified by weeds and habitat values are now compromised.
The most common and problematic weeds within the region range from trees, such as Sweet Pittosporum (Pittosporum undulatum), Desert Ash (Fraxinus angustifolius), Olive (Olea europaea), Pine (Pinus radiata), and shrubby, woody weeds including Gorse (Ulex europaeus), Montpellier Broom (Genista monspessulana), Erica (Erica sp.), Boneseed (Chrysanthemoides monilifera) and Blackberry (Rubus fruticosus), to grassy, herbaceous and creeping exotics such as Blue Periwinkle (Vinca minor), Rice Millet (Piptatherum miliaceum), Tangier Pea (Lathyrus tingitanus) and Bulbil Watonia (Watsonia meriana var. bulbifera).
Weeds have been categorised to reflect factors such as invasiveness, potential to spread, 'perceived' and 'actual' impacts and their environmental, economic and social impact. Some of the more common and emerging plants known from the Adelaide Hills Council district fall into one or more of the listed categories.
Click here to download an information sheet on weeds that threaten biodiversity.
 © Commonwealth of Australia (2016) Impact of Weeds
Contacts and useful links
If you suspect that you have a Declared or Weed of National Significance (WoNS) on your land or roadside, contact your nearest Natural Resources Centre or local council for identification and management advice.
NRM Black Hill Office | (08) 8336 0901 (New weed species and Alert Weeds)
NRM District Officer Woodside | (08) 8336 0901 (Declared Weeds on private property)
Adelaide Hills Council Natural Resources Officer | (08) 8408 0400 (Declared Weeds on roadsides and Council land)
Exotic Plant Pest Hotline | 1800 084 881
Plant Biodiversity Centre (State Herbarium) | (08) 8222 9308
Primary Industries and Regional SA (PIRSA) Biosecurity SA Division | alternative common and scientific names for all plants prohibited from sale in South Australia, and a free Weed Control app, which provides information about the control of weeds declared in South Australia.