Invasive plants and invaded ecosystems in Australia: implications for biodiversity

Exotic, invasive plants are a major cause of environmental degradation throughout Australia, affecting most ecosystems and vegetation types. Here, we investigate the origins of Australia’s exotic plant flora, assess their economic and ecological impact and discuss the processes by which these species become successful invaders. Various management strategies and legislative measures designed to minimise the impact of weeds on native biodiversity are also examined. Most exotic invaders have been deliberately introduced to the Australian landscape via two main pathways – horticulture and agriculture – and many are taxonomically distinct, with no native Australian relatives. Following their introduction a proportion of these species have become naturalised, forming self-sustaining populations in the landscape. Approximately 10% of this naturalised pool of species have gone on to become serious invaders, capable of displacing native vegetation. We discuss the competing theories about how species make the transition along the ‘invasion continuum’, including the role of functional traits, introduction effort, propagule pressure, residence time and community susceptibility to invasion. We also consider the major functional types of exotic invaders (e.g. woody weeds, vines and scramblers, perennial grasses) and discuss the impacts and management challenges unique to each. Which exotic plants are in Australia and how did they get there? Invasion by exotic plant species is recognised globally as one of the greatest threats to biodiversity (Millennium Ecosystem Assessment, 2005). This is equally true in Australia where exotic plants across a wide range of habitats significantly reduce native species abundance and diversity, contributing to extinction risk. Australia is particularly vulnerable to invasion by introduced plants due to its isolation and consequent unique biota, and few ecosystems in Australia are immune from invasion (Adair & Groves, 1998; Groves et al., 2005).