Invasion by woody shrubs and trees
The invasion of many habitats by exotic shrubs and trees has been an important factor causing changes in Australian native vegetation through declines in species richness, changes to community composition and reducing ecosystem function (Lindsay and French 2004; Gosper eta!. 2006; Mason and French 2007; Gooden et at. 2009). Costs of management have been high (Sinden et a!. 2004) and research into management options extensive. Whilst management-oriented research places Australia at the leading edge ofthe field (Briese 2004), this has been at the expense of research testing hypotheses about mechanisms of invasion in Australia. Information on the novel distribution, population dynamics and ecology of the majority of invasive species is largely unknown. Ten species of exotic woody shrub or small tree are among the 20 Weeds ofNational Significance (WoNS) classified by the Australian Federal Government, reflecting their extensive current and/or projected impact on native and agricultural communities. Funding for weed research is largely focused on these WoNS but directed specifically to the development of successful management options. Very little is directed to understanding invasion or impacts. Additionally, a further 100 shrubs and trees (and more herbs, grasses and vines) are known as significant environmental weeds and described in a range ofland management resources (e.g. http://www.weeds.org.au). Almost nothing is understood about these species. Many invasive shrubs and trees have invaded from horticultural stock, and the species may differ from native stock (e.g. Lantana camara L., lantana, Figure 13.1) causing difficulties in both management and in understanding ecological consequences.