Literature review: Impact of Chilean needle grass ... - Weeds Australia

species tend to be those which transform the system invaded by rapidly modifying the prevailing disturbance regime (Richardson
and van Wilgen 2004). Transformer species often have disproportionately large effects compared to other weeds because they
become numerically dominant in the invaded area or dominate the biomass. Good examples of transformer species are Mimosa
pigra L. in Melaleuca woodlands in northern Australia (Braithwaite et al. 1989), Tradescantia in New Zealand forests (Kelly
and Skipworth 1984) and Pinus and Acacia species in South Africa (Versfeld and van Wilgen 1986). Transformer grasses
include ‘land builders’ such as Spartina (Gray et al. 1997), and Andropogon gayanus (Kunth) in northern Australia, which has
massive stature in comparison to native grasses and greatly enhances the intensity and frequency of fires (Rossiter et al. 2003,
Ferdinands et al. 2006).
Impact of N. neesiana
N. neesiana does not neatly fit the definition of transformer species in Australian native grasslands. It dominates the canopy in
many invaded native grasslands, although its morphology, biomass and phenology is similar to some of the major native grasses
that it replaces. The invaded systems remain as grasslands, and other effects it may cause are poorly known.
The biodiversity impacts of N. neesiana in temperate Australian natural grasslands is probably critically determined by its
presence and impact in the cultural steppe that surrounds and fragments the remaining indigenous remnants. The success of N.
neesiana in the cultural steppe drives propagule pressure, so determines, in part, the susceptibility of grassland remnants to
invasion. Their invasibility is also strong influenced by their health or degradation state, which is critically influenced by
management. The prevalence of major anthropogenic disturbance and the disruption of ‘natural’ disturbance patterns appear to
be central issues. A range of other factors most likely contribute to the success of N. neesiana in native grasslands and its
biodiversity impact, including release from natural enemies.
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