Gamba Grass is probably the single greatest threat to tropical savannas, a vitally important Australian ecosystem made up of native grasses in an open woodland.
 
This foreign invader (or invasive grass) builds up fuel to a level which encourages much hotter fires, which kill the native trees, which are a feature of the landscape. The whole area is transformed from a vibrant, healthy savanna into an ugly blanket of weeds.
 
See the article on the 2005 ISC Froggatt Award