New weeds will continue to arrive as introductions and naturalise in Australia.

At regional, state and national levels, biosecurity measures are required to address this threat. New weeds arrivals represent a risk over two dimensions:

• Space (geographic location and range)
• Time (rapid or slow invasion)

New weeds can invade slowly, for example, those identified as ‘sleeper weeds’. These weeds-in-waiting are seemingly innocuous and apparently non-invasive, but known to be significant problems elsewhere in the world. Others, for example, agricultural weeds, can invade much more rapidly.

Another form of invasion will come from native plant species shifting their range in response to factors such as fire dynamics, climate change and native vegetation clearing.

The most likely source of new invasive species, both today and under climate change, is neighbouring regions with a similar climate.