Considerable strides have been made in the new
domain of plant invasion ecology.
The three key questions are:
- what
makes some species more invasive than others?;
- what
makes ecosystems resistant or susceptible to invasions?;
- how can
we use insights from the previous questions to manage
invasions?
Scientists continue to rely heavily on the track
record of various species as aliens in order to predict their
invasiveness (explaining why some species are more invasive than
others), rather than on mechanistic understanding of invasions.
Problems with this approach include the fact that only a small
proportion of the world’s flora has been widely planted as
aliens, and for long enough, to gauge their invasiveness. Fewer
than half of the currently invasive plant species have a track
record of being invasive elsewhere.
Species known to have invaded many parts of the
world are obviously more likely to invade in other areas, but no
prediction can be made for species that have no history of
widespread introduction over long periods, or evidence of their
invasiveness. Nonetheless, it seems that risk assessments based
largely on the experience of other invasive species are still the
most pragmatic approach in predicting invasiblity worldwide. In any
event, continuing global changes will complicate any
predictions.
There is slow progreas towards a more mechanistic
understanding of invasiveness, contributing to the debate on
whether it is feasible or desirable to aim for standardized
criteria for all weed lists, given that such lists serve different
purposes in different parts of the world. Formal protocols for
assessing the risk of invasiveness are not widely applied.
Australia and New Zealand are the only countries using risk
assessment models in day-to-day decision-making when evaluating
applications for permission to introduce new species.