AIM : We develop a framework for quantifying invasions based on lagged trends in invasions
(―invasion debt‖) with the aim of identifying appropriate metrics to quantify delayed
responses at different invasion stages — from introduction to when environmental impacts
LOCATION : Worldwide; detailed case-study in South Africa
METHODS : We define four components of invasion debt: the number of species not yet
introduced but likely to be introduced in the future given current levels of introduction /
propagule pressure; the establishment of introduced species; the potential increase in area
invaded by established species (including invasive species); and the potential increase in
impacts. We demonstrate the approach in terms of number of species for 21 known invasive
Australian Acacia species globally, and estimate three components of invasion debt for 58
Acacia species already introduced to South Africa by quantifying key invasion factors
(environmental suitability, species invasion status, residence time, propagule pressure, spread
rate and impacts).
RESULTS : Current global patterns of invasive species richness reflect historical trends of
introduction—most acacia species that will become invasive in southern Africa have already
invaded, but there is a substantial establishment debt in South and North America. In South
Africa, the likely consequence of invasion debt over the next 20 years was estimated at: four
additional species becoming invasive with an average increase of 1075 km2 invaded area per
invasive species. We estimate that this would require over US$ 500 million to clear.
Main conclusions: Our results indicate that invasion debt is a valuable metric for reporting
on the threats attributable to biological invasions, that invasion debt must be factored into
strategic plans for managing global change, and, as with other studies, they highlight the value of proactive management. Given the uncertainty associated with biological invasions,
further work is required to quantify the different components of invasion debt.
Walker, Gareth A.; Robertson, Mark P.; Gaertner, Mirijam; Gallien, Laure; Richardson, David M.(Springer, 2017-12)
Invasive trees are a major problem in South Africa. Many species are well established whereas others are still in the early stages of invasion. The management of invasive species is most cost effective at the early stages ...
Novoa, Ana; Le Roux, J.J. (Johannes Jacobus); Robertson, Mark P.; Wilson, John R.U.; Richardson, D.M. (David Mark), 1958-(Oxford University Press, 2015)
Understanding which species are introduced and become invasive and why are central questions
in invasion science. Comparative studies on model taxa have provided important insights, but
much more needs to be done to ...
Faulkner, Katelyn T.; Robertson, Mark P.; Rouget, Mathieu; Wilson, John R.U.(Elsevier, 2014-11)
Biosecurity schemes aim to prevent the introduction of species with a high invasion
potential, without unduly restricting personal freedom and commercial activities. But
invasive species risk assessments are time consuming, ...