The next generation of invasive plants

The study of plant invasions has usually focused on plants adapted to colonizing areas immediately after a disturbance (early successional species or “weeds” by some definitions). An example of this, is the seminal work of Herbert Baker, with his list of traits to explain why some species become weeds and others do not (e.g. fast growth, production of lots of seeds, good dispersal.). So why do late-successional species (for example, forest understory species) not invade? The answer is: we did not look close enough - they indeed invade!! This is the point of a paper by Patrick Martin and collaborators, who study forests – which are usually known as “invasion resistant systems” – and the colonization of exotic shade-tolerant species in them. Their central point is that there have been larger numbers of introductions of early successional species compared to late successional species (or shade tolerant), and that forest dynamics are much slower than other systems (e.g. a forest gap must be created for a species that need disturbances to colonize). And it is for these reasons that we associate invasive plants solely with early successional species, and we see forests as invasion-resistant systems. We are now observing many highly invasive plants that are not disturbance dependent. These may be a lot harder to control and could have important detrimental effects on native communities.

Patrick H. Martin, Charles D. Canham, Peter L. Marks (2009). Why forests appear resistant to exotic plant invasions: intentional introductions, stand dynamics, and the role of shade tolerance Frontiers in Ecology and the Environment DOI: 10.1890/070096