Alien plant invasions are getting more widespread
and serious at an alarming rate around the world. Many more species
are becoming invasive, more processes are being disrupted, more
ecosystems damaged, and more costs are being incurred. There are
now many images of devastating invasions, including entire
landscapes dominated by single invasive alien species. Some of the
most damaging invaders were virtually unknown even a few decades
ago. Notable in this category is the Old World climbing fern
(Lygodium microphyllum), which has invaded southern Florida at
astonishing speed.
Some of the lesser known aspects are:
- The
complexity of real-life systems was highlighted using quantitative
food-web models. These show that changes in species composition
caused by plant invasions could have serious consequences for
higher trophic levels, and may greatly affect organisms at levels
that have no direct connection with the invasive plant species in
question.
- A
phenonemon dubbed ‘invasional meltdown’, meaning
synergistic interactions between invasive species that promote
further invasions and exacerbate their detrimental effects.
- Various
elements of global change (global warming, elevated atmospheric CO2
, nitrogen deposition, habitat fragmentation) are already
interacting to worsen the impacts of plant invasions. Some
experimental results suggest that elevated CO2 levels have already
had a marked effect on traits of some key invasive species in North
America: increased biomass production, expanded leaf area and
spininess, and enhanced pollen loads.
All of these traits, alone or in combination,
affect how these plants influence native species, and the
invasibility of the ecosystems they occupy.
