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Invasions of Alien Plant Species: Spurred on by Global Warming?
Volume 16, Number 33: 14 August 2013

In a paper recently published in Plant Ecology, Verlinden et al. (2013) note that "it is widely suggested that climate warming will increase the impact of biological invasions," yet they state that "studies on the combined effect of these two global changes [climate warming and biological invasions] are scarce." And, therefore, to help fill this real-world data void, they set about to investigate the effect of an experimentally-induced temperature increase on mixes of highly-invasive alien plant species and their native competitors.

Utilizing six sunlit climate-controlled chambers at the University of Antwerp, the three Belgian researchers grew three species pairs of alien-invasive/native-competitor plants - (1) Fallopia japonica/Cirsium arvense, (2) Solidago gigantea/Epilobium hirsutum, and (3) Senecio inaequidens/Plantago lanceolata - either together or in isolation at ambient air temperature (TA) or elevated air temperature (TE = TA + 3°C), all of which treatments were supplied with equal amounts of water.

In the first two of these three sets of plants, the native species dominated when grown in mixture with the alien-invasive plants, while in the third pair the alien-invasive species dominated; and warming did not modify the competitive balance in any of the three mixed pairs. However, and most interestingly, Verlinden et al. report that, to their knowledge, in the only study to examine the combined effects of higher temperatures and simultaneously elevated atmospheric CO2 concentrations on an invasive/native set of plants, the "positive effect of experimental warming on invader growth disappeared under elevated CO2 concentrations," citing the work of Hely and Roxburgh (2005). And in another such study that we have reviewed on our website, Bradford et al. (2007) [] found that the elevated CO2 treatment "did not modify the effects of the invasive species on [the] native plant assemblages."

Although the experimental results cited above deal with but a few sets of alien-invasive/native-competitor plants, they do seem to favor the native-competitor plants in the majority of situations that appear to have been studied, suggesting - at a minimum - that widely-expressed concerns about the possibility of CO2-induced global warming increasing the negative impacts of alien plant invasions has, as yet, no compelling basis in pertinent experimental studies.

Sherwood, Keith and Craig Idso

Bradford, M.A., Schumacher, H.B., Catovsky, S., Eggers, T., Newingtion, J.E. and Tordoff, G.M. 2007. Impacts of invasive plant species on riparian plant assemblages: interactions with elevated atmospheric carbon dioxide and nitrogen deposition. Oecologia 152: 791-803.

Hely, S.E.L. and Roxburgh, S.H. 2005. The interactive effects of elevated CO2, temperature and initial size on growth and competition between a native C3 and an invasive C3 grass. Plant Ecology 177: 85-98.

Verlinden, M., Van Kerkhove, A. and Nijs, I. 2013. Effects of experimental climate warming and associated soil drought on the competition between three highly invasive West European alien plant species and native counterparts. Plant Ecology 214: 243-254.