Background
In regard to potential climate-induced range shifts of arable weeds in Europe, the authors write that "range expansion of harmful C4 weeds common in Central Europe into the boreal region is considered to be a potential risk." But they state that the range shifts predicted by bioclimatic envelope modelling (e.g. Araujo and Peterson, 2012) underestimate the importance of biotic interactions, noting that "range expansion of a plant species requires successful population establishment in its range margin (Alexander and Edwards, 2010), meaning that arable weed species should be able to colonize cultivated fields, including both C3 and C4 crops, in the boreal region," which feat "calls for consideration of the impact of elevated temperature on crop-weed interactions."

What was done
In exploring this subject in greater depth, Hyvonen and Ramula "studied the impact of a 3°C elevation in temperature on the establishment and maintenance of populations of two annual C4 weeds (Amaranthus retroflexus and Echinochloa crus-galli) with and without a competing C3 (barley) or C4 (maize) crop," based on data obtained from a number of field and glasshouse experiments they conducted.

What was learned
The two Finlanders report discovering that "competition of a weed with a crop appeared to be a more important factor for limiting the maintenance of weed populations than elevation in temperature, as neither of the weed species was able to maintain populations in competition with crops," noting that "even an increase in the frequency of warm years did not result in viable weed populations establishing."

What it means
As a result of their extensive research dealing with the weeds-vs.-crops question, Hyvonen and Ramula conclude that weed "range expansion predictions based on climate envelope models, neglecting biotic interactions, have likely been overestimated."

References
Alexander, J.M. and Edwards, P.J. 2010. Limits to the niche and range margins of alien species. Oikos 119: 1377-1386.

Araujo, M.B. and Peterson, T. 2012. Uses and misuses of bioclimatic envelope modeling. Ecology 93: 1527-1539.