Crops vs. Weeds at the Northern Edges of Their Current Ranges
Hyvonen, T. and Ramula, S. 2014. Crop-weed competition rather than temperature limits the population establishment of two annual C4 weeds at the edge of their northern range. Weed Research 54: 245-255.
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. Results indicated 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."
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."
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.