Climate Change and the Geographic Distribution of Damaging Agricultural Weeds: Are Big Changes in Store?.

By the end of the century, climate change projections under a business-as-usual emissions scenario suggest a globally-averaged warming of 2.4 – 6.4 ° C.  If these forecasts are realized, agricultural systems are likely to experience significant geographic range transformations among damaging endemic weed species and new vulnerabilities to exotic weed invasions. To anticipate these risks and to devise management strategies for proactively addressing them, it is necessary to characterize the environmental conditions that make specific weed species abundant, competitive, and therefore damaging to crop production.  Maize forms the most extensive agroecosystem in the United States with approximately 93 million acres planted in 2007.  In this study, US maize is used as a model system to explore the implications of climate change on the geographic distribution of damaging agricultural weeds.    At the scale of US states, space-for-time substitution was used to suggest the magnitude of change among damaging weed communities.  Additionally, bioclimatic range rules were derived for two widely-distributed weeds (Sorghum halepense L., Abutilon theophrasti L.) to demonstrate how the geographic distribution of specific species may evolve over the next century.  Results suggest that the composition of damaging weed communities may be radically altered by climate change.  Regions such as the Northeast may prove particularly vulnerable with few, if any, species of present-day importance retained.  In contrast, regions like the mid-South are likely to experience fewer shifts even with a similar magnitude of climate change.  By the end of the century in the Corn Belt, cold-tolerant species like A. theophrasti may be of minor importance whereas S. halepense, a predominantly southern US weed at present, may become common and damaging to maize.  The projected emergence of novel climate niches in the southern US suggests new vulnerabilities to exotic weed species that are not currently established in the United States.