A comparison of the herbicide tolerances of rare and common plants in an agricultural landscape

Authors: Egan Jr, John; GRAHAM, IAN - Pennsylvania State University; MORTENSEN, DAVID - Pennsylvania State University

Submitted to: Environmental Toxicology and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2013
Publication Date: 1/31/2014
Citation: Egan Jr, J.F., Graham, I.M., Mortensen, D.A. 2014. A comparison of the herbicide tolerances of rare and common plants in an agricultural landscape. Environmental Toxicology and Chemistry. 33(3):696–702. doi:10.1002/etc.2491.

Interpretive Summary: Wildflowers and other plants growing in farming landscapes can have many benefits for sustainable agricultural systems, such as supporting pollinators. Agricultural plant diversity has been declining in many regions globally, and herbicide pollution is often suggested as a key cause. If herbicide pollution is an important factor, then we would expect plant species that are common and thriving in an intensively farmed region to show higher tolerance to frequently used herbicides than rare or declining plant species. In this study, we compared the tolerance of common and rare plant species from Lancaster County, PA, to three different herbicides. We found that common and rare species generally had similar tolerances, suggested that other changes in farming systems - such as expanding field sizes and clearing of habitat fragments - may be more important for plant conservation than herbicide pollution.

Technical Abstract: Declining plant biodiversity in agroecosystems has often been attributed to escalating use of chemical herbicides, but other changes in farming practice including the clearing of semi-natural habitat fragments confound the influence of herbicides. In this paper, we introduce a new approach to evaluate the impacts of herbicide pollution on plant communities at landscape or regional scales. If herbicides are in fact a key factor shaping agricultural plant diversity, we would expect to see the signal of past herbicide impacts in the current plant community composition of an intensively farmed region, with common, successful species more tolerant to widely-used herbicides than rare or declining species. By comparing data from an extensive field survey of plant diversity in Lancaster County, Pennsylvania, U.S., with herbicide bioassay experiments in a greenhouse, we tested the hypothesis that common species possess higher herbicide tolerances than rare species. We treated five congeneric pairs of rare and common species to three commonly used herbicide modes of action in bioassay experiments and found few significant differences in the tolerance of rare species relative to common species. These preliminary results suggest that other factors beyond herbicide exposure may be more important in shaping the distribution and abundance of plant species diversity across an agricultural landscape.