Herbicide drift impact on floral resources and pollination services: A landscape approach
Synthetic auxin herbicide resistant crops have been deregulated by the US Environmental Protection Agency for use in the 2015 growing season to address agricultural producer challenges with herbicide resistant weeds. These new crop traits will likely cause a significant increase in synthetic auxin herbicide use in corn and soybean, which increases the risk of herbicide drift injuring non-target plant communities and associated insect fauna in adjacent field edges. To explore the impact of herbicide drift on landscape scale ecosystem service provisioning in the Mid-west USA, we used the Lonsdorf landscape pollination model to quantify pollination services under a variety of herbicide drift scenarios in landscapes varying in land use and proportion of edge habitat. We selected 20 counties as sentinel landscapes that vary in the proportion of county area planted with corn or soybeans from a population of 623 counties across seven states. In these sentinel landscapes, floral resources and pollination services were quantified with the Lonsdorf model at a 30m resolution considering five scenarios of herbicide exposure.
Across the Midwestern USA, field edge area ranged from less than one to nine percent of the total landscape with an average of 4%. The “edgiest” landscapes were those with approximately 40% of the landscape planted to corn and soybean. The Lonsdorf model projected large spatial variation in pollination services across and within the sentinel landscapes, but much greater variation across landscapes than within a landscape due to the imposed herbicide scenarios. The largest effects of synthetic auxin herbicide use on pollination services were projected in areas with the largest proportion corn and soybean. At drift-level herbicide doses the floral resource and pollination service provisioning capacity of the landscape was reduced by approximately 10% in landscapes with more than 50% corn and soybean. Herbicide treatment of field edges with label doses resulted in more than 20% reduction of landscape scale pollination services. Several parameters that strongly influenced the model results, e.g. plant sensitivity to herbicide drift and baseline habitat resource values, are not well understood, and require further study. Overall, the simulation results highlight the landscape context dependency of the impact of herbicide treatments, and that the landscape context should be included in herbicide drift risk assessment, deregulation, and biodiversity conservation policy.