Establishing forbs for pollinators in agricultural landscapes of the Great Plains

Authors: Rinella, Matthew - Matt; Porensky, Lauren; Bellows, Susan - Bartlett; Knox, Jeanne; METIER, EMILY - Natural Resources Conservation Service (NRCS, USDA)

Submitted to: Restoration Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2022
Publication Date: 12/8/2022
Citation: Rinella, M.J., Porensky, L.M., Bellows, S.E., Knox, J.M., Metier, E.P. 2022. Establishing forbs for pollinators in agricultural landscapes of the Great Plains. Restoration Ecology. 31(4). Article e13846. https://doi.org/10.1111/rec.13846.
DOI: https://doi.org/10.1111/rec.13846

Interpretive Summary: Pollinators are in decline, partly because grasslands containing the wildflowers these insects feed on have been converted to row crops. Well over 1 million ha of Great Plains cropland have been seeded with wildflowers to stem the decline of pollinators, but the success of these seeding efforts is unclear. In this study, we quantified factors regulating wildflower abundances in 120 former crop fields seeded by managers in semi-arid lands of Colorado and Montana. Our data indicate a need to improve wildflower establishment. Seeded wildflower cover was <10% in most fields, and no seeded wildflowers were observed in 23% of fields. Our data also indicated avenues for increasing wildflower abundances. High weed and seeded grass densities reduced wildflower cover, and weeds reduced the probability wildflowers were observed. Several past studies indicate certain herbicides sometimes benefit seeded wildflowers, and further study might identify consistently beneficial herbicides. Instead of beneficial herbicides, managers sometimes applied risky herbicides before seeding that likely persisted in soil and reduced wildflower establishment. Seed rates were too low to maximize wildflower abundances, and much money was wasted on seeds of species that did not establish. We identified several species with relatively high establishment probabilities that will support most pollinators. For now, these species should be seeded at high rates. Lower rates could become sufficient if effective weed control is implemented.

Technical Abstract: Pollinators are in decline, partly because grasslands containing the forbs these insects feed on have been converted to row crops. This land conversion has been extensive in the Great Plains, which is concerning because many imperiled pollinators reside there, as do 40% of U.S. honeybees. Well over 1 million ha of Great Plains cropland have been seeded with forbs to stem the decline of pollinators, but the success of these seeding efforts is unclear. In this study, we quantified factors regulating forb abundances in 120 former crop fields seeded by managers in semi-arid lands of Colorado and Montana. Our data indicate a need to improve forb establishment. Seeded forb cover was <10% in most fields, and no seeded forbs were observed in 23% of fields. Our data also indicated avenues for increasing forb abundances. High weed and seeded grass densities reduced forb cover, and weeds reduced the probability forbs were observed. Several past studies indicate certain herbicides sometimes benefit seeded forbs, and further study might identify consistently beneficial herbicides. Instead of beneficial herbicides, managers sometimes applied risky herbicides before seeding that likely persisted in soil and reduced forb establishment. Seed rates were too low to maximize forb abundances, and much money was wasted on seeds of species that did not establish. We identified several species with relatively high establishment probabilities that will support most pollinators. For now, these species should be seeded at high rates. Lower rates could become sufficient if effective weed control is implemented.