Pollination Needs and Diverse Bees of a Prospective Fuelbreak Wildflower, Curlycup Gumweed (Grindelia squarrosa)(Asteraceae)

Authors: CANE, JAMES - Wildbeecology; Love, Byron; Burrows, Skyler; Fortin, Alexander; Graham, Kelsey

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2025
Publication Date: 7/28/2025
Citation: Cane, J., Love, B.G., Burrows, S., Fortin, A.P., Graham, K.K. 2025. Pollination Needs and Diverse Bees of a Prospective Fuelbreak Wildflower, Curlycup Gumweed (Grindelia squarrosa)(Asteraceae). Rangeland Ecology and Management. 102:186-192. https://doi.org/10.1016/j.rama.2025.06.016.
DOI: https://doi.org/10.1016/j.rama.2025.06.016

Interpretive Summary: The arid sagebrush steppe of the U.S. Intermountain West is prone to immense and costly wildfires. For wildfire mitigation, land managers are clearing linear fuel breaks to distrupt fire progression across the landscape. These fuel breaks are often planted with a non-native plant (forage kochia) that is wind pollinated. An alternative plant that is native to the region and could support pollinators is desirable. A good option is a native fire-resistant plant, curlycup gumweed, that readily colonizes disturbed sites. It also blooms late in the summer when flower resources for bees are otherwise scarce. However, the pollination needs of this plant and what bees will visit it has not previously been investigated. Our field experiments found that bee visitation is essential for its pollination, with many more viable seeds produced when bees are able to visit the flowers. We also found that a diverse community of bees visits the flowers of this plant (23 genera from five families). Most visiting species nest below ground, where their progeny are safe from the surface heat of fire. If this species is to be used as a seeded fuel break throughout the region, abundant bee visitors will be necessary to produce ample seed. In turn, once curlycup gumweed is established in fuel breaks it will provide both pollen and nectar over many weeks that native bees avidly collect and cache for their progeny, as well as feeding future queens of resident social species.

Technical Abstract: The arid sagebrush steppe of the U.S. Intermountain West is prone to immense and costly wildfires. To disrupt the continuity of flammable vegetation, regional public land managers have begun clearing linear fuel breaks that are then currently being seeded to a wind-pollinated Asian forb, forage kochia. A native fire-resistant alternative, Grindelia squarrosa, readily colonizes disturbed sites, where it offers a profusion of late-season flowers to native bees. Field experiments showed that bee visitation is essential for its pollination. Compared with geitonogamous selfing, outcrossing yielded 4-fold more filled achenes that were twice as likely to germinate. Our 13 regional surveys of bees foraging at G. squarrosa flowers was diverse (23 genera from five families) and all native but for honeybees. Most species and ¾ of individuals nest below ground, where their progeny are safe from the surface heat of fire. Because G. squarrosa is a biennial, pollination by wild bees will be needed to assure ample seed to perpetuate populations seeded in fuel breaks of the US sagebrush steppe. In turn, G. squarrosa offers both pollen and nectar over many weeks that native bees avidly collect and cache for their progeny, as well as feeding future queens of resident social species.