Enhancing Floral Resources for Pollinators in Harvested Conifer Forests of the Pacific Northwest

Abstract Harvested forests have the potential to support pollinator conservation, particularly when enhanced with native flowers, yet their conservation value remains largely untapped and undetermined. Because bee diversity and abundance are closely linked to the diversity and abundance of flowers, our study examined the effectiveness of floral enhancements seeded in wildfire-affected harvested forests in Oregon’s Cascade Mountains, US. We assessed the richness, abundance, cover, floral availability, and persistence of 20 native plant species sown in two contexts: burned slash piles and harvested forest stands. We also compared floral abundance and richness of pollinator-visited floral species in enhanced areas to unaltered areas within stands. We found that sowing native seeds into burned slash piles was an effective strategy for establishing floral enhancements, supporting greater species richness, plant abundance, cover, and floral abundance than enhancements seeded directly into harvested stands. Floral enhancements in burned slash piles persisted for at least three years, providing statistically significantly more pollinator-visited floral resources than unenhanced areas within the stand. Averaging across the second and third years post-seeding, these enhancements supported 5.3 times more pollinator-visited floral species and 8.9 times more total blooms per unit area than unenhanced harvested stands. Compared to unenhanced burned slash piles, enhancements produced 8.2 times more pollinator-visited floral species and 51 times more flowers per unit area. Study implications: Our findings highlight the potential of seeding floral enhancements in burned slash piles as a practical strategy for integrating pollinator conservation into forest management practices. Our approach proved more effective than seeding directly into harvested stands, where competition from existing vegetation and weedy species diminished enhancement success. Successful germination and growth of native flowering plants in burned slash piles, coupled with the persistence of several native species over multiple years, suggested this method may provide valuable resources for increasing stand biodiversity, including direct opportunities for benefiting pollinator conservation.