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Volume 33, Issue 5 e2855
ARTICLE

Bee diversity decreases rapidly with time since harvest in intensively managed conifer forests

Rachel A. Zitomer

Rachel A. Zitomer

Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon, USA

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Sara M. Galbraith

Sara M. Galbraith

Department of Forest Engineering, Resources & Management, Oregon State University, Corvallis, Oregon, USA

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Matthew G. Betts

Matthew G. Betts

Department of Forest Ecosystems and Society, Oregon State University, Corvallis, Oregon, USA

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Andrew R. Moldenke

Andrew R. Moldenke

Department of Botany and Plant Pathology, Oregon State University, Corvallis, Oregon, USA

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Robert A. Progar

Robert A. Progar

USDA Forest Service, Sustainable Forest Management Research, Washington, District of Columbia, USA

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James W. Rivers

Corresponding Author

James W. Rivers

Department of Forest Engineering, Resources & Management, Oregon State University, Corvallis, Oregon, USA

Correspondence

James W. Rivers

Email: [email protected]

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First published: 11 April 2023
Citations: 13
Handling Editor: Jacob R. Goheen

Abstract

Despite widespread concerns about the anthropogenic drivers of global pollinator declines, little information is available about the impacts of land management practices on wild bees outside of agricultural systems, including in forests managed intensively for wood production. We assessed changes in wild bee communities with time since harvest in 60 intensively managed Douglas-fir (Pseudotsuga menziesii) stands across a gradient in stand ages spanning a typical harvest rotation. We measured bee abundance, species richness, and alpha and beta diversity, as well as habitat characteristics (i.e., floral resources, nesting substrates, understory vegetation, and early seral forest in the surrounding landscape) during the spring and summer of 2018 and 2019. We found that bee abundance and species richness declined rapidly with stand age, decreasing by 61% and 48%, respectively, for every 5 years since timber harvest. Asymptotic estimates of Shannon and Simpson diversity were highest in stands 6–10 years post-harvest and lowest after the forest canopy had closed, ~11 years post-harvest. Bee communities in older stands were nested subsets of bee communities found in younger stands, indicating that changes were due to species loss rather than turnover as the stands aged. Bee abundance—but not species richness—was positively associated with floral resource density, and neither metric was associated with floral richness. The amount of early seral forest in the surrounding landscape seemed to enhance bee species richness in older, closed-canopy stands, but otherwise had little effect. Changes in the relative abundance of bee species did not relate to bee functional characteristics such as sociality, diet breadth, or nesting substrate. Our study demonstrates that Douglas-fir plantations develop diverse communities of wild bees shortly after harvest, but those communities erode rapidly over time as forest canopies close. Therefore, stand-scale management activities that prolong the precanopy closure period and enhance floral resources during the initial stage of stand regeneration will provide the greatest opportunity to enhance bee diversity in landscapes dominated by intensively managed conifer forests.

CONFLICT OF INTEREST STATEMENT

The authors declare no conflicts of interest.

DATA AVAILABILITY STATEMENT

Original and processed data (Zitomer, Galbraith, Betts, Progar, & Rivers, 2023) are available on Dryad at https://doi.org/10.5061/dryad.pzgmsbcq9. Voucher materials (Zitomer, Galbraith, Betts, Moldenke, et al., 2023) are available in the Oregon State Arthropod Collection (osac.oregonstate.edu) under accession no. OSAC_AC_2023_01_09-001-01. Forest disturbance spatial layers from Clary, 2020. National Land Cover Database imagery from Dewitz, 2019. Digital elevation model raster from Farr et al., 2007. Additional data sets and literature sources used for species trait determination are described in Appendix S1: Table S1.