Mortality and flowering of great basin perennial forbs after experimental burning: implications for wild bees

Authors: Cane, James; Love, Byron

Submitted to: Rangeland Ecology and Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2018
Publication Date: 12/7/2018
Citation: Cane, J.H., Love, B.G. 2018. Mortality and flowering of great basin perennial forbs after experimental burning: implications for wild bees. Rangeland Ecology and Management. 41(2):124-127. https://doi.org/10.1016/j.rama.2018.11.001.
DOI: https://doi.org/10.1016/j.rama.2018.11.001

Interpretive Summary: The fates of native bees after fire in sagebrush habitats are inextricably linked with the fates of their native floral hosts and vice versa. Where fire disrupts the supply of pollen and nectar, surviving bee species would either suffer diminished reproduction or disperse beyond the burn perimeter. In turn, a vacated local bee fauna jeopardizes sexual reproduction of their floral hosts in later years, particularly in the Great Basin, where the common perennial forbs typically benefit from or require pollinating bees. Evaluating the response of plants to wildfire is difficult given the variability of fire characteristics (flame height, rate of spread, resident time), as well as the growing conditions in natural populations (soil conditions, water, pest and weed pressure). In this study, six species of prevalent perennial wildflowers were evaluated for their tolerance to increasing fire intensities using a propane burn barrel. Five burn prescriptions of varying intensity and duration were applied to cultivated rows of Astragalus filipes, Dalea ornata, Eriogonum umbellatum, Lomatium dissectum, Sphaeralcea grossularifolia and Penstemon cyaneus. Overall differences in their fire sensitivities were maximal at peak fire severity, ranging from 80% survival (L. dissectum) to complete mortality (E. umbellatum and P. cyaneus). One species (A. filipes) survived well (85%), but then up to half of the survivors failed to flower the year after burning. The post-fire fates of these plant:pollinator interactions is seen to be a function of the bees’ nesting habitus, their floral host’s sensitivity to a given burn intensity (both in terms of survival and flowering), and the reproductive interdependence of bee and floral host (taxonomic specialists versus generalists).

Technical Abstract: The fates of native bee communities in the Great Basin sagebrush steppe are linked with the susceptibilities of their floral hosts to increasingly frequent wildfires. Post-fire survival and subsequent flowering of six prevalent perennial wildflowers representing five families was quantified across a range of realistic fire severities created using a calibrated propane burn barrel. Five burn prescriptions of varying intensity and duration were applied to cultivated rows of Astragalus filipes, Dalea ornata, Eriogonum umbellatum, Lomatium dissectum, Sphaeralcea grossularifolia and Penstemon cyaneus. Overall differences in their fire sensitivities were maximal at peak fire severity, ranging from 80% survival (L. dissectum) to complete mortality (E. umbellatum and P. cyaneus). Several species (e.g. A. filipes) survived well (85%) but then up to half of the 95 burn survivors failed to flower the year after burning. The post-fire fates of these plant:pollinator interactions is seen to be a function of the bees’ nesting habitus, their floral host’s sensitivity to a given burn intensity (both in terms of survival and flowering), and the reproductive interdependence of bee and floral host (taxonomic specialists versus generalists).