Grazing reduces bee abundance and diversity in saltmarshes by suppressing flowering of key plant species

Davidson, KE, Fowler, MS, Skov, MW, Forman, D, Alison, J, Botham, M, Beaumont, NJ and Griffin, JN 2020 Grazing reduces bee abundance and diversity in saltmarshes by suppressing flowering of key plant species. Agriculture, Ecosystems & Environment, 291. 106760. https://doi.org/10.1016/j.agee.2019.106760

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Abstract/Summary

Globaldeclinesinpollinatorpopulationsandassociatedservicesmakeitimperativetoidentifyandsensitively managevaluablehabitats.Coastalhabitatssuchassaltmarshescansupportextensivefloweringmeadows,but their importance for pollinators, and how this varies with land-use intensity, is poorly understood. We hypothesisedthatsaltmarshesprovideimportantbeeforaginghabitat,andthatlivestockgrazingeithersuppresses orenhancesitsvaluebyreducingtheabundance-orincreasingthediversity-offloweringplants.Totestthese hypotheses,wesurveyed11saltmarshesinWales(UK)undervaryinggrazingmanagement(long-termungrazed, extensively grazed, intensively grazed) over three summers and investigated causal pathways linking grazing intensitywithbeeabundanceanddiversityusingaseriesoflinearmixedmodels.Wealsocomparedobserved beeabundancesto11commonterrestrialhabitatsusingnationalsurveydata. Grazingreducedbeeabundanceandrichnessviareductionsintheflowercoverofthetwokeyfoodplants:sea asterTripoliumpannonicumandsealavenderLimoniumspp.Grazingalsoincreasedfloweringplantrichness,but the positive effects of flower richness did not compensate for the negative effects of reduced flower cover on bees. Bee abundances were approximately halved in extensively grazed marshes (relative to ungrazed) and halvedagaininintensivelygrazedmarshes.SaltmarshflowerswereprimarilyvisitedbyhoneybeesApismellifera andbumblebeesBombusspp.inmidandlatesummer.ComparedtootherbroadhabitattypesinWales,ungrazed saltmarshesrankedhighlyforhoneybeesandbumblebeesinJuly-August,butwererelativelyunimportantfor solitarybees.Intensivelygrazedsaltmarsheswereamongsttheleastvaluablehabitatsforallbeetypes. Underappropriategrazingmanagement,saltmarshesprovideavaluableandpreviouslyoverlookedforaging habitatforbees.Thestrongeffectsoflivestockgrazingidentifiedherearelikelytoextendgeographicallygiven that both livestock grazing and key grazing-sensitive plants are widespread in European saltmarshes. We recommend that long-term ungrazed saltmarshes are protected from grazing, and that grazing is maintained at extensive levels on grazed marshes. In this way, saltmarshes can provide forage for wild and managed bee populationsandsupportecosystemservices.

Item Type:	Publication - Article
Additional Keywords:	Apis, Bombus, Grassland Management, Livestock, Pollinators
Divisions:	Plymouth Marine Laboratory > Science Areas > Sea and Society
Depositing User:	S Hawkins
Date made live:	04 Jun 2020 16:50
Last Modified:	04 Jun 2020 16:50
URI:	https://plymsea.ac.uk/id/eprint/8961

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