How are tallgrass prairies managed? Grazing and Fire Page 1 of 13 - PDF document

12/3/2018 Butterflies, Bees, and Weeds: Improving habitat for pollinators through management of Minnesota’s tallgrass prairies Julia Leone , University of Minnesota, Conservation Biology Graduate Program Patrick Pennarola , University of Minnesota, Entomology Graduate Program Diane L. Larson , U.S. Geological Survey, Northern Prairie Wildlife Research Center Jen Larson , University of Minnesota Karen Oberhauser , University of Wisconsin, Madison Susan Galatowitsch , University of Minnesota Why do we care about butterflies, bees, and weeds? • Pollinators are in decline worldwide • Minnesota prairies are home to several imperiled bee and butterfly species • Weeds reduce native prairie plant diversity and make it less fit as habitat for beneficial insects and grassland birds How are tallgrass prairies managed? Grazing and Fire Page 1 of 13 Agenda Item: 08 1

12/3/2018 Why manage Minnesota’s tallgrass prairie? The wildfires and wide‐ranging herds of bison are no longer present John Metal Why manage Minnesota’s tallgrass prairie? Lacking fire and/or grazing, shrubs and trees would likely invade Ideal Management Outcome: Weeds Butterflies Bees Page 2 of 13 Agenda Item: 08 2

12/3/2018 Where did we survey? • 73 vegetation sites • Including 20 insect sites Data from MN DNR, US FWS; Jen Larson, 2016 Private citizen partners Butterflies Page 3 of 13 Agenda Item: 08 3

12/3/2018 How do butterflies depend on prairie habitat? • Nectar for adults • Larval host plants • Over‐wintering shelters How did we survey butterflies? Pollard transect walk: Observer walk: 30 – 120 min. What butterflies did we find? • All 5 families of Minnesota butterflies • 35 species at burned prairies • 40 BUTTERFLY SPECIES • 35 species at grazed prairies • 9 prairie associated species • 30 species were the same at • 1222 individuals burned and grazed prairies Page 4 of 13 Agenda Item: 08 4

12/3/2018 Individuals at burned sites: 789 Individuals at grazed sites: 473 Prairie Associated Species Fire and Grazing management are both important for butterflies • There are more butterflies at burned sites • There are more common species at burned sites • Many rarer species and prairie specialists are found at grazed sites Some butterflies were only found at grazed sites Graze‐only Broad‐winged Prairie Ringlet Skipper Silvery Checkerspot European Skipper Tawny‐edged Skipper Page 5 of 13 Agenda Item: 08 5

12/3/2018 and some butterflies were only found at burned sites Graze‐only Burn‐only Common Broad‐winged Reakirt's Blue Prairie Ringlet Skipper Checkered‐ Skipper Silvery Checkerspot Arogos Skipper European Edwards’ Skipper Acadian Tawny‐edged Hairstreak Skipper Hairstreak Regal Fritillary ( Speyeria idalia) David Wagner digginflowers Regals at burned sites: 31 Regals at grazed sites: 12 Page 6 of 13 Agenda Item: 08 6

12/3/2018 Bees Bees globally are facing threats from habitat loss, pesticide exposure, and pathogens How do bees depend on prairie habitat? • Adult bees feed on nectar, and provide larvae with pollen and nectar • Some bees nest in hollow stems • Many bees nest in soils Page 7 of 13 Agenda Item: 08 7

12/3/2018 Bee sampling methods: Bee bowls and meandering walk Bee sampling methods 5m 20m 180m 30 min – 120 min What bees did we find? • 121 bee species • 98 species at burned prairies • 30 bee genera • 94 species at grazed prairies B. auricomus B. fervidus • 12,540 individuals • 71 species were the same at burned and grazed prairies • 11 species of bumble bees B. bimaculatus B. griseocollis B. ternarius B. impatiens B. borealis B. pensylvanicus B. terricola B. vagans B. rufocinctus Bumble bee species occupancy Bumble bee species distribution 10 9 Species occupancy (no. sites) 8 Burned Species distribution (no. sites) 7 Grazed 6 5 4 3 2 1 0 Page 8 of 13 Agenda Item: 08 8

12/3/2018 Bumble bee species occupancy Bumble bee species distribution 10 9 Species occupancy (no. sites) 8 Burned Species distribution (no. sites) 7 Grazed 6 5 4 3 2 1 0 Grazing and fire are equivalent for bees • Slightly more bees were collected at grazed sites than burned sites (6,491 vs. 6,039) • Very similar numbers of species (94 vs. 98) • Most species occur in both managements • No significant difference , statistically, in abundance or richness between burned and grazed sites Beyond management: Other signals • Higher frequencies of flowers in prairies are significantly associated with greater numbers of bee species • Sandier soils are significantly associated with greater numbers of bees and numbers of bee species Page 9 of 13 Agenda Item: 08 9

12/3/2018 A subset of bees only found with one type or another Graze‐only Burn‐only Perdita Bombus Bombus Svastra perpallida rufocinctus rufocinctus obliqua Nomada Hylaeus articulata nelumbonis Colletes Bombus terricola Heriades Megachile susannae carinata mendica Plants Does management with fire result in a different plant community than management with grazing? • No! • Sites closer together on this graph had more similar vegetation Page 10 of 13 Agenda Item: 08 10

12/3/2018 Weeds: Soil moisture is more important than management type • Canada thistle Kentucky bluegrass Canada thistle and Reed 1.0 1.0 canarygrass prefer wet prairie 0.8 0.8 Mean frequency Mean frequency 0.6 0.6 • Kentucky bluegrass and Smooth 0.4 0.4 bromegrass prefer mesic prairie 0.2 0.2 0.0 0.0 • None showed a significant Burned Grazed Burned Grazed Mesic Smooth Bromegrass Reed canarygrass Wet preference for burned or grazed 1.0 1.0 prairies 0.8 0.8 Mean frequency Mean frequency 0.6 0.6 0.4 0.4 0.2 0.2 0.0 0.0 Burned Grazed Burned Grazed   Mean species richness Coefficient of Does prairie does not vary between Conservatism is a “quality” vary management types. measure of how  restricted species are to Average richness: between high quality remnant  24.39 in burned sites prairie (higher=more  24.47 in grazed sites management restricted)  Average Coefficient of types? Conservatism  4.06 in burned sites  3.70 in grazed sites We need both fire and grazing to improve habitat for prairie bees and butterflies Page 11 of 13 Agenda Item: 08 11

12/3/2018 Why do these results matter? <1% remains There is very little prairie left in Minnesota • Once 18 million acres • < 2% remains • Heavily fragmented How are we sharing this information? • Direct feedback to participating landowners and managers • Webinars • Workshop and field day for land managers • Public website • Public talks • Manuscripts in preparation Page 12 of 13 Agenda Item: 08 12

12/3/2018 Acknowledgements Botanists: Karin Jokela, Katie Schmidt, Larissa Mottl, Madison Rancour Insect field assistant: Grant Piepkorn Lab technician: Grace Haynes USFWS, Morris WMD: Sara Vacek MN DNR: Fred Harris, Robert Dana, Crystal Boyd, Nicole Gerjets, site managers The Nature Conservancy Private Landowners Sam Droege, USGS Thank you! Questions? Diane Larson: dlarson@usgs.gov Julia Leone: leone050@umn.edu Patrick Pennarola: penna041@umn.edu Page 13 of 13 Agenda Item: 08 13