Did you know diverse woodlands provide wonderful habitats for native pollinators? We’re shedding some light on the overlooked giants of pollinator habitat and how woodlands can be managed with pollinators in mind.
Minnesota has over 500 species of native bees and thousands of pollinators including bees, moths, butterflies, ants, beetles, flies and birds. This diverse group needs many different types of plants to live and thrive.
Prairies are often thought of as pollinator havens, but woodlands with their downed wood, standing dead trees, huge leaf canopies and diversity of herbaceous plants and trees also provide important habitat for many life stages of Minnesota's pollinators.
Pollinator facts
- Native pollinators support plants that help build soils, filter water, and sequester carbon.
- 85% of the world's flowering plants and two-thirds of food crops require pollinators.
- Some species of flies can look like bees. You can tell them apart by counting their wings: bees have 2 sets of wings while flies have only 1 set.
- 25% of all birds need food produced from plants that need pollinators.
- All flowers need pollination to produce fruit but some are wind-pollinated; however, even wind-pollinated plants are often used by pollinators for food and shelter, even though they are not required for pollination.
- Honey bees are non-native and most are managed like livestock to produce honey and pollinate crops. They are often regulated like chickens in Minnesota ordinances.
- Some plants rely on native pollinators’ buzzing to shake the flower and release pollen.
- Native pollinators including mason and bumble bees are important fruit crop pollinators.
While developing our climate-ready woodlands information we researched how each tree and plant species on those lists benefits wildlife, including pollinators.
Early blooming trees and spring ephemerals can be critical as early spring food sources for many emerging pollinators. Insects will seek out the spring blooms of maples, hawthorns, dogwoods, cherries, willows, serviceberry, and eastern redbud. Insects pollinate spring ephemerals including trout lily, trillium, Dutchman’s breeches, violets, wild geranium, and wild ginger among many others.
We also researched tree and plant benefits for beetles, ants and flies. We know that beetles pollinate pipsissewa, Canadian mayflower and bluebead lily; ants pollinate common marsh marigold, leatherleaf and chokecherry; and flies (which often mimic bees) pollinate bog rosemary, wood anemone, skunk cabbage and creeping snowberry just to name a few of the many, many plants that benefit our diverse pollinators.
Just as trees and plants provide for pollinators, pollinators are good food sources for other woodland wildlife including birds, amphibians, mammals and other insects.
Woodland management for pollinators
Forests meet the full habitat requirements for many pollinators throughout their life stages, from eggs, caterpillars and grubs, to mature butterflies, moths, beetles and ants. Pollinators benefit from woodlands that have some open canopy, which provides more light to sun and fly in, and allows for more herbaceous flowering plants to thrive.
Pollinators also benefit from wood and brush piles as well as snags (standing dead trees) that create habitat for wood-boring beetles whose tunnels are used by cavity-nesting bees. Some pollinators will also nest in burrows created under brush piles by small mammals.
Because diverse woodlands are home to many species of trees and plants, plants will flower at different times, supplying a continuous source of nectar and pollen. Woody plants support 10 times more butterflies and moths than herbaceous plants. For example, Lepidoptera (winged insects that include butterflies and moths) use native woody plants for shelter, pupation and feeding.
There are many things woodland stewards can do to enhance pollinator habitat across the forest. A few important ones are preventing forest fragmentation, reducing troublesome deer herbivory, minimizing pesticide use, and avoiding over-harvesting of wild plants.
Good woodland stewardship, including invasive plant removal, thoughtful timber harvesting, and corridor management are also important.
Invasive plant removal
We know invasive plant removal is good woodland stewardship, but it is also important for pollinators. Research shows that 15 times more native Lepidopteran species use native woody plant species as larval hosts than non-native ornamental woody species.
In addition to being less useful, some invasive plants can actively harm native pollinator populations. Female monarchs will lay their eggs on black swallow-wort instead of their preferred milkweed, even though larvae cannot feed on these plants and soon die.
Invasive species control commonly uses pesticides, and timing basal bark or trunk injection treatments until after flowering can help limit non-target damage. Because some pollinators use invasive plants, it is important to replace invasives with native plants to ensure continued pollen sources.
Woodland edges
Many woodland owners or stewards have woodland edges throughout the property. Creating a gradual transition between habitat types, called feathering, can enhance bumblebee and butterfly abundance. Many folks also find feathered edges more aesthetically appealing and natural-looking than straight edges.
Timber harvesting
Timber harvests are often essential management tools for resilient woods. Creating small canopy gaps can increase herbaceous plant flowering and allow butterflies to sun themselves.
Timber harvesting is also a good time to improve the climate resilience of the forest by diversifying tree and plant species. Species diversity is critical for optimal pollinator habitat.
Log landings are areas where logs are piled before hauling off-site during a timber harvest. These woodland openings are often reseeded after logging is complete and some will have residual wood. To manage these areas for pollinators, reseed with native perennial wildflowers and allow loose bare ground to persist along the edges, as this can be valuable for ground nesting and mason bees. The wood piles can be used as habitat for overwintering pollinators, reptiles and amphibians.
Corridor management
Managed trails and roads that run through the woods can enhance pollinator habitat. If the corridor is wide enough for sun to enhance flowering herbaceous plants, they can provide nectar and pollen later in the season. If the corridors or road edges are shaded they may harbor spring ephemerals that are critical for early-season pollinators.
It may be helpful to think of mowing as a vegetation management tool to be deployed with care. For some plants, waiting until after they’ve flowered may be preferable. (For invasives, it’s important to make sure the mower does not spread propagating parts or seeds, though sadly this is common with wild parsnip.) Rough or high mowing can leave behind herbaceous stems that pollinators use for overwintering or nesting habitat.
Mowing information from the DNR offers this advice: “Roadsides that have not been mowed for three years have up to three times as many [bird] nests per acre as those mowed annually. Mowing every three years is sufficient to control brush. Mow grass high to leave cover over winter.” The DNR also recommends spot mowing or spraying for weed control.
Benefits for wildlife from bees to bears
The improvements you make to your woodland benefit more than just pollinators. Forests are incredibly valuable for many large wildlife including deer, turkey, bear, moose, elk, wolves, bobcats and more.
Recent work from the University of Minnesota’s Offal Wildlife Watching project shows that birds, who find food via sight, visit gut piles in deciduous forests most often, followed by prairies and then conifer forests.
Carnivores, who detect food by smell, arrive at gut piles later than birds and are more common in conifer forests, followed by deciduous forests and then prairies.
Another interesting tidbit: barred owls are common gut pile visitors, eating both the gut pile and the small mammals those piles attract.