What I learned leading a crew

How Trees Make Ideal Pollinator Habitats

At Tree Trust, we believe a tree is never just a tree. It’s a shady retreat, a natural air filter, a community connector, and – for Minnesota’s bees – it’s essential habitat. From leafy boulevards to pollen-packed canopies, every tree we plant adds far more than beauty to our urban forest. Trees bring cleaner air, cooler streets, stronger communities, and—believe it or not—better moods. But trees also play a quieter, crucial role in supporting one of nature’s hardest-working and most at-risk pollinators: bees. Thanks to research from the University of Minnesota Bee Lab and the Minnesota Bee Atlas, a citizen science research project, we now understand more than ever how trees support wild bees across every stage of their lives, from food to nesting material to overwintering shelter.

Trees as Rest Stops for Bees

Minnesota is home to more than 500 species of native bees, and many of them depend on trees not just for food, but for safe places to live and rest. According to Thea Evans, Bee Atlas Project Coordinator and Researcher at the University of Minnesota, trees offer critical nesting sites, shelter, and overwintering habitats for many kinds of bees.

For example, leafcutter and mason bees often nest in natural cavities such as old beetle burrows in fallen logs. These above-ground nesters are also the most common users of “bee hotels,” which mimic these kinds of conditions. Tree Trust’s Summer Youth Employment Program crews even learned how to construct bee hotels (see image) using materials found on their job sites!

Even the fallen leaves beneath trees matter. Bumblebee queens overwinter under layers of leaf litter, while many ground-nesting bees use the soil beneath trees to raise their young. That same layer of leaves also supports butterflies, moths, and other beneficial insects through their life cycles. In short, when we let nature do its thing, it quietly supports a wide web of biodiversity (MNSTAC Webinar, 2025).

Leaves, Resin, and Bee Architecture

Trees don’t just provide shelter; they supply the raw materials bees need to build their nests. Findings from the Minnesota Bee Atlas reveal that many bees collect nest-building materials directly from trees:
  • Leafcutter bees trim neat, circular pieces from tree leaves, especially oak, ash, maple, redbud and hop hornbeam, to line their nesting spaces.
  • Resin bees collect sticky resin from trees to line and seal their nests.

These materials serve a purpose: tree resin helps protect developing bee larvae from moisture and microbes. In fact, honeybees use resin to make propolis, a glue-like mixture of tree resin, beeswax, and saliva that seals cracks in the hive and provides antimicrobial protection (University of Minnesota Bee Lab).

Top 5 Tips for Supporting Minnesota’s Bees Through Trees

Whether you’re caring for your backyard or stewarding a community green space, these five tips can help you create bee-friendly tree habitat year-round.
  1. Leave dead wood (logs or snags) when safe. They provide critical nesting habitat. Many bees nest in pre-existing holes in dead trees or logs. When safe to do so, leaving standing snags or fallen branches can offer much-needed habitat for cavity-nesters like mason bees (Osmia spp.). These overlooked habitats are essential to the life cycles of many native pollinators (Minnesota Bee Atlas, UMN Extension).
  2. Skip the fall cleanup. Fallen leaves insulate overwintering bees and butterflies. Those leaves on the ground? They’re vital winter shelter. Leaf litter helps insulate overwintering bees and other pollinators, many of whom nest at the base of trees or in shallow ground. Holding off on cleanup until spring gives them a better chance of survival (Minnesota Bee Atlas, UMN Extension).
  3. Keep the mulch ring three feet from the base of mature trees. Roughly 70% of native bee species nest in the ground. Keeping the mulch ring away from the trunk of the tree keeps the tree healthy and allows access for nesting bees (Minnesota Bee Atlas, UMN Extension).
  4. Plant a diverse mix of flowering trees to support pollinators. Early blooming trees provide essential nectar and pollen for bees emerging in spring, before most flowers appear. To support resilient urban forests, we recommend planting species like basswood, catalpa, yellowwood, downy hawthorn, and serviceberry. These trees feed pollinators early in the season and add diversity to the urban canopy. Planting a variety of trees and shrubs that bloom at different times ensures a continuous food source for pollinators throughout the growing season (Minnesota Bee Atlas, UMN Extension).
  5. Don’t overlook wind-pollinated trees like oak and birch. They may not offer nectar, but their pollen is an important source of food for many bees. While we usually think of nectar-rich blooms, wind-pollinated trees like oak and birch still matter to bees. Their pollen is packed with protein and is a critical food source for bees in early spring (MNSTAC Webinar featuring Thea Evans, 2025).

Trees for Bees: Grow a Thriving Minnesota

Every tree you care for or plant supports pollinators. By understanding the full role trees play in the life cycle of bees, from food to nesting to overwintering, we can make simple choices that support the health of bees, butterflies, and the ecosystems that help our Minnesota landscape thrive.

At Tree Trust, we’re proud to plant trees with purpose, and we invite you to join us in making Minnesota’s urban forests into thriving, bee-friendly homes. Stay tuned to our volunteer calendar for ways to help plant and distribute trees this fall.

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