By Rebecca Ohlin
Cottonwood trees give honey bees something they cannot get from nectar: sticky bud resin. Bees carry it home to make propolis, the material that seals gaps and lines the walls of their nest. On a walk beside a river, notice where the old trees stand and where younger ones can take root. Both matter to the future of that habitat.
Cottonwood Tree Facts
- Look for sticky buds as leaves begin to open. Honey bees collect the resin and carry it home on their hind legs. Beekeepers sometimes call the resulting propolis “bee glue.”
- Cottonwoods can root from cuttings. Before planting one, check which species belongs in your area and whether the site has room for a mature tree.
- Eastern cottonwood often grows along sunny riverbanks. Its tiny seeds need moisture and exposed soil to establish. You can read more about its habitat in the US Forest Service species guide.
In Minnesota, foragers often bring back resins from cottonwoods and balsam poplars. The University of Minnesota Bee Lab explains how a colony uses propolis to line the rough inside of its nest. This lining helps defend the colony against some microbes.
Wildlife that depend on cottonwood trees
- Cottonwood stands provide shade and shelter for wildlife and livestock. Deer and other browsers also feed on young twigs and leaves.
- Beavers cut branches for food and building material. Porcupines feed on the hanging flower clusters called catkins.
- The trees grow large enough to provide habitats for eagles, hawks, and other birds of prey to build nests along with smaller birds and woodpeckers.
- Warblers and vireos nest and feed in the trees. Listen from the river trail in spring when songbirds are calling from the canopy.
- Cottonwood leaves feed butterfly caterpillars. For example, NC State Extension lists eastern cottonwood as a host for viceroys and red-spotted purples. If you see a chewed leaf, look underneath for the caterpillar that used it.
- Several kinds of cottonwood trees grow across the United States. For example, plains cottonwood grows along rivers on the Great Plains. Black cottonwood grows in western North America. Their ranges and site needs differ.
- People have also made use of black cottonwood trees in the Pacific Northwest. A Washington guide to traditional plant uses describes how Indigenous communities used the sticky buds to waterproof baskets and boxes. It also records the spring harvest of the sweet inner bark.
Why young cottonwood trees need a river
Look for saplings beside the mature cottonwood trees on a riverbank. For example, when a spring flood recedes, it can leave behind the damp, exposed sand that tiny cottonwood seeds need. A stand full of tall trees may have few young ones if the river rarely exposes new ground.
Along the Missouri River below Garrison Dam in North Dakota, researchers compared 30 forest stands over nearly four decades. They found fewer young cottonwoods and more green ash. An old tree can still provide a nest site for birds or resin for bees. To keep that habitat for the next generation, the floodplain also needs places where seedlings can take hold. Read the US Geological Survey study of the Missouri River floodplain.
All that to say, to save the bees, we need to save the cottonwoods too. Please help spread the word?