Willow is the New Oak

A chickadee zips overhead, landing deftly on the edge of its tiny nest. Three bald babies bounce up for a bite from the bug buffet in momma bird’s beak. Ma and pa chickadee will be very busy for the next few weeks of spring. Caterpillar hunting is an all-consuming career for chickadee parents. Over the course of about 16 days, the three baby chickadees will need to eat between 6,000 and 9,000 caterpillars in order to grow into fledgling birds.

I recently had the opportunity to sit down for an interview with New York Times bestselling author and professor of entomology, Doug Tallamy. His groundbreaking work has helped people across the country understand the importance of keystone species for ecosystems, and our ability to support those species through good landscaping practices.

Caterpillars, it turns out, are critical to the productivity and biodiversity of ecosystems. “No animal transfers more energy from plants than caterpillars”, Tallamy explains in his many online presentations and books. Caterpillars are more efficient at converting plant energy to food for birds and other animals than any other organism. Hungry, hungry caterpillars eat leaves all day, turning plant amino acids into proteins. Turtles, foxes, voles, mice, birds and even bears feast on caterpillars.

One researcher discovered a black bear eating tent caterpillars. The tough caterpillar skins made it through the bear’s digestive systems intact, making it possible to count how many caterpillars the 146-pound adult female bear was eating on a daily basis. She was devouring between 16,000 and 22,000 tent caterpillars per day—that’s 20-22 pounds!—during the height of tent caterpillar season.

Given Tallamy’s fondness for oaks because of their ability to support a highly diverse array of moths and butterflies who raise their baby caterpillars on various parts of the tree, I thought we’d have a conversation all about oaks. Turns out, willows are the big bug bonanza in Minnesota.  “Willows are your number one keystone species for supporting caterpillars in MN. They beat oaks where you live. Willows support 359 species of caterpillars, oaks support 317.” He adds, “The farther north you go, the more oaks drop out. But 317 is still a good number.”

Doug explained that even if we have a small landscape, we can still do a lot to help biodiversity. “If you only have room for one tree, plant a Minnesota native tree. Willows, oaks, birches, aspen, alders and cherries are all highly productive choices.”

Helping me see the importance of planting native perennials under our trees, Tallamy explained that “94% of caterpillars drop out of the oak tree and spend the next portion of their life cycle underground or in the leaf litter.” When we mow under trees, we compact the soil and remove the leaf litter, making it impossible for most caterpillars to complete their life cycle and reducing their overall numbers. “Native viburnum, native blackberry and raspberry and native dogwoods are all productive. We don’t have a vast number of shrubs that are highly productive. We just don’t, I can’t help that. What we have are canopy trees that are small until there’s a light gap. That’s the basis of our understory.”

Peachleaf willow will grow 35-50’ tall, as will black willow. Bebb’s willow is shorter, coming in at 10-20’ along with sandbar, shining, slender, prairie and pussy willow, which are all native shrub willows. We love a decorative weeping willow, though they are native to China so they won’t feed many MN native caterpillars which should be enough to bend us back toward one of the wonderful native willow species.

Willows love water, though there are varieties that do well in almost every type of garden soil Minnesota has to offer. Consult with your native nursery when choosing native willow trees or shrubs to make sure the variety you’re choosing is right for your soil and sun conditions.

When asked whether he thinks people would object to sharing their new willow, oak or birch trees with so many caterpillars, Tallamy replied, “The entire horticultural trade has been based on plants being decorations. You don’t want anything to eat your decoration, but we’re moving past that, and the public is getting it. If your leaves don’t have some holes in them, they’re not doing their job. You’ve just created a dead ecosystem and we can’t afford to do that anymore.” His suggestion for people worried about bugs making holes in their tree’s leaves? “We should practice the 10-step program. You take 10 steps back from your tree and all your insect problems disappear.”

Owner of Minnehaha Falls Landscaping, Russ Henry has guided and performed organic transition in hundreds of home landscapes and several schools, parks, condos and office landscapes. His practices are rooted in healthy soil, growing abundant and healthy landscapes without using any synthetic fertilizers, pesticides or herbicides.