For the Birds Radio Program: Aspen Tree

Original Air Date: April 22, 1996

Today Laura Erickson talks about a tree that gets better the older it grows. (3:38) Date verified.

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Every spring, the first place I look for migrants is my good old aspen tree, where I keep my scope trained when I’m around the house. This year, the first day the buds popped open, the first Yellow-bellied Sapsucker and Yellow-rumped Warblers of spring showed up right in its welcoming branches, alongside the last redpolls of winter. I can already predict that the first kinglets and hummingbirds to arrive in my yard will be there, too.

Aspens are vitally important in the northwoods ecosystem. They’ re generally the first new growth to appear after a forest is destroyed by fire or storm damage. In winter their buds feed grouse, and the first spring birds to migrate in depend on their generous bounty of sap, made accessible thanks to the little sapsucker. Because young aspen growth is a major food source for deer and grouse, some people justify short rotation cycles in the northwoods as being beneficial to wildlife. But this kind of forest management is really only beneficial to edge species.

It’s older aspens that make the biggest contributions to wildlife. The soft wood of aspen is easily infiltrated by fungus, and by the time an aspen reaches 40 years or so, it’s bound to have many growths of bracket fungi—those little half circle mushrooms that I used to think looked like dinette tables for squirrels. As time goes by, fungus infiltrates the wood in larger segments, decaying and softening the inside, causing heart rot. This makes the pulp less valuable to the wood fiber industry, but much more valuable to Pileated Woodpeckers. For as heart rot proceeds, the outside of the tree remains sturdy and hard, keeping raccoons and bear paws out, but the inside gets soft and rotten, easy to scoop out a fine nesting chamber. A pair of pileateds generally make at least a couple of new holes every year—during the nesting season, the mother sleeps in her own room while dad sleeps with the eggs or babies, and the adults may use these same holes or even make a few others for winter roost holes. But every spring they build anew, leaving those old holes for flying squirrels, Wood Ducks, Saw-whet and Boreal Owls, and other critters who need shelter but can’t excavate their own holes. Steve Wilson, an authority on Boreal Owls, told me that the average age of aspens used as owl nest trees is about 85 years, and the youngest was about 55. And these sheltering old trees continue to provide a generous food supply for grouse and other creatures.

We humans need aspens for pulp and paper, and we take for granted that wherever we chop down a forest, new aspen growth will regenerate. But we also need owls and woodpeckers. Forest managers have to cut down aspens for human consumption—wise foresters protect some fine old aspens even as they remove others. We must ensure that there be no dearth of bountiful old trees to keep our northern forests alive with baby birds and song and love.