Woodpeckers: Friends or Foes?

[This blog post has been provided by Bec Wolfe-Thomas, an administrator for the Garden Professors blog group on Facebook.]

Pileated woodpecker. Photo by Josh Laymon

Woodpeckers (Picidae) frequently get a bad rap from gardeners. It’s often their impression that the birds irreparably damage trees, but this is untrue. Most woodpeckers are insect eaters; they can hear insects under the bark and in the wood of trees. They then target their drilling with uncanny precision to get their meal. This removal of insect pests, such as emerald ash borer, benefits the tree.

Emerald ash borer larva. Photo by Pennsylvania Department of Conservation and Natural Resources.

And what about the feeding holes left in the tree? This is an exciting bit of tree physiology! Trees are able to compartmentalize or isolate the wounds. After the woodpecker has made a hole to retrieve the insects within, the tree starts compartmentalizing the wound. How long it takes for a tree to compartmentalize a wound and close it depends on species and climate factors.

Compartmentalization of decay in trees (CODIT). Photo from Wikimedia.

Below are photos of woodpecker holes in various states of compartmentalization, from freshly drilled to completely compartmentalized and closed holes. Woodpeckers help keep trees healthy by preventing large pest infestations. And while the small feeding holes might be an aesthetic concern to gardeners, they’re only temporary. They will eventually be compartmentalized and closed, and the tree will be healthier in the long run by having fewer pests.

This woodpecker hole is partially compartmentalized; you can see the edges are rounded, no longer rough. Photo by Bec Wolfe-Thomas.
This wound has fully compartmentalized and all that is left is a pucker on the trunk. Photo by Bec Wolfe-Thomas.

[Please note the larger holes excavated for nesting will compartmentalize but will not close over time.]

Published by

Linda Chalker-Scott

Dr. Linda Chalker-Scott has a Ph.D. in Horticulture from Oregon State University and is an ISA certified arborist and an ASCA consulting arborist. She is WSU’s Extension Urban Horticulturist and an Associate Professor in the Department of Horticulture, and holds two affiliate associate professor positions at University of Washington. She conducts research in applied plant and soil sciences, publishing the results in scientific articles and university Extension fact sheets. Linda also is the award-winning author of five books: the horticultural myth-busting The Informed Gardener (2008) and The Informed Gardener Blooms Again (2010) from the University of Washington Press and Sustainable Landscapes and Gardens: Good Science – Practical Application (2009) from GFG Publishing, Inc., and How Plants Work: The Science Behind the Amazing Things Plants Do from Timber Press (2015). Her latest effort is an update of Art Kruckeberg’s Gardening with Native Plants of the Pacific Northwest from UW Press (2019). In 2018 Linda was featured in a video series – The Science of Gardening – produced by The Great Courses. She also is one of the Garden Professors – a group of academic colleagues who educate and entertain through their blog and Facebook pages. Linda’s contribution to gardeners was recognized in 2017 by the Association for Garden Communicators as the first recipient of their Cynthia Westcott Scientific Writing Award. "The Garden Professors" Facebook page - www.facebook.com/TheGardenProfessors "The Garden Professors" Facebook group - www.facebook.com/groups/GardenProfessors Books: http://www.sustainablelandscapesandgardens.com

7 thoughts on “Woodpeckers: Friends or Foes?”

  1. What a nice set of images of callus forming! Thank you. But I am still hoping that you will do a piece on rock dust as a soil amendment. Some people seem to think that anything that contains crystals will help soil. Doesn’t make sense to me, and I get some pretty aggressive questions about it. There are some nice videos on YouTube made by a man who trialed some rock dusts in his garden with poor results, but I could use some help explaining this issue.

  2. Based on this article, I am more than happy to welcome pileated woodpeckers into my garden. Besides the good they do, they are such gorgeous birds to observe.

    What about their relatives, the yellow-bellied sapsuckers? Have they any redeeming qualities?

    1. Like many woodpeckers, they do eat insects. The “sap holes” they excavate are used by a wide variety of other creatures. Butterflies, moths, bees, wasps, and other insects will feed at them. Their presence attracts other predators.
      Hummingbirds and other birds enjoy the easy access to sap. Even squirrels will treat themselves to the sugary sap.

      Please keep in mind sapsuckers and all woodpeckers are protected species.

    2. Yes they do have their place and they do eat a lot of insects. While there are some birch species that tend to have some difficulties with over feeding most trees do not have a problem with sap sucker damage.

  3. I would like to clarify the terminology used. Compartmentalization refers to the establishment of chemical barriers to decay within the tree, such as is illustrated in the Wikimedia photo. The other photos illustrate closure of the holes with wound wood. Although the holes have closed, decay is still present and active within the cavity, and potentially will weaken the trunk to the point where it will break.

    1. I don’t think there’s any way to know whether decay is still present, and in fact I doubt it would be present in most cases. Comparmentalization happens relatively quickly, while wound wood deposition is slower.

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