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WSU/Pend Oreille Extension introduced the Sense of Place series in 1999, with a focus on local landscape and natural history of Pend Oreille County, Washington. A partnership with the Kalispel Tribe of Indians Natural Resources Department has allowed us to expand this program through EPA funding to include more classes, a newsletter and this website.

Cog and Wheel, Tooth and Claw

by John Stuart

Most interactions of the “tooth and claw” kind—the life sequences of tiny things—usually go unnoticed. Like the mites on our eyebrows, who cares about them as long as they quietly go about their business and don’t bother us. But the constant killing and eating of small creatures by bigger creatures is essential to the world we live in and it goes on at all levels.

Because insects have the ability to multiply their numbers to gargantuan proportions in a short time, nature has provided many different predators to control them. In our local forests, birds put a huge dent in bug populations, eating a large percentage of their own weight in food every day.

In the early 1990’s researchers at the U. S. Forest Service research station in La Grande, OR performed a unique experiment. They built PVC cages around 30 year old trees (30-40 feet tall) and draped them with material that left them open to insects but kept birds from reaching the trees. They were especially interested in spruce-budworms, which are a needle-eating or defoliating type of larvae. By comparing the caged trees with normal trees, they found that birds were eating five out of every six spruce-budworm larva. At least 27 different species of songbirds like Evening grosbeaks, Chipping sparrows, Swainson’s thrush and Western tanagers were lining up for dinner. They found a similar outcome for control of the larva of the Douglas fir tussock moth.

When we talk about forest insect outbreaks, we tend to focus on one particular “pest” at a time. But generally the story is more complicated. These insects are native to our forests and are usually present at low population levels, only killing the weakest trees. (The birds that regularly eat them don’t consider them a problem at all.)

But occasionally environmental factors like repeated periods of drought, extensive storm damage, or overcrowded conditions cause stress to trees over a wide area, and then these endemic populations can become epidemic, spreading faster than a virus in a preschool. As a tree fights off one attacker, it has fewer resources to resist others, so there is a “piling on” effect. Although we may blame the most obvious organism for the tree’s death, a detailed autopsy usually reveals multiple factors from root rot to bark beetles, often compounded by a prior history of stress.

The length and severity of these pest outbreaks is related to the health of the birds and the other predators that control insect numbers. Ironically, these predators are only present if their food is present, so a healthy forest requires dead and dying trees to support the required variety of organisms. Alarge tree in the forest, though a single organism to our eyes, is there because of an intricate mixture and intermingling of different life forms. Whether we notice these interactions or not, they are basic to the resiliency of our forests. As Aldo Leopold advised about forest management over 50 years ago, “To keep every cog and wheel is the first precaution of intelligent tinkering.”

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