OREGON STATE UNIVERSITY

Insect epidemics a natural path to forest health?

05/27/1997

CORVALLIS - It took decades to give "Smokey the Bear" a decent burial and bring badly-needed fire back into the forest ecosystem - and it might take even longer than that, experts say, to enhance the image of bugs.

Even in an age of enlightened forest management, it's tough to find the word "insect" used without "pest" attached right behind.

But a series of new studies at Oregon State University has concluded that a wide variety of insects can play major roles in forest ecology - many of which are positive - and the bugs should never be viewed as just a problem we wish would go away.

"Research has already shown that insects are a key in cycling nutrients, speeding decomposition and building soil fertility," said Tim Schowalter, an OSU professor of entomology. "It now appears they do far more than that."

It's becoming clear, Schowalter said, that major insect attacks are a powerful tool to shape the very species and structure of forests into one that's appropriate for the terrain and climate - and one that's sustainable.

"In Oregon we've viewed the major insect epidemics simply as disasters," Schowalter said. "In fact, those destructive outbreaks are having an effect that's roughly comparable to fire. In some ways they're doing the forest underthinning that fire would have done and we should have done."

It's not really that simple, Schowalter said, and his research doesn't suggest we should just turn forest management over to the spruce budworm or bark beetles. For one thing, they've left behind a huge fuel load of dead trees that has really set the stage for catastrophic, stand-replacement fires.

But if nothing else, the insects are a clear indicator of forest health.

"What they're telling us is that fire exclusion allowed a huge invasion of understory shrub and tree species that don't belong there," he said.

The insects have already taken the liberty of killing many of those plant species, Schowalter said. Now - if catastrophic fires don't first burn everything up - the insects would help create openings in the forest, improve water availability and give a major nutrient pulse to the surviving trees.

In other words, they could work in concert with fire to restore forest health to Eastern Oregon - some areas of which, Schowalter said, are already more fundamentally healthy than they have been in half a century.

In pioneering research, much of which was done at the H.J. Andrews Experimental Forest near Blue River, Ore., OSU scientists have learned the roles insects play in forest ecosystem processes. Manipulative studies have examined herbivore and detritivore effects on plant productivity.

Defoliating and sap-sucking insects affect nutrient turnover. Wood boring insects penetrate bark and provide access for decomposers and water, accelerating decomposition. Outbreaks can open holes in the forest canopy. The surviving trees get a nutrient burst to improve their growth and health.

"In one study done on younger trees we found that 20 percent defoliation, which is light to moderate, doubled the amount of water and nutrients available to the plants," Schowalter said.

In a normal forest ecosystem with a diversity of insects and the natural presence of fire, Schowalter said, tree species that are appropriate for that terrain grow and thrive. Inappropriate species are weeded out. If drought or wet cycles tend to push the ecosystem out of its usual balance, the insect attacks and fire help to bring it back.

"Something has to establish a balance between the available water, nutrients and the demands of plants," Schowalter said. "We finally came to realize that fire was a big part of that. Now we need to change our view of insects, because they too play a major role."

At this point, Schowalter said, some necessary concessions may have to be made to decades of fire exclusion and insect suppression. As a recent member of Governor Kitzhaber's task force to study Eastern Oregon forests, he agreed with recommendations for low-elevation salvage logging and more use of controlled fire to improve forest health.

"In eastern Oregon we simply have to clean out those forest understories and reduce tree density," Schowalter said. "The public has to accept fire, and they need to learn more about the role of insects in the ecosystem."

Depending on the situation those insect effects may be either positive or negative, he said. Sometimes the losses suffered by a few trees help to boost the health of the survivors. And often a major outbreak is an indicator of an imbalance in the ecosystem that the insect attack may help to address.

In healthy systems, Schowalter said, it appears there routinely are reservoirs of many insect species, and their predators - but fewer major epidemics.