FOREST INSECTS CAN BE PARTNERS, NOT PESTS

CORVALLIS, OR--The massive insect epidemics that have plagued

Pacific Northwest forests in recent years are mostly a reflection of

poor forest health conditions, overcrowding, overuse of chemicals,

fire suppression and introduction of single species tree plantations

or non-native species, a new report concludes.

Beyond that, these insect attacks are nature's mechanism to help

restore forest health on a long term basis and in many cases should

be allowed to run their course, argue Oregon State University

(OSU) scientists in a study published this week in the journal

"Conservation Biology In Practice."

Native insects work to thin trees, control crowding, reduce stress

and lessen competition for water and nutrients, the researchers

found. Some levels of insect herbivory, or plant eating, may even be

good for trees and forests, and in the long run produce as much or

more tree growth.

"There is now evidence that in many cases forests are more healthy

after an insect outbreak," said Tim Schowalter, an OSU professor of

entomology. "The traditional view still is that forest insects are

destructive, but we need a revolution in this way of thinking. The

fact is we will never resolve our problems with catastrophic fires or

insect epidemics until we restore forest health, and in this battle

insects may well be our ally, not our enemy."

Historically, Schowalter said, destructive forest insects such as the

Mountain Pine Beetle or Tussock Moth were native to Pacific

Northwest forests and served an essential role in keeping them

healthy. When trees became too crowded the insects would

eliminate weaker trees and reduce competition.

But because the beetles' reproductive pheromones only carried

effectively about 15 to 20 ft., naturally open stands of mature pines

were protected against widespread outbreaks.

In these same forests today, fire suppression has allowed shade

tolerant, fire intolerant species to crowd the understory, create an

entire forest stressed for water and nutrients, and beetles can skip

from one weak tree to another across entire stands.

The solution in cases such as this, Schowalter said, is to address the

fundamental issue of overcrowding through forest thinning,

controlled fire and insect attack, allowing the pine beetles to actually

help in the long term process of restoring forest health.

It now appears that insects are anything but destructive pests.

Rather, they are major architects of the plant world in both

structure and function, and in natural balance help to maintain

healthy and productive forest ecosystems.

According to the new report, insects influence their environments in

five key ways:

Insects aid decomposition, stimulate the breakdown of

organic materials, enhance soil fertility and plant growth,

burrow in soils and increase its porosity and water holding

capacity.

Insects that eat plants influence where their hosts can grow.

Sometimes they kill trees and other plants to reduce

competition, and many times feed on trees without killing

them in ways that actually improve the health and long term

growth of trees and forests.

Insects are a key food source for other animals, playing a

major role in the food chain.

Insects help disperse seeds, fungal spores, and even other

invertebrates from one place to another.

Insects are pollinators, and in this role also help control the

movement of plant species.

Through this multiplicity of roles, forest insects can help to control

plant succession, dictate which plants will be allowed to grow or

thrive in particular areas, and invigorate plant communities, the

report says.

Studies suggest that even when insects eat up to 40 or 50 percent of

foliage, they make little or no difference to plant growth and

survival. This type of moderate insect damage should not be

fought with costly controls, the researchers argue.

Wood production in western U.S. pine forests reached or exceeded

pre-attack levels about 10 to 15 years following Mountain Pine

Beetle outbreaks, research has shown, and the more an individual

Douglas Fir tree is defoliated by the Tussock Moth, the more it

compensates afterwards with increased growth, given sufficient

resources.

The insect outbreaks may alleviate drought stress by reducing a

tree's demand for water, and also encourage more competitive

interactions between plant species that ultimately work to the

benefit of the tree.

Insects may be so important to soil fertility that they may be a

better barometer of forest ecosystem health than the larger trees or

animals which live there, researchers say.

In natural forest communities, there are more than 200 species of

arthropods and more than 200,000 individuals in a square meter of

soil. The numbers of these arthropods can tell more than chemical

tests about soil concerns such as nutrient cycling.

In their natural role, insects are usually helpful to the forest and

rarely cause large epidemics, the research team reports.

"When you have a highly destructive insect epidemic, what that

really should be telling us is not that we have an insect problem, but

that we have a forest health problem," Schowalter said.

"It's monocultures and fire suppression that cause insects to become

nuisances. The pests that plague us are all too often of our own

making."

As these systems become more fully understood, Schowalter said,

it should be possible to work with insects, rather than against

them, to produce new solutions to maximize the yield of forest

commodities while achieving conservation goals and healthier

ecosystems.

"It's really simple on one level," Schowalter said. "We have to pay

more than lip service to the balance of nature." --ENS