Foresters have spent millions of dollars through the decades battling bugs that feast on trees, but a new report by an Oregon State University researcher concludes that it may be better for the forests to simply let the insects be.
Some trees respond to bug infestations by growing faster than they would otherwise, says the report published in the fall issue of Conservation Biology in Practice. Insects are also nature's way of weeding out forests. They reduce crowding and competition among trees so the survivors can better withstand fires and bug attacks in the long run.
"There is now evidence that in many cases forests are more healthy after an insect outbreak," said Timothy Schowalter, the report's lead author and interim head of entomology at OSU. "The traditional view still is that forest insects are destructive, but we need a revolution in this way of thinking."
Firefighting and spraying of native forest insects such as tussock moths or pine beetles have left many Western forests so jam-packed with trees that regions such as Eastern Oregon's Blue Mountains are primed for unusually severe fires or infestations, he said.
"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," Schowalter said.
1975 findings Such thinking is not entirely new. Two U.S. Forest Service scientists wrote in 1975 that caterpillar "grazing" of leaves harmed trees in some years but helped them in others. Caterpillars typically attacked sickly trees first, leaving healthier and more resilient trees to flourish.
But most forest managers have continued an "us against them" approach to pest control, Schowalter said. They consider insects "unconditionally threatening forces" and show little regard for the long-term good they can do, he said.
Indeed, the world of insect science -- entomology -- breaks into two camps: those, such as Schowalter, who argue for the longer view that bugs benefit forests over time, and others who think that managers must control bugs to protect forests.
Each camp overlaps slightly with the other. Both see insects as a natural force, but they differ over how freely that force should function.
"It's true, they are an integral part of forest ecosystems, but the ecosystems are very different from the way they used to be, in that there are millions of people living here now," said Darrell Ross, a forest entomologist at Oregon State. "The hands-off approach is not so viable in this day and age."
By controlling major insect outbreaks, he said, foresters can prevent huge die-offs of timber that could fuel severe wildfires.
Schowalter agrees that insects cannot always be left to their own devices. In flammable, overgrown forests, prescribed burning and thinning can work -- perhaps in concert with insects -- to reduce fire hazards near homes.
Bugs and profits Likewise, landowners planning to harvest trees in a few years cannot afford to let bugs chew up their profit margin. But if the owner does not plan to log the trees for a few decades, bugs may do little harm. A few trees may be lost to insects, he said, but in several years the remaining trees probably will make up for that.
Studies have found that the more needles tussock moths strip off a Douglas fir, for example, the faster the tree grows afterward, perhaps to compensate for the setback. Other studies showed that Western forests produced as much or more wood 10 to 15 years after mountain pine beetle outbreaks than they had before.
Such growth may rise from the complex interplay between insects and forests.
Insects do not simply gnaw on trees. They also drive decomposition that naturally enriches the soil while aerating the earth with their burrows, Schowalter's report says. They also provide food for key wildlife, carry seeds through the forest and pollinate plants in a way that controls where plants and trees grow.
In fact, bugs are often a signature of a healthy forest.
Instead of spraying bugs, Schowalter said, forest managers should try to re-create the diverse and open forests that insects themselves would normally help craft. That means thinning and breaking up dense, uniform forests that otherwise resemble an unending buffet for insects.
Susceptible forests The more diverse a forest and the more widely spaced its trees, the less prone it will be to insects and fire. Many insects will not spread as quickly through open stands common to the arid interior West. And if a stand holds a few different species of trees, it's more likely that some of the species will survive an insect outbreak.
"If we get forests back to a healthy state, we'd have to spend less money to control fires," Schowalter said. "We could also expect that insect outbreaks won't be as severe, so we will have less expense to deal with them."
|
If you have come to this page from an outside location click here to get back to mindfully.org |