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New Mexico State University

New Mexico State University

News Center

Killers on the Loose in New Mexico Forests

LAS CRUCES -- Armed with only maps and colored pencils, a forest entomologist tracks killers. Inside a high-wing plane above the forest canopy, he charts their paths of destruction.

The tracker is Bob Cain, with New Mexico State University's Cooperative Extension Service. The killers are bark beetles and Western spruce budworms.

Each year, Cain conducts aerial surveys of 1.6 million acres of the state's forest land. "We're in the air for about two weeks every July when color changes from insect damage are most apparent," he said.

From the paper maps, data is transferred to a computerized mapping system and provided to forestry districts, landowners and the U.S. Forest Service. "This archive of insect populations may help foresters identify areas where tree removal or insect treatment would be beneficial," Cain said.

Bark beetles have been at outbreak levels since 1990 on ponderosa pine in the Lincoln National Forest. "Smaller outbreaks have been observed in all of New Mexico's forested communities," he added.

Bark beetle larvae tunnel under bark and kill trees by feeding on the soft tissue. They also introduce a blue stain fungus that interrupts the flow of water and nutrients within the tree.

"As these insects move from tree to tree, they transmit the fungus," Cain said. "Eventually, the needles turn red and the trees die."

During the time lag between beetle infestation and tree mortality, trees remain green. "This can be an issue for homeowners buying trees from a nursery or foresters marking trees for removal," he said. Trees may appear healthy when they're not.

Cain said that past grazing, logging and fire suppression have caused forest overcrowding, with denser stands of smaller-diameter trees. "Some forest ecologists estimate that a tree must be at least 30 inches in diameter to provide long-term ecological benefits to the forest and its wildlife," he said. "Many of our trees aren't reaching that size." Crowding stresses trees, making them more vulnerable to insect attacks.

In addition to crowded conditions, tree species at unusual elevations are increasing. "We're seeing Douglas fir and white fir growing in lower elevations where before ponderosa pine predominated," he said. These trees are attractive to the Western spruce budworm.

"These moth larvae feed on buds and needles, causing defoliation," Cain said. "The severity of budworm damage has increased in the past 50 years, particularly in mountain communities near Taos, Angel Fire, Mora and Chama." Outbreaks are lasting longer and occurring at lower elevations.

Insects and diseases are natural components of New Mexico's forest ecosystems. Tree loss caused by these elements creates open areas that provide habitat for wildlife. But chronic diseases and insect outbreaks may be indicators of unhealthy forests, Cain said.

"As a society, we're are moving toward a more preservationist attitude, where we want to protect the current state of our forests, even though current conditions may not be ideal" he said.

There is no easy solution to the forest health problem. "The present conditions have developed over many decades," he said. "Likewise, any efforts to improve forest health will be long-term."