Cattle Blamed For Fires Livestock Grazing Kills Grasses Vital To Forest Ecosystems

Environmentalists have injected a new argument into the grazing wars in the West: Cattle cause catastrophic forest fires.

Joy Belsky, staff ecologist for the Oregon Natural Desert Association, came to the conclusion after reviewing 82 academic papers dating back to 1923. Her article was published in the May issue of the journal Conservation Biology.

“What we’ve heard about for years now is that the forest health problem is due to suppression of fire and selective logging,” Belsky said. “However, there’s ample evidence in the scientific literature showing that the increased density of forests and increased health problems started 50 years before fire suppression was initiated. And the increased density of forests started when livestock grazing was introduced.”

The idea has been well accepted in the U.S. Forest Service that extinguishing all fires for the past 75 years or so and harvesting only the biggest trees have led to millions of acres of sick forests that are especially vulnerable to catastrophic fires.

Before pioneers came to the West, low-intensity fires moved regularly through the ponderosa pine forests of the high-desert country east of the Cascade Range. With their thick bark, the big ponderosa pines could survive the small fires. But the grand fir and Douglas fir that grew in their shade were regularly weeded out by the flames.

Putting out forest fires allowed the grand fir and Douglas fir to grow in thick stands that become infested with insects. When the trees die, the stands are veritable tinderboxes, fueling hot fires that kill even the big ponderosa pines. Recognizing the problem, the government is working to put fire back in the forest and thin out dense stands of fir.

Federal land managers have increasingly accepted the idea that too many cattle left for too long can cause severe damage to the riparian zones along the rivers, contributing to the demise of salmon runs. The roots of trees and brush prevent erosion and store water, and the shade they create keeps streams cool.

Belsky argues that grazing by cattle and sheep also removes the grasses that once carried low-intensity fires through the forests. By removing grasses that compete with tree seedlings for scarce water and nutrients, grazing also makes it possible for more seedlings to sprout.

“This scenario has been found throughout the West,” Belsky said. “We have examples from New Mexico all the way through Washington state.

“Range scientists were not looking at forests. Forest scientists were not looking at the grasslands. That’s why everybody was missing this connection, though there is an enormous number of papers.”

Tom Quigley, science team leader for the federal government’s Interior Columbia Basin Ecosystem Management project, agrees that grazing - by livestock as well as wildlife - has an impact on forests.

But Quigley feels that the over-grazing from the late 1800s to the early 1940s, when cattle were raised for their hides more than for beef, has been a bigger factor than grazing under modern constraints.

“Most of that high-density grazing has already been done away with,” Quigley said. “Many if not most of our forest environments are showing substantial recovery.”

Quigley thinks fire suppression and selective logging are still the leading causes of forests’ declining health.