Science Monday, July 2, 2012

Forests, wildfires change over decades

The degree of damage done to forests from wildfires has changed dramatically from earlier last century.

The cyclical wildfires that have burned in the Rocky Mountains for millennia used to look much different, Craig Allen, an ecologist with the U.S. Forest Service, said at a recent conference in Aspen.

By analyzing tree rings, researchers have found that historical fires were frequent but burned mainly underbrush and young trees, thinning and opening the forests.

Once large-scale grazing began eating away at the “surface fuels” in the early 1900s, however, the historical cycle ended, a situation that was formalized by new policies of fire suppression. The tree density of forests skyrocketed, Allen said.

When generally drier winters in the Southwest over the past two decades allowed those new, denser forests to catch fire, the fires that took place were more likely to jump from treetop to treetop rather than spreading on the ground.

These fires were much more likely to burn whole stands of trees rather than simply thinning out the underbrush, opening the door for new, different species to move in post-blaze instead of the regenerated forest that would have emerged a hundred years ago.

■  Even hardy, drought-resistant junipers and pinyon pines are not immune to drought and pine-beetle damage. A new study from Oregon State University forestry researchers found that those two factors are the biggest contributors to the death of an estimated 2.5 million acres of pinyon-juniper forest over the past 15 years.

The researchers noted that even though pinyon and juniper have expanded their range in some parts of the Southwest over the past century, in other places the one-two punch of drought and increased bark beetle activity is now reducing the range again, potentially turning forested areas to grasslands.

In recent decades, most of the tree mortality has been caused by the normally drought-resistant trees being weakened by drought and, rather than recovering afterward, bark beetles have been able to take advantage of the trees’ weakened state to damage and kill the trees.

In addition to providing habitat and other roles, pinyon and juniper also play a key role in preventing erosion of dusty desert soils. As trees have died — as much 90 percent of them in some places, according to the researchers — wind erosion has been able to increase.

The wind-blown dust is then deposited on mountain snowpack, including in the San Juans and on Grand Mesa, where it can cause snow to melt faster and eventually reduce the amount of water making its way into the Colorado River.

■ Though extreme fire risk this year means there should be little to no fireworks to see here this Fourth of July, the next time you do see fireworks, remember to thank the wonders of chemistry.

Inside fireworks are packets containing finely ground-up metals. Once the firework explodes, those powdered metals begin to oxidize and emit heat and light, according to Kansas State chemistry professor Stefan Bossmann.

That light is a different color depending on the metal: Red for powdered strontium and lithium, orange for calcium, yellow for sodium, green for barium, blue for copper, violet for potassium and rubidium, gold for charcoal and iron, and white for titanium, aluminum, beryllium and magnesium.


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