In US 450,000 hectares of dead trees, what happened to them?

A few weeks ago, a group of officials from the United States Forest Service who were monitoring a Gigantic forest in the state of Oregon, in the western part of this country, found themselves faced with a scenario that caused them great concern.

Fatal factors

As announced by the Forest Service of that country, it is the greatest damage recorded in a single season since 1974, when they began to study the area.

Flying over the forests of the Fremont, Winema, Ochoco and Malheur National Forest regions, observers identified thousands of trees that ranged from red to orange, a sure sign that a tree is dead.

After completing the follow-up work, the researchers estimated that just over 445,154 hectares of forest with spruce, a tree that can reach 80 meters in height, were dead. As announced by the Forest Service of that country, it is the greatest damage recorded in a single season since 1974, when they began to study the area.

“When I looked at the situation and ran the numbers, the acreage impact was nearly double what we've documented so far,” said Danny DePinte, director of the US Forest Service's aerial inspection program.

In an interview that DePinte gave to the independent outlet Columbia Insight, the official launched some hypotheses that could have led to this record death of trees. The main ones point to drought and to insects and fungal diseases that act when the tree is weakened.

“When a drought hits, the whole forest weakens to the point that insects and diseases start working together, pushing the tree over the edge and causing it to die,” DePinte said, adding that more is needed studies to determine more precisely the causes of this event.

Towering volcanic domes

Oregon is known for its towering volcanic domes covered in a blanket of conifers that becomes sparse and fragmented on the eastern side of the Cascade Mountains before deepening into the high desert. The people who know trees best say there are many signs of trouble in Oregon.

“We are seeing forms of stress in all of our tree species,” said Christine Buhl, a forest entomologist with the Oregon Department of Forestry. "We just need to change our expectations of what tree species we can expect to be planted and where."

Researchers have been surveying the forests of the Pacific Northwest by air since 1947. Little has changed in the process during that time, according to Glenn Kohler, an entomologist with the Washington State Department of Natural Resources, which operates the program along with the Forest Service of the US and the Department of Oregon of Forestry.

Experts explain that if a tree encounters pests such as caterpillars and beetles, or if the roots of the tree are sick, it is still possible to heal itself, but the impact of natural disasters such as drought, wildfires, and storms is completely different, and healthy trees will also weaken their defences. Dying trees also harbour pests. The cause of the large-scale tree death in Oregon is unknown, but many people believe that drought is the culprit.

What species of firs were affected?

Firmageddon, as defined by the researchers, appears to be limited to so-called "true firs"; trees of the genus Abies.

The major timber crop of the Pacific Northwest, Douglas fir (Pseudotsuga menziesii), does not belong to the genus Abies and is not considered a true fir.

Mortalities were recorded for grand spruce, white spruce, spruce, noble spruce, and hybrid Shasta spruce. The highest mortality was observed at lower elevations where grand fir and white fir trees are abundant.
White fir was the most affected species, according to the survey data.

Aerial surveys last year documented nearly 230,000 acres of blistering heat in Oregon and Washington, DePinte said. Most of the damage occurred on slopes with south-facing aspects that absorb more sunlight due to the angle of the sun in the sky.

“It was the combination of the high temperatures in the afternoon with the sun going down,” said Chris Still, a professor in the Oregon State University College of Forestry. "We think a lot of those leaves were just cooked in place."

Increased risk of forest fires

Unsurprisingly, having more than half of the fir trees dead in some of these forests poses a huge fire risk. A dangerous fire period can occur within the first two years after a major die-off, DePinte says.

During these critical first two years, dead trees continue to cling to their dried needles in the forest canopy.

Figures from last year in Oregon show that average temperatures have risen about 2.2 degrees Fahrenheit since 1895, in part due to human activity, and that drought has worsened over the past two decades, with increasingly hot and drier summers and the threat of heat waves.

In addition, wildfires are more frequent and severe, and last year they burned a large number of trees in the interior west of the state. Scientists say that without climate change, heat waves of this magnitude would be nearly impossible.

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