By Brad Withrow-Robinson, OSU Forestry and Natural Resources Extension – Benton, Linn and Polk Counties
Winter storms seem to inflict damage to trees and forests somewhere in the area most years. Winds, snow and ice can damage individual trees or entire forest stands- breaking out branches, snapping the main trunk or tipping over whole trees, leaving landowners with a mess and many unexpected decisions.
This winter has been an exception in the severity of the November 2014 ice storm that battered a swath of the interior Coast Range from the Kings Valley area south to Mary’s Peak (see previous article). This unusual event caused irregular and spotty damage reflecting fairly small differences in aspect and elevation. Many landowners are still surveying the damage and considering their need to salvage and wondering if they can thin the damage out while leaving a healthy stand. Damage is severe enough in some cases to be forcing the decision to clear cut and replant young stands rather than the early thinning they were due for.
By Brad Withrow-Robinson, OSU Forestry & Natural Resources Extension, Benton, Linn and Polk Counties
While most residents of the Willamette Valley and Cascades foothills experienced unseasonably cold temperature in mid November, residents and landowners in the central Coast Range endured a serious ice storm. This was not a region-wide storm, but sure packed a punch in certain areas, with some people saying the damage caused may be as bad as or worse than that caused by the infamous Columbus Day Storm. I have not heard of any additional damage from a freezing rain event on December 1.
The main area affected is centered around Blodgett and Burnt Woods, stretching north through Kings Valley into Polk County and south to the flanks of Marys Peak. The McDonald Forest was shut down for nearly a week due to falling ice, limbs and whole trees, closing roads throughout the research forest and creating hazards to workers and recreationists. Crews and equipment are working to reopen forest roads throughout the area. Continue reading →
“We’ve never left much on the ground in the way of dead wood…not during logging, but wind damaged, etc. Our thought has always been that these rotting logs increase the insects in the forest, both good and bad. Is this a valid concern and if so, where is the balance between bugs and wildlife?”
He raises a point worth exploring. While calling an insect “good” or “bad” is a matter of perspective, for the purposes of this discussion let’s assume that “bad” insects are those that cause economic or environmental damage, and “good” insects are those that don’t. The vast majority of insects that inhabit western Oregon forests fall into the “good” category…with a few notable exceptions.
One of these “bad” bugs that the e-mailer might have in mind is the Douglas-fir beetle. This time of year, the adult beetles are flying around in search of Douglas-fir trees where they lay their eggs underneath the bark. Their favorite targets are large diameter, freshly downed logs—or standing trees that are weakened from another cause (root disease, soil compaction, etc.). Through the summer and winter, the eggs hatch and the larvae grow as they tunnel around under the bark (this activity is what kills the tree). The following spring, they have become adult beetles, and they fly away in search of new homes. If they can’t find another weak tree or fresh log, they will go after a healthy tree.
reddish bark dust in bark crevices is a sign of the Douglas-fir beetle (Photo: Elizabeth Willhite, bugwood.org)
Healthy trees can withstand a low-level Douglas-fir beetle attack, and in normal circumstances there are rarely enough beetles around to cause concern. The problem arises when the beetle population builds up and lots of them infest a healthy tree at once. When does that happen? In situations where there is a lot of freshly downed or damaged wood on the ground for them to target initially – like after a winter windstorm.
Here’s a true story for illustration.
In fall 2009, a landowner in the Coast Range was hit hard by beetle kill to his otherwise healthy, 100+ year old forest. Why? Here’s how we think this may have played out.
The stand is adjacent to a sawmill.
The big windstorm of December 2007 created lots of blowdown along the coast, though this particular stand was too far inland to be damaged.
Some of the coastal blowdown was not salvaged until summer 2008…too late, because Douglas-fir beetles had already found them during the spring.
The salvaged logs were brought to the mill, along with the beetle larvae living under the bark.
Then, in late 2008 the recession hit and the mill curtailed operations. The logs sat in the deck…and the beetles matured.
In spring 2009, they emerged and flew off to the neighboring stand, where they attacked the healthy, mature trees.
It was a sad situation, especially since the landowner had to cut more trees to avert further beetle damage, and in a poor market.
So, back to the e-mailer’s question: does retaining snags and downed wood for wildlife create a forest health risk? The take-home messages are these:
Most insects are not forest health risks.
In western Oregon, the Douglas-fir beetle (the “baddest” dead wood-inhabiting insect) only thrives in FRESHLY dead or downed trees. Once the snag or downed wood has been dead for more than a year, it is no longer a target. Instead, it will become inhabited by the dozens of “good” bugs that feed wildlife.
There needs a LOT of this fresh down wood to pose a forest health risk – like after a storm. According to Oregon Department of Forestry, a good rule of thumb is that fewer than 3 FRESH down logs/acre does not present a hazard.
After a windstorm or other stand-damaging event, yes, prompt salvage is important in order to prevent a beetle infestation. But, when scattered trees gradually die in a stand from other causes, it is hard to imagine when this would create a risky situation with respect to bark beetles. And during harvest activities, you can be strategic about how much dead wood is left behind, and in what conditions.
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