Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent for Benton, Linn and Polk Counties
In my previous post, I summarized what I think we know about this ecological whodunit. In this post, I look at what it might mean for landowners in the area.
We seem poised for another stressful summer. May 2018 has turned out to be one of the driest on record, and we are unlikely to catch up in June. Long term forecasts are for another warm dry summer. We will just have to wait and see how it unfolds. But whatever happens this summer, I think we can expect to continue to see more sick, dying and dead trees. There are several reasons for this.
First, many trees are already stressed or injured by the past hot drought events and are in a vulnerable condition. While not yet lost, this stress makes them less resistant and more susceptible to the insects and diseases that are lurking about. A mild summer, or several mild summers would help. But even then they will not recover immediately. Their earlier stress and injuries also hamper their ability to recover and rebuild their resistance, even under good conditions.
An analogy might be of me falling off a ladder. The injuries I suffered when I hit the ground continued to affect my health and recovery long after I stopped falling (it is harder to exercise with a broken leg). It will take a while to recover, even if I stay out of trouble. It will take longer (or could kill me) if I keep falling off the ladder. For the trees, each of these summers is like another fall from my ladder.
Second, some trees are already lost. It may not be obvious, and they may still have needles, but they have been mortally wounded or have already been attacked by insects and will not recover, however our summer turns out. It is just a matter of time before those losses become apparent.
In the long run, I anticipate that there will be a sorting out of trees by species and by site. Harsh, marginal sites will likely continue to lose Douglas-fir in this drought cycle, with the flat headed fir borer often involved.
Grand fir will likewise have a hard time on marginal sites. Unfortunately, most of the low elevation Valley foothills now seems to be marginal for grand fir which is being lost across our region to the fir engraver beetle, another coconspirator commonly associated with drought episodes. Woodpeckers often work on these trees, stripping the bark in their search for the beetle larvae.
So we can probably expect to continue to lose some trees from some areas, but not all trees from all areas of the Valley. While this is an uncommon event, it is probably not unprecedented. Looking around, we see lots of old trees that show signs of past drought stress, like missing branches and flat tops. Lots of tress will survive, even in less than ideal sites. You may notice that Oregon white oak is often thriving in areas where conifers are struggling. It makes sense to maintain any drought adapted trees you have such as oak, madrone, ponderosa pine and incense-cedar.
What can be done?
Many of the calls I get are not just asking what is wrong, but what can be done about it. People are interested in saving a sick tree, or concerned about some mysterious fungus or insect spreading to other trees.
Unfortunately, there is generally not much to do but wait. This is a landscape-wide event driven by a multi-year weather pattern interacting with the local geology and ecology. Yes, a little grief counselling is sometimes involved in these calls. People get attached to their trees, and it is hard to hear that there are forces beyond our control that are causing them to die.
People often ask if they need to cut and harvest, or burn the infected trees to prevent whatever is killing their trees from spreading. Such sanitation actions can be helpful, but are often difficult to do effectively, especially in times of drought. If trees are downed in a major windstorm, we know when the trees fell, when they would be attacked and so, a date by which the sanitation activity must be completed to prevent another generation of beetles from emerging. But in a drought stress situation, there is a gradual wave of attacks. It is difficult to know when an individual tree was attacked and so, the time by which tree should be removed to effectively prevent beetle propagation. Once the tree is dead, the beetles have long since left, so it is too late to stop the beetles there. Sickly trees are vexing since symptoms may not show up until it is nearly too late for action, making sanitation difficult.
Sanitation may also not be as effective as hope for. The world is generally full of beetles lurking around. If a tree becomes so stressed to be vulnerable to beetles, they are there to find it. Leaving one more beetle-killed tree will not generally condemn its neighbors to an attack.
The Oregon Department of Forestry has an excellent series of fact sheets and videos on insects, disease, pheromone repellants, drought and slash management. I’d encourage you to visit the site to investigate your situation more.