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.

Now What?

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. Continue reading →

Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent for Benton, Linn and Polk Counties

Many of our readers have been tracking this issue over the last several years through the articles on this site. But I imagine many of you are wondering what to expect next, or are being asked by friends and neighbors who are concerned about your trees or theirs. Or just wondering what is going on. What to say?

So, here is a synopsis of what I generally see going on, and the consequences. A bit risky to do, given the role of individual sites and specific conditions. But this is such a widespread phenomenon, it warrants some interpretation, even at the risk of over-generalizing. But I provide the antidote at the end: links to more detailed information.

It is hard to miss all the dead and dying trees in the area. I have been getting dozens of calls about them. So what is going on, and what is to blame? It seems time to revisit this sylvan whodunit: What is killing all these Willamette Valley trees?

Who is involved? Douglas-fir is by far the most frequent casualty, along with other conifers such as grand fir and some ponderosa pine. But trees of many sorts are being affected –

hardwoods as well as conifers, both native and non-native. Many of the usual suspects – different beetles and fungi- can be found at the scene too.

What is happening? Symptoms often include dying branches and dead tops, low growth and vigor, sparse crowns, what we have called the “Willamette Valley crud”. It is now often progressing to the death of the tree. This may be happening to individual trees or groups of trees. The younger trees are usually the first involved at a site, eventually joined by older trees.

Where is it happening? This is certainly a Valley-wide phenomenon. But within the Valley, we are seeing the most significant damage in certain situations more than others. Sites with seasonally wet, poorly drained soils, or sites with rocky or shallow soils, exposed south facing aspects tend to be most hard-hit. These are places that we think of as marginal sites for most conifer trees. Our conifers are well adapted to the area, but not every site. Continue reading →

Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent, Benton, Linn and Polk Counties.

Conifer trees around the Valley continue to show signs of severe drought and heat stress this year. This should not be news to many readers:  young dead trees are now a common sight throughout the Valley.  Also, I wrote about this problem in past Tree Topics blogs (See stories from  May and September 2015 for background) but have new updates for this season.

I think you can expect to continue seeing similar damage to Douglas-fir this year and that symptoms will continue to unfold as the season progresses. Some of the trees damaged late last year did not show that damage immediately. The damage did not become evident until the trees came out of dormancy and began to grow this spring.  Also, the various insect and disease organisms that take advantage of       weak and damaged trees are likely to continue with their business this year, causing new signs of drought damage to show up during the season.  Happily, those players like Douglas-fir cankers and twig weevils do not typically blow up and kill healthy trees.  This suggests things will look much like what we saw and described last year and is likely to continue to unfold this season and maybe longer, whatever weather we get.  “It is important to understand that the effects of drought damage do not go away suddenly when the rain starts again” cautions Christine Buhl, ODF Forest Entomologist “drought can impact the tree’s whole plumbing structure, and affect the growth and vigor of the tree for years.”

Continue reading →