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Washington State University

Extension Forestry

WSU North Puget Sound Extension Forestry E-Newsletter – July 2018

Volume 11, No. 2
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In this issue:

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Forester’s Notes

If it seems like there’s been a marked increase in dead trees of late, it’s not just your imagination. We’ve seen increased tree mortality throughout western Washington over the past few years of record heat and drought, with many species being affected. Over the past few months, though, there has been a particularly pronounced uptick in noticeable decline and mortality that has gotten a lot of people’s attention, especially with western redcedar and western hemlock. I have never had so many people contacting me with concerns, and it is indeed concerning. Let me share with you briefly my understanding of the situation, and then I want to talk a bit about what our response should be.

Western Redcedar

The western redcedar mortality appears to be from cumulative drought stress. No evidence has been found of any biotic agents such as insects or diseases. Our trees are highly stressed from repeated summers of record heat and drought. Western redcedar has low drought tolerance and so this species has been particularly hard-hit. We are thinking that many of these trees actually died at the end of last summer when we hit a new record for days without rain. However, this was followed by a very wet fall, winter, and spring, so the trees, though dead, stayed green for a time. Once things began to heat up in May, the dead trees then rapidly dried out and turned brown such that now we can finally see the damage from last summer. This is why all these dead trees appeared so suddenly.

Western Hemlock

Western hemlock is another common native tree with poor drought tolerance. In fact, hemlock can’t really tolerate anything less than ideal except shade. Just like with western redcedar, we’re seeing a lot of mortality right now, and it has been increasing over the past couple years due to the cumulative drought stress.

Typically, drought stress is expressed as dead tops or individually dead branches in the canopy (called flagging). This is because the tree wasn’t able to get water to these extremities. So trees dying from the top down is a good indicator of water stress. One of the common patterns of decline that we’ve been seeing with hemlock, though, is that branches are dying from the bottom up. It was thought that this was might be a different type of drought response where the tree is shedding its less-productive foliage to minimize transpiration loss in dry conditions. This is what I’ve been telling everyone until new information came out recently.

The new information is that there is actually a new disease that appears to be causing hemlock defoliation. It’s a foliar fungal disease in the genus Rhizoctonia. Unfortunately, at this point we don’t know much about it. It is thought that it is associated with drought. It is also thought that it is associated with extremely wet conditions in fall, winter, and spring. I am speculating that it’s a two-fold issue. The trees are weakened in the summer by drought such that they have low resistance to pathogens. Combine that with record rainfall the rest of the year which creates ideal conditions for a fungal disease to flourish. I’m trying to get more information and confirm that I am thinking about this correctly.

This brings up an important issue, though, which is that it’s not just the summer droughts we’re dealing with. We have been swinging between opposite extremes of record drought and record rain. No, it doesn’t average out–rather, it’s double-trouble.

An article from DNR pathologist Amy Ramsey talks more about the Rhizoctonia issue, along with info about a potential issue with Douglas-fir that could be of concern too (as if you didn’t have enough to worry about).

How should we respond?

I think it is appropriate to be concerned, but not to panic. If you have a dead or dying tree that is posing a safety hazard, you should have it removed. You don’t have to remove it entirely and grind out the stump, though. You can keep the bottom 10-15 feet of some of these trees as short but functional snags for wildlife. For the trees that come down, if you don’t need the firewood you could leave a few log segments on the ground to provide habitat and soil building.

Wildlife habitat is the silver lining when it comes to dead trees. About 40% of our wildlife species rely on dead wood, both standing dead trees (snags) and downed logs. Ironically, trees can provide more life when they’re dead than when they’re alive. In today’s managed forests and manicured landscapes, though, dead wood is getting harder to come by.

Other than removing safety hazards, from a practical standpoint, there is not much to be done right now other than to monitor and stay abreast of the situation. Spraying pesticides, cutting down big swaths of trees, and things like that are neither necessary nor recommended. There doesn’t appear to be any need to “sanitize” an affected area or anything like that. There may end up being fungicides recommended to treat for Rhizoctonia, but these would likely be for things like Christmas trees or ornamental landscape trees—not large mature conifers or forested areas. If recommendations change as more is learned, I will of course let you know.

Should we try to take some sort of action anyway?

I think our expectations are often calibrated by our experience in horticultural environments. If the rose bush has aphids or black spots, we go to the big box store and find some sort of product to apply. Trees aren’t rose bushes, though, and things don’t really work like that in the woods. Pesticides, fertilizer spikes, etc. are usually not the answer. They can be a waste of money, introduce harmful chemicals into the environment, and do nothing to address the actual issue. This does not mean you won’t find products advertised for this type of purpose or “tree services” offering to come out and spray some sort of potion. There are a lot of sales to be made off of fear, ignorance, panic, a penchant for a miracle cures, and our strong desire to do something whether it’s warranted or not.

I certainly understand and appreciate the desire to do something. It’s hard to sit by and feel powerless while trees die around you. Losing trees changes the character of your property and those trees are probably not replaceable in your lifetime. That’s an impact to your quality of life that shouldn’t be dismissed, even if it does have positive benefits for wildlife. Unfortunately, once it’s obvious that something is really wrong with the tree, the course is probably set. Even if you knew sooner that something was wrong, chances are there would still be nothing practical to do about it.

There are cases where pesticides or repellents can be applied as a preventative measure to protect high-value trees from certain bark beetle attacks. The key word here is preventative, though—it is not a treatment for an existing problem. Furthermore, it does nothing to address the underlying issue that would attract bark beetles in the first place. Bark beetles in western Washington are primarily opportunistic and prefer to attack trees that have already been killed or seriously weakened by something else, such as root disease, drought, overcrowding, or some combination thereof. It’s these underlying issues that are the real problem.

In our current situation, I think the key underlying issue is drought, which is beyond our control. There are things that are under our control, though, when it comes to helping our forests be resilient in the face of drought. The “Focus On” article in this edition of the newsletter outlines those things. To give you a quick summary, there are three key things for drought resilience: choose appropriate species for the site, control density, and encourage species diversity. These are all long-term strategies, though, and not quick fixes. There is a fourth thing I also recommend, which is to learn to tolerate more dead trees on the landscape. Part of adapting to climate change is adapting our expectations.

The problem with unwarranted actions

Most people I talk to about dead and dying trees appreciate learning about what’s happening and why, are able to shift expectations, and even feel some relief that it wasn’t because they did something wrong. In some cases, though, the person is not able to break away from a preconceived notion about the situation. Case in point—I got a call once from someone who had misunderstood a news article, was convinced the trees were all dying because of killer snails, and nothing I said could dissuade from this. In another case, there was a person convinced that all the trees in the area were dying because of XYZ insect, and when I explained that the XYZ insect doesn’t live here, the person told me I should be less concerned about geography and more concerned about stopping the infestation. I found out later that what had been characterized as all the trees dying was actually one tree in someone’s yard that was suffering from poor cultural practices.

Even though my reasoning did not prevail in these cases, there was probably no harm that came of it. There have been cases, though, where I fear there was harm. For example, a couple years ago a person called me to ask what to do because trees of all species across the property were dying and that everyone had said it was some sort of horrible bug and that all the trees needed to be cut down and burned immediately. The person could not articulate who “everyone” was (or even understand who I was). I explained that insects are species-specific and that mortality across species indicates an environmental problem (e.g drought). I further explained that insects are not usually the underlying cause of tree problems in western Washington (see above), that the underlying issue should be identified before taking action, and that cutting down and burning all the trees on the property would probably not be an appropriate action regardless of what the issue turned out to be.

“So you have a degree in forestry and you’re telling me that what all these other people told me is incorrect?” the person asked. “Something like that,” I said. At this point the person accused me of deliberately wasting their time and hung up on me. I found this odd, as this person was the one who called me, it was their property that they were about to seriously damage, and why bother calling me in the first place if all these other mystery people had already given what must be the right answer?

Another situation I found troubling happened just recently. A person called to say a large hemlock on their property had died a while back and another one was on its way out. The symptoms of defoliation from the bottom up were exactly like the Rhizoctonia issue we are seeing. The person had an arborist come out to do a full assessment, which was wise as the trees posed a threat to the house. This is where things went sideways, though. The arborist told the person that it was most likely bark beetles and that someone should come out to spray the tree. I explained to the person four problems with this advice:

  1. There are no bark beetles that attack hemlocks.
  2. The pattern of damage is totally different from bark beetle damage (but is a perfect match for the foliar disease we are seeing).
  3. Even if there were beetles, they would probably not be the underlying issue.
  4. Even if there were hemlock-killing bark beetles that were primary agents, spraying the tree now would be pointless because they would already be there and the damage is done.

The person was desperate to do something, though, so the sprayers were called out.

To add insult to injury, the arborist also told the person that there was evidence of insect activity in the firewood they had just cut up from the hemlock that had already been dead for some time, and that they needed to get rid of the firewood immediately. I did not have the heart to tell the person that insect activity in a tree that is already dead is normal and expected. Dead trees become full of wood borers and such that come in post-mortem and start the process of breaking down the wood (i.e. nature’s recycling team), and these are not agents capable of harming live trees. In other words, this would be a complete waste of perfectly good firewood that I’m sure has been hauled away at this point. There are situations where beetles do kill trees and, if it’s really recent such that those tree-killing beetles haven’t left yet, you may indeed want to dispose of the dead wood (or at least de-bark it). This was not one of those situations.

In these last two examples, it is unfortunate that the person got conflicting advice. I recognize the bind it puts people in to have two professionals say totally opposite things. I now worry that when I refer someone to an arborist, which I often do, that they might not get correct information. For that matter, I worry that I might not be giving correct information. In the end, though, the advice that feeds our need to do something seems to prevail whether it is warranted or not.

I present these examples not to shame or poke fun at anyone. I am a bit reluctant to bring these examples up at all, because I don’t want you to get the impression that I will think poorly of someone who has a question or misunderstanding such that you would be hesitant to contact me about an issue. On the contrary, I don’t expect people to have an understanding of these things and I want people to ask questions and learn. I present these stories as cautionary tales to illustrate how fear and our tendency to always want to do something are powerful forces that don’t always lead us to the right place.

Fear and courage

When it comes to caring for forests, I don’t think we should ever make decisions from a place of fear or do something just for the sake of doing something. It is right that we should concern ourselves with things like forest health, wildfire risk, and invasive species, but we should make decisions from a place of education and proactive planning, not fear.

All of this makes me think of all the times and ways I have invested time, money, and effort into making things worse by pursuing inadvisable courses of action, despite the warnings against, because I just wanted to do something and somehow try to manipulate a situation. This has happened way more often than I would like to admit. Ultimately, it is a really good thing that we have strong desires to take concrete actions to solve problems and make things better. The key is knowing when to act and when to not. We face many problems that require action. Will we take it? When action is not called for, though, can we learn to be still? Either case requires courage.

Kevin W. Zobrist
Associate Professor, Extension Forestry
Washington State University
Serving the North Puget Sound Area

 

Tree Farmer of the Year Open House and Tour – Arlington This Saturday!

This year’s Washington Tree Farmer of the Year award was given to the New family, owners of Nourse Tree Farm near Arlington. This annual award, given by the Washington Tree Farm Program, recognizes the best examples of forest stewardship in the state. To celebrate and share with others what they are doing, the New family is hosting a public open house this coming Saturday, July 21st.

The News are graduates of our Forest Stewardship Coached Planning program, which helped them to develop a stewardship plan for their property. One of their big endeavors has been to work with the Snohomish Conservation District to restore 30 acres of fish habitat by planting trees and re-engineering the stream in an area where spawning salmon were ending up dying in a field. This has become a great case study example of a successful restoration project.
In addition to their restoration project, the News have plenty of other things to share about their 160-acre property. Join us on Saturday for a tour of the property and a chance to network with other landowners. There will be exhibit tables hosted by local agencies and organizations, including WSU Extension Forestry, the Snohomish Conservation District, the Washington Tree Farm Program, the Washington Farm Forestry Association, and others. Elected officials will also be there to learn more about the importance of good forest stewardship.

The open house will run from 10:00 a.m. to 3:00 p.m. Tours will be offered throughout the day, so you can show up any time. Nourse Tree Farm is located at 1130 Stanwood Bryant Rd, which is 1.5 miles east of I-5 exit 212 (Stanwood/Camano Island exit). The Everett Daily Herald had a front-page feature article on the New family and Nourse Tree Farm on Monday. You can also watch a really nice five-minute video about their farm which features beautiful footage of the property—it’s worth the watch!
 

San Juan Islands Forest Owners Field Day – Friday Harbor August 25th

People attending a forest owners field day session overlooking Puget Sound.
This year’s San Juan Islands Forest Owners Field Day will be at Thornbush Farm on San Juan Island near Friday Harbor. The Field Day will feature a dozen different outdoor workshops specifically for people with forested property in the San Juan Islands. The Field Day workshops will focus on island-specific forest stewardship issues using local experts. Learn about current San Juan forest health issues, fire protection, mushrooms, wildlife, Garry oak restoration, and much more. The Field Day will also feature exhibits by local agencies that assist owners of forested property.

The Field Day will be 8:45 a.m. to 3:30 p.m. Saturday August 25, 2018. Gates and exhibits open at 7:45 a.m. For those of you coming on the inter-island ferry arriving in Friday Harbor at 8:15, you’ll arrive at the site in plenty of time.

Thornbush Farm is approximately 15 minutes from the Friday Harbor ferry terminal at 236 Ellison Ln, Friday Harbor, WA. From Spring Street in Friday Harbor, continue on San Juan Valley Rd, turn left onto Wold Rd, turn left onto Alaska Pl, turn left onto Ellison Ln, go about 1/4 mile around the pond and park outside the gate.
Register before August 16th and save $20. For additional details, a complete list of workshops, and to register, visit the San Juan Islands Forest Owners Field Day Website.

 

Invasive Weed Field Practicum – Mount Vernon Sep.15th

Learn to fight back against damaging invasives

Is ivy pulling down your trees? Are blackberries taking over your newly planted trees? Do you have stubborn holly in your understory? Are dreaded species like knotweed and Scotch broom popping up on your property? Invasive weeds not only inhibit the growth of or even kill your trees, they cause significant ecological harm by taking over ecosystems, crowding out native species, degrading wildlife habitat, and increasing erosion. Controlling these noxious invaders is a challenging but essential task for landowners.

At this fourth and final installment of this weed control series, you will learn to identify and control some of the most common invasive weeds that cause economic and environmental damage in forests, including: holly, ivy, blackberries, knotweed, reed canary grass, butterfly bush, Scotch broom, and more. The practicum will cover chemical and a wide variety of non-chemical control options.

Field-based, hands-on learning

These practicums are completely field-based and centered on hands-on learning. After safety briefings, you will don protective gear (provided) to watch demonstrations and then do hands-on practicing of multiple control techniques, including hand-pulling, root digging, using a weed wrench, sheet mulching, foliar herbicides, cut stump treatments, and stem injection. You will learn about safe use of herbicides, including what products to use for specific weeds, where to get those products, how to read a label, proper safety equipment, avoiding environmental damage, pesticide laws, tank mixing, calibrating a sprayer for the proper application rate, and clean-up.

Take advantage of low registration costs

These programs have been partially funded by a one-time grant, allowing us to offer these with much lower registration fees than we will be able to in the future. Mount Vernon Invasive Weed Field Practicum Details and Registration.

This program is funded by the Washington State University Western Extension Risk Management Education Center, the USDA National Institute of Food and Agriculture (NIFA). This material is based upon work supported by USDA/NIFA under Award Number 2015-49200-24225.
Western Extension Risk Management Education Logo
USDA NIFA Logo

 

Fall 2018 Forest Stewardship Coached Planning – Arlington and Carnation

Coached Planning class standing in the woods with a Stewardship Forest sign

A forestry class for property owners

Is your forest a recognized Stewardship Forest? Do you have the sign and the matching hats? Do you want to know why people say this is the best course they’ve ever taken? Would you like to walk through your woods with new eyes and learn about everything that is going on in your forest? Join one of our 2018 Forest Stewardship Coached Planning courses this fall.

Coached Planning is our flagship program. This comprehensive, university-based forestry class will help you get the most out of your property. Whether you have just a few wooded acres or a larger forested tract, if you have trees on your property, this class is for you!

Topics covered

  • How do you know if your trees are healthy? What should you do if they aren’t?
  • What types of trees do you have? Does your forest look like a “mess”?
  • Are characteristics of your property attracting or repelling the wildlife you enjoy? What can you do if wildlife cause damage?
  • When should you worry about trees being hazards?
  • How do you know if your trees need to be thinned, and how do you go about it?
  • Are invasive and noxious weeds taking over your underbrush? What are the risks and what can you do about it?
  • What kind of soil do you have and how does that affect what grows?
  • What is the risk of wildfire on your property?

Save money, too

As part of this class we will “coach” you in the writing of your own simple forestry plan that may qualify you for property tax reductions or conservation cost-share grants.

Registration is open for both classes

Carnation – Wednesdays starting September 5th

This class was previously scheduled for Preston but had to be moved to accommodate facility repairs. This class sells out every year and is already filling up quickly. Register before August 18th and save $35. This class sells out every year and is already filling up quickly. Carnation Coached Planning Details and Registration.

Arlington – Tuesdays starting September 18th

Register before September 1st and save $30. Arlington Coached Planning Details and Registration.

Courses in other parts of the state

There will also be Coached Planning courses in:

 

Red Alder Management Workshop – Kent Sep. 29th

People standing in an alder stand

Alder needs to be managed differently

Red alder (Alnus rubra) is the most common native hardwood trees in western Washington. This moisture-loving tree is most common in riparian areas near streams and wetlands, where it contributes to high-quality habitat and clean water. Alder is also a valuable timber species that can fetch premium prices for specialty markets. Alder is short-lived, though, and older stands can quickly lose their value, stability, and ecological function, often degenerating into brush patches dominated by invasive species.

Red alder needs to be managed differently than conifer stands. It has different growth traits, site requirements, and spacing needs. Its short life-span means timing is important for harvesting or managing successful natural succession, and this requires advance planning.

Alder challenges and opportunities

This workshop will take a comprehensive look at the challenges and opportunities that alder presents to landowners. We will explore management options for different alder stand types, including young, dense thickets and older stands that are falling apart. We will talk about market opportunities for alder and how to recognize and grow high-quality trees. We will also talk about managing natural succession for property owners who don’t want to clear-cut the alder but also don’t want it to become a brush patch.

The workshop will feature classroom sessions in the morning taught by experts in alder ecology, silviculture, and marketing. An afternoon field trip will visit a site to see what a property owner is doing to help transition an overpopulated and weak alder stand to healthier, longer-term forest cover.

Save the Date!

The workshop will be on Saturday September 29, 2018 at Meridian Grange in Kent. Registration is not open yet but will be soon. Watch the Red Alder Management Workshop website for updates.

 

Ties to the Land Succession Planning – Enumclaw Nov. 3rd

Keep your family farm or forest in the family

Your land will outlive you. Who will care for it when you’re gone? Will it be a family legacy or a family squabble? Will it be kept intact and protected, or will it be divided up and sold off in pieces? Will it become a source of conflict between surviving family members? What is the long-term future that you want for your property?

Death and taxes are life’s two guarantees. The Ties to the Land succession planning workshop is a chance to consider both of those in the context of your land, family, and long-term goals. Succession planning is more fundamental than estate planning. This is the “human side of estate planning” that focuses on communication within families and working together to maintain family ties to the land from generation to generation. This workshop will help you better understand the key challenges facing families who own forest and farmland and how to address those challenges in a way that works for your family.

The workshop will be held from 9:00 a.m. to 3:00 p.m. at Thunder Mountain Middle School, 42018 264th Ave SE, Enumclaw, WA 98022.

The Ties to the Land Program

Ties to the Land is an award-winning curriculum developed by leading estate planning experts at Oregon State University Extension and the Austin Family Business Program. Working as a family, you will learn about legal, economic, and, most importantly, relational aspects of transferring forests and farms from one generation to the next. This workshop is a mix of DVD-based presentations and practical exercises to help your family develop techniques to address tough issues.

Register Now

A special funding opportunity is covering part of the cost of this class, allowing us to offer this with lower registration fees than usual. Pre-registration is required. The registration deadline is 5:00 p.m. October 31st. Enumclaw Ties to the Land Details and Registration.

There are also other Ties to the Land workshops being offered in other parts of the state. Visit the WSU Extension Forestry website for more information.

 

Focus On: Drought

Drought, or the more generic term water stress, has been a big issue for trees in our area, resulting in tree decline and mortality in forests, natural areas, and yards across the region. Starting in 2012, we have had a series of record-setting summers in terms of heat and days without rain. This is taking a cumulative toll on trees.

Water transport in trees

Trees have an amazing ability to transport water from their roots all the way up to their tops, which may be over 100 feet in the air. The dominant theory of how this is done is called transpiration pull. A large portion of the stem of a tree is called sapwood, and this is a big plumbing system through which water (sap) flows upward. The sapwood comprises many tiny “pipeline” pathways for water. Water flows into the tree roots through osmosis, flows up the sapwood, and makes its way into the leaves. The leaves have tiny pores called stomata that open up for gas exchange to occur as part of photosynthesis. The pores open up to take in carbon dioxide, and in the process oxygen and a little bit of water vapor are released. This process is called transpiration.

Water transport in trees takes advantage of the fact that water molecules are polarized, which gives them a slight attraction to one another (cohesion) and other objects (adhesion). Surface tension, the “skin” on top of water, is an example of cohesion, and the way that water goes up slightly on the edges of a glass measuring cup (creating a U shape) is an example of adhesion. As a leaf pore opens up, the water molecule next to it evaporates out. As it does, its cohesive nature “pulls” the water molecule next to it forward, which pulls the water molecule next to it, and so forth. There is a continuous chain of water molecules, called the water column, which runs from the leaves down to the roots. They are stuck together by cohesion, and they cling to the sides of the narrow pathways in the tree by adhesion. So as a tree transpires, water molecules are pulled up the tree, hence the term transpiration pull.

The “pulling” by evaporation from the leaves creates a negative pressure that draws new water from the soil into the roots to replenish the bottom of the water column. As long as there is adequate water to be drawn in, all is well. In drought conditions, though, there may not be any soil water available. As water continues to evaporate from leaf pores, especially on hot, dry days, the tension on the water column gets tighter and tighter because no new slack is coming in through the roots. Under extreme water stress, the water column breaks at some point in the stem, which is called a cavitation. This can result in an air bubble in the pipe, which is called an embolism. The chain of water molecules is now hydraulically disconnected between the roots and the leaves. If the tree is unable to repair the disconnect, that water pathway no longer functions.

Direct and indirect impacts of drought

Classic symptoms of water stress in trees are dead tops and dead individual branches. If there is a major failure in the collective water column, water can no longer flow beyond that point of failure. Everything above it dies, leaving the tree with a dead top (figure 1). It could be that the water pathway to a particular branch failed, in which case that branch dies. The entire tree may also die due to water stress.

Tree with a dead top

Figure 1: A tree with a dead top indicates drought damage

Water stress not only kills trees directly as described above but also indirectly by causing them to be susceptible to other agents. When trees don’t have enough resources (e.g. water), they become stressed. The tree has to prioritize how to use its inadequate resources since it can no longer maintain all functions. One of the first two things a tree gives up is diameter growth. You can look at core samples from older trees and see spots where the diameter growth rings were particularly small, which may indicate that those were drought years. The other thing it gives up first is insect and disease resistance. This leaves the tree more vulnerable to things like root disease and bark beetle attacks.

In western Washington, bark beetles are not usually an issue with healthy, vigorous trees, as healthy trees can defend themselves against beetles. Rather, westside beetles tend to opportunistic and take advantage of trees that either just died or are severely weakened by some other factor. Thus, you may find bark beetles in drought-stressed or drought-killed trees. The beetles are not the underlying issue, though. Rather, the tree suffered from water stress which attracted opportunistic insects looking for an easy meal.

Healthy trees can even hold their own against root disease in some cases, compartmentalizing decay and keeping the disease at bay. If that tree becomes water stressed, though, it can no longer fight the disease and is overcome. We often see “pulses” of mortality in root disease areas during drought years.

Here is a real case study from Snohomish County. I visited a landowner who had a bunch of recently-dead Douglas-fir trees. The first thing I noticed were white fungal conks all over the stems of the dead trees. Did this fungus kill the trees? Then I noticed pockets of insect frass in the bark crevices. I peeled back pieces of bark and found Douglas-fir beetles inside. Did the beetles kill the tree? Then I looked around the area and saw that it was in the middle of a laminated root rot pocket (figure 2). What happened was this: the trees in the area were suffering from root disease but were holding their own to some degree. There were a couple of drought summers that tipped the balance in the disease’s favor, causing them to die from root disease. As they were dying (or right after), they were colonized by opportunistic bark beetles. The beetles bring in a fungus with them called pouch fungus, which causes white, pouch-like fungal conks to emerge from the beetle holes.

Pouch fungus conks on a tree stem, the inside of a piece of bark showing beetle galleries and larva, and a group of trees declining from root disease.

Figure 2: Pouch fungus conks (left), bark beetle galleries and larva (center), and a group of trees declining from root disease (right).

Water stress can set a whole chain of events into motion, and the stress can be cumulative over time. Some trees that endured the first few drought years finally succumbed in subsequent drought years, and we will see that continue. The result is a significant uptick in tree decline and mortality. Some people are convinced that there is some sort of disease or insect epidemic that is wiping out trees left and right. Insects and diseases may indeed be involved, but they are not new or unusual. Rather, they are simply taking advantage of trees that are beginning to succumb to water stress.

Management recommendations

What is the solution? In some cases, there isn’t a good one. Some trees are going to continue to decline and die due to adverse summer weather, and there’s nothing we can do except let it play out. If these newly-formed snags do not pose a hazard, they will provide a huge benefit for wildlife. 40% of our wildlife species require dead wood (standing or down). If the dead tree is a hazard, removal does not have to be all-or-nothing. Leaving the bottom 10-15 feet as a short snag will still provide important wildlife benefits while minimizing any damage potential.

The number one defense against the direct and indirect impacts of water stress is to maintain tree vigor. There are three key things you can do to improve the vigor of your trees. The first is to make sure tree species are appropriately matched to their sites. Where we see the most mortality (direct and indirect) from water stress is on certain “droughty” soil types. These tend to be gravelly soils that are excessively well-drained such that they dry out quickly. Trees on these marginal soil types may do OK most of the time, but in drought conditions they quickly succumb. Planting species that are more drought tolerant may be needed for these soil types. Your local Extension or Conservation District office can help you select appropriate species if you have sites where tree survival is poor.
The second key thing is density management. When trees are too crowded, they compete for resources like water and become stressed. In drought conditions, this competition becomes acute. When there is a very limited amount of available water, the more trees there are, the less water each will get. The WSU Extension Forestry program has educational resources to help you assess whether or not your trees are too dense. The “Focus On” article in the March 2018 newsletter goes through some simple assessments you can do.

The third thing is to avoid grass near trees. Grass and trees are not a good mix. Grass robs trees of water, which may never penetrate the sod to reach the tree roots below. Grass also harbors voles, which are rodents that will chew, girdle, and kill young trees. Keep the area around trees grass-free beyond the dripline. In a landscaping setting, replacing the grass around the tree with a good mulch will help retain water and keep tree roots cool. Do not pile the mulch up against the tree, though. In a forest setting, the natural forest understory plants and duff layer are fine.

One other principle to keep in mind is diversity. By encouraging a diversity of tree species on your property, you end up with mixed levels of drought and other tolerances that allow you to hedge your bets against various conditions. You also hedge your bets against insect and disease issues that are host species specific.

 

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Kevin W. Zobrist
Associate Professor, Extension Forestry
Washington State University
600 128th St SE
Everett, WA 98208-6353
425-357-6017
kevin.zobrist@wsu.edu

The WSU North Puget Sound Extension Forestry program is made possible in part by funding from Island County, King County, King Conservation District, San Juan County, San Juan Islands Conservation District, Skagit County, Snohomish County Surface Water Management, and Whatcom County.

Extension programs and employment are available to all without discrimination. Evidence of noncompliance may be reported through your local Extension office. Reasonable accommodations for the events described above will be made for persons with disabilities and special needs who contact us at the address above at least 21 days prior to the event.

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Extension Forestry, 600 128th St SE Everett WA 98208, 425-357-6017, Contact Us
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