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What to do about those drought-damaged trees?

TreeTopics - Wed, 09/07/2016 - 2:35pm

By Amy Grotta and Brad Withrow-Robinson, OSU Forestry & Natural Resources Extension

Group mortality of Douglas-fir in May 2015. Douglas-fir beetle was found in all these trees. Photo Kara Shaw

We have certainly experienced some significant drought conditions lately.  Stressed and dying trees are showing up all around the Willamette Valley, with concern that this could lead to beetle outbreaks and still more trees killed.  Is it time to throw in the towel, cut your losses (so to speak) and just salvage everything that is looking poorly?  Maybe, maybe not.  The decision needs to be considered carefully, weighing individual sites and stand conditions along with your objectives for your property.  Anybody considering a salvage harvest needs to look before they leap.

As we’ve discussed several times over the past few years, 2013-2015 were hard drought years and we continue to see the cumulative effects on our trees. Many trees, conifers in particular, have dead tops or have died outright.  Since drought symptoms typically take a season or two to be expressed, what showed up this year is a result of damage from 2015.  So far 2016 is proving to be a more normal year, though it remains to be seen how the fall and winter will play out.  If we continue to get decent rainfall then we should start to see new damage taper off, but it’s too early to tell.

Beetles are a concern and both Extension and ODF have been getting plenty of calls about this.   Yes, bark beetles have been more active in the Valley this year in drought-stressed stands.  We expect this since beetles make their living off of dying trees, and are often seen more as a symptom than a cause of problems.  Having drought stressed trees does not automatically mean bark beetles will come find them.  And there are several types of bark beetles, some more damaging than others.

Reddish frass in bark crevices is a sign of Douglas-fir beetle. Photo: B. Withrow-Robinson

That said, if you have trees that suffered partial damage a year or two ago, and then died completely this year, it is worth taking a closer look on these and surrounding live trees for signs and symptoms of bark beetles such as pitch streams, frass, and fading crowns on live trees. Fact sheets from the Oregon Department of Forestry on the Douglas-fir beetle and the fir engraver will help you.  If you see something of concern you can contact the ODF Forest Health experts or your OSU Extension Agent for help (for backyard trees, call a certified arborist).  Where there are significant numbers of beetles, landowners will be looking to sanitize their stands by removing infested trees before new adults emerge next spring.

This is where you want to exercise caution and be wary of door knockers.

Regrettably there is a history of shady operators approaching landowners telling them one story or another about their trees dying or markets disappearing and encouraging them to harvest trees “before it is too late”.  It is invariably tied to an offer to take care of the problem for them.  Unfortunately, the landscape is littered with stories of folks who have accepted those offers and sold off some timber they had not otherwise intended to sell, often for much less than it was worth.

We are aware of a number of small woodland owners in the Valley having received unsolicited offers to buy their timber as a way to mitigate drought damage. The “buyers” warn of all the trees damaged by drought being killed by beetles and being lost unless harvested, and encouraging people to sell and get some value before everything dies.

Unsolicited offers to buy timber are nothing new to small woodland owners, and we always advise to be wary of them.  But this seems like a time to be particularly cautious.

An unsolicited buyer offering to assess the health of your trees for you is a clear conflict of interest and a definite red flag.  One outcome could be the buyer exaggerating the potential for future loss, thereby convincing you to sell healthy trees you had no intention to log or to accept a lower price for the timber than you’d like (claiming that it’s “better than nothing”).  Have a third party help you evaluate damage and if you think you want to proceed with salvage or sanitation harvest, move ahead as recommended with any harvest and seek bids from different operators.

You should realize that nobody knows the fate of these trees with any certainty.  Drought conditions may be winding down, or may stick around for a while yet.   Both choices – wait and see or do some preemptive salvage – involve risks that you need weigh.  Don’t be driven by speculative claims about the trees dying, and do not panic.  One or two beetle-killed trees in a stand is not an uncommon event and not a certain epidemic in the making.  The decision to salvage needs to be well-timed and well-planned.  Starting the job and then not finishing before beetles emerge in spring, or not properly dealing with slash, can make matters worse instead of better.  Applying pheromone caps is another option to protect healthy trees if beetle-infested material cannot be removed in a timely manner.

So, suppose that you’ve done your homework and decide that salvaging drought-damaged or insect-damaged trees is in your best interest and meets your property objectives.  You still have some due diligence to take care of.  Get bids and ask the logger for references, go see his past jobs and talk with people who worked with him.  Contact ODF to find out if there are any past violations, or the Association of Oregon Loggers for information on their credentials.  Finally, insist on a written contract.  Consult these publications for more guidance: Small Scale Harvesting for Woodland Owners and Contracts for Woodland Owners.

A final note, landowners in Linn, Benton and Lane Counties can sign up receive Emergency Forest Restoration Funds to remove drought-killed trees through the Farm Services Agency.  More info here (scroll down).  Folks in the northern Valley counties can get in touch with their local FSA to check on the availability of funds.

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Categories: TreeTopics

Young Stand Thinning Strategies

TreeTopics - Fri, 08/05/2016 - 1:01pm

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

Continuing on the general theme of young stand management and especially the need for thinning, I’d like to look at strategies for thinning a young stand. Let’s start with some things to keep in mind about Young Stand Thinning or YST (also called precommercial thinning or PCT):

  • The idea of young stand thinning (YST) is to avoid harmful overcrowding later by removing excess trees early on.
  • The impact of thinning out a tree is very local. The overall stocking level (trees per acre) can be misleading. It is the spacing among immediate neighbors that counts.
  • The greatest benefit of YST is increased growing space rather than selection among trees. Creating more growing space to benefit as many leave trees as possible is the primary goal. Culling is secondary.
  • YST is key to achieving longer rotations and many non-timber objectives many family forest landowners desire.

As discussed previously , the common practice of planting Douglas-fir on a 10×10 grid gives about 440 trees per acre (tpa),  which is too many trees to carry to an initial thinning harvest.    We plant extra trees to allow for seedling losses in the establishment phase, but depending on survival, we will likely be well above our target for the initial thinning harvest (250-300tpa). So we need to remove  1/4 to 1/3 of the trees in a YST if trees are to reach a usable size  before they become overcrowded.  There are several approaches to that.

If we have a plantation with a regular and uniform planting pattern, a very simple and efficient approach to this is row removal. Removing every fourth row would reduce to 75% of original trees/planting spaces (reducing from 440 tpa  to 330 tpa) and removing every third row would reduce to 67% (from 440 tpa to  295 tpa).   Each is illustrated below.


This illustrates removing each fourth row. Each tree in the two rows adjacent to the row removed is given space on one side (a common thinning rule of thumb), but not on the third row, so not every tree benefits similarly. Still, this may be an adequate thinning if we saw moderate initial survival (75-85%) and do some additional thinning in the inner leave row.


In this illustration removing each third row, notice that every remaining tree is given space on one side, ensuring that every tree benefits similarly. This thinning ratio is well suited to stands with high planting survival, but might be overly aggressive in stands with more modest survival.

Besides the mechanical and intellectual ease of row thinning, it can have added benefits if you are a little late in doing the job, and having trouble getting the larger trees to fall to the ground. Felling a row gives room to fell trees into an open space.

Another systematic and only slightly less straight forward approach is to remove every third or fourth tree in a row.   That sound too easy?  By saying you will choose any one of every 3 or 4 trees in each row, you can do some limited selection and remove small or defective trees preferentially.  But don’t get carried away, stay focused on the main goal of removing one of each group of three or four trees, not culling.  That comes later.  When you come upon a gap with a missing tree (previously thinned by deer, voles or drought) you may count it as a removal and move on, or not, depending on you actual stocking, your target stocking, and how many trees you need to remove.  You can also take a couple rows at a time and consider the 3 or 4 spaces in each row as a group of 6 or 8 from which to choose your two trees to thin out.

In this illustration removing every third tree in a row, notice that it also creates a pretty uniform benefit to all trees. Each leave tree generally gets opened up on two sides (when removal is staggered row to row), benefiting every tree similarly.



This illustrates the two systematic thinning strategies (1/4 left, 1/3 right), the local effect of a thinning gap and how it allows a tree to retain more crown. The greatest benefit comes from releasing each tree on at least one side.

So there you have a few simple approaches that will allow you to expand the growing space and effectively redistribute resources among your leave trees through YST. Each can be done with a minimal amount of thought and debate.  There are other schemes that also work.  But the point is to choose an approach that makes sense to you, one that you can do consistently, effectively and efficiently.  The earlier you do it (maybe around age 10 in western Oregon) the more efficient and beneficial it will be.

Remember, the idea of YST is to make room for trees to grow without harmful competition until more can be removed in the first thinning harvest, which should then pay for itself. It is at that initial thinning harvest that you can make more complicated decisions about spacing and arrangement to reflect your long term goals for a stand, such as habitat diversity or timber quality.

Young stand thinning is not all that complicated, but it does seem hard for people to get done. If you have too many trees it is a very important step towards keeping you on track.  Without it, it is often harder to achieve many landowners’ goals, especially those relating to aesthetics or habitat diversity.



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Categories: TreeTopics

Shrubs for Wildlife – Oceanspray

TreeTopics - Thu, 07/14/2016 - 1:10pm

By Amy Grotta, OSU Forestry & Natural Resources Extension – Columbia, Washington & Yamhill Counties

If one of your land management goals is to provide wildlife habitat, you’ll want to consider keeping a mix of native shrub species on your property. Shrubs provide a host of services to wildlife, including shelter or cover, nesting space, and food from their twigs, leaves, flowers, and fruit. With thought given to species selection and location, retaining existing shrubs or planting them can benefit wildlife without compromising timber growth or forest operations. This is the third article in our Shrubs for Wildlife series (see others here and here). Each article highlights one species that benefits wildlife in northwest Oregon forests.

Species Name: Oceanspray (Holodiscus discolor)

Description: A medium to large shrub, with long arching stems and up to 15 feet tall. The leaves are 1 to 3 inches long, lobed with a central vein and arranged alternately on the stem (center photo). The tiny cream-colored flowers grow in dense clusters at the branch tips and are present in late spring to mid-summer (top photo). The dried flowers persist into wintertime. Oceanspray’s name comes from the appearance of these flower clusters.

Wildlife Value: Oceanspray is beneficial to songbirds who use the shrub for cover. The flower clusters attract bees and other pollinators. Looking closely at the blooming clusters, I found them teeming with tiny insects (bottom photo). Besides pollinating the shrubs, these insects are going to be somebody’s lunch – those songbirds, perhaps.

Management Considerations: A shade tolerant shrub, oceanspray is found in the understory of mixed hardwood forests and in gaps of mature, open conifer stands. When harvesting, consider carrying oceanspray over to the next rotation by designating shrubs to be protected during harvest. Retaining clumps of shrubs rather than dispersed will reduce competition with planted trees.

If you are interested in learning more about creating wildlife habitat on your property, check out these publications:

Family Forests and Wildlife: What You Need to Know from Woodland Fish and Wildlife; and

Wildlife in Managed Forests: Early Seral Associated Songbirds from Oregon Forest Resources Institute.


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Categories: TreeTopics

Matteson Forest Update

TreeTopics - Fri, 07/08/2016 - 1:59pm
Stephen Fitzgerald flagging a stake found on the presumed property line

By Stephen Fitzgerald, OSU Research Forests Director and Extension Silviculture Specialist, and Amy Grotta, OSU Extension Forestry & Natural Resources – Columbia, Washington & Yamhill Counties

Management activities are underway at the Rubie P. Matteson Demonstration Forest near Hagg Lake. As any new property owner can attest, the first year of property management entails a mix of addressing immediate needs and thinking about longer-term goals and plans.  This year, our activities are focused on mapping, inventory and rehabilitation as well as readying the property for public use. Below is a summary of recent and ongoing projects on the forest.

Tree blazes face in the direction of the property line.

Last summer, we began walking the property lines to look for and flag old survey markers and corners. We found some old stakes and traces of blazes on trees and re-marked them to assist future surveyors. We will be doing a property line survey (with new blazes) in 2016-17.

Last fall, roadside spraying occurred along the main road into the property to control invasive plants. Backpack site preparation spraying was also done in three areas totaling 11 acres that had been harvested prior to OSU ownership.

Tree planting crew at work in January 2016


These three harvest areas were replanted this winter as the reforestation success prior to OSU ownership was poor.

We hired OSU forestry student Corey Thompson to help with our forest inventory. Corey is from Clatskanie and has previously worked in his family’s logging business.  Corey designed an inventory grid and this spring and summer has been out at the forest establishing plot centers. Inventory data collection will follow.

A parking lot will be constructed this summer. The purpose is to provide parking for tours and classes and to keep vehicles in the parking area to avoid transporting invasive weed seed into and from the property. For the parking area we are making use of a small patch cut (harvested prior to OSU ownership) located just inside the main gate. The parking lot will include putting down fabric and rock.

OSU student Corey Thompson in the 30-year-old even aged stand. Thinning is needed here!

Looking ahead to 2017, we would like to do a cut-to-length thinning in the 30-year-old plantations which comprise about 1/3 of the property. We intend to demonstrate various spacings and thinning intensities in this area. We will be using the inventory data collected this year to help design our thinning prescriptions. We’ll share that plan as it comes together in a future blog.

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Shrubs for wildlife: Snowberry

TreeTopics - Fri, 06/24/2016 - 10:11am

By Brandy Saffell and Amy Grotta, OSU Forestry & Natural Resources Extension

Snowberry leaves and fruit in the fall. Photo: Pat Breen, OSU

If one of your land management goals is to provide wildlife habitat, you’ll want to consider keeping a mix of native shrub species on your property. Shrubs provide a host of services to wildlife, including shelter or cover, nesting space, and food from their twigs, leaves, flowers, and fruit. With thought given to species selection and location, retaining existing shrubs or planting them can benefit wildlife without compromising timber growth or forest operations. This is the second article in our Shrubs for Wildlife series (first is here). Each article will highlight one species that benefits wildlife in northwest Oregon forests.

Species Name: Common snowberry – Symphoricarpos albus

Description: Snowberry is a medium sized shrub, growing in thickets and up to six feet tall. The leaves are simple, opposite, deciduous, and variable in shape. They are generally oval but can be nearly round (3/4 – 2 1/2” long). The leaf edges vary from entire to shallowly lobed on the same plant and same stem. The flowers are small (1/4”), pink-white, bell-shaped, and found in clusters at the end of the branch. The round, white, waxy berries persist into the winter; they are non-edible to humans and toxic due to the saponin they contain. Twigs are opposite, slender, smooth, and yellow-brown.

Small pink blossoms are present this time of year. Photo: A. Grotta

Wildlife Value: Snowberry is useful to pollinators as a host and food plant. The flowers attract Anna’s and rufous hummingbirds, as well as various insects including bees. Several birds have been observed eating the berries, such as towhees, thrushes, robins, grosbeaks, and waxwings. Birds also use snowberry thickets for cover. In addition, the Vashti sphinx moth (Sphinx vashti) relies on it as a food plant in its larval stage.

Management Considerations: Following harvest, snowberry resprouts readily from belowground.  To ensure optimum survival and growth of planted trees, control snowberry where it is likely to overtop planted seedlings.  Consider retaining snowberry plants on the site where they are not in direct competition with seedlings.  For those who would like to actively enhance wildlife habitat by planting snowberry, it tolerates a variety of environments, and can be planted in coarse sand to fine-textured clay, full sun to dense understory, dry well-drained slops to moist stream banks, and low to high nutrient soils.  It also establishes readily and tolerates general neglect.

Plant habit and fruit in winter. Photos: Pat Breen, OSU

If you are interested in learning more about creating wildlife habitat on your property, check out the Woodland Fish and Wildlife website.



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Postcard from Scandinavia– Parting shots

TreeTopics - Thu, 06/16/2016 - 2:02pm

Brad Withrow-Robinson, OSU Forestry & Natural Resources Extension


Our final days of the tour included meetings with the local landowners’ cooperative in Telemark County and visits to two specialty sawmills.

The Tinnoset sawmill specializes in shaping large logs for traditional style log homes. Most are sold to builders, but they do some custom building on site too.

Nearly completed home on site. Harald explaining the building process.


Getting a closer look at construction details.










The Svenneby family sawmill has been working with leading architects and looking for less traditional uses of wood, including many exotic (USA) species. We lucked into a presentation by nationally acclaimed architect Einar Jarmund who talked about the expanding role and popularity of wood in both commercial and residential buildings in Norway and showed a number of projects done by his firm  ( ) using materials developed and delivered by the Svenneby mill.


Turid Svenneby discusses weathering of oiled oak siding with tour member Claude Rowley. The Svenneby mill and farm is yet another example of a multi generation, multi-enterprise business. Next to Kirk (ID) are Thorvald, Turid and Ole Svenneby.





We could not help but noticing how common and prominently wood was being used in Norway, and particularly as architectural and visual elements around Oslo.  Why does wood seem less used, less celebrated here?


A building on the Oslo waterfront area sided with wood prepared by the Svenneby mill. Another, renovated building on the waterfront.




Large wood laminated structural elements visible in the airport.


Smaller wood furnishing and finish elements abound in the airport














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A Postcard from Norway

TreeTopics - Tue, 06/14/2016 - 1:35am

Brad Withrow-Robinson. OSU Forestry & Natural Resources agent, Benton, Linn and Polk Counties.

In the fjord regions of Norway, both forestry and farming are limited to the area between the rock and the water.   The bottom of the valley is farmed, and the narrow toes of the valley walls are forested. Many communities were not connected by roads until the 1920s.  It is beautiful country, but it strikes me as a beautiful place to starve. It is not hard to see why so many people left for America in the late 19th Century.  Those who stayed looked for alternative sources of income to supplement farm incomes/earnings.

Looking up valley and seeing patches of spruce and pine on lower slopes of valley wall.


Local County Forester Rune K. discussing management of Spruce in the Valley.


Many of the family farm and forest owners in the Andalsness area of Romdal Conty are now “farming tourists” to one degree or another. Farmers in the Innfjorden valley now run a cooperative of about 60 rental cabins in their traditional summer pasture areas near the head of the valley. They are popular destinations in summer and winter for fishing, hiking and skiing.  The vacationers are not limited to the cooperatives land holding, since Scandinavian tradition and law allows open access for such activities across all lands.

Jacob Hagen explains the conversion of the traditional common summer grazing areas to cooperative recreation rentals. Traditional rustic cabins like this are mixed in with newer rustic cabins.




It is not an easy or lucrative place to grow and especially harvest and sell logs.


Watching a gravity (down hill) logging operation near Byrkjelo Norway A turn of small spruce logs arriving at the landing



County Forester Torkel (wearing Sgakit logging tower T-shirt) talks harvesting equipment with Columbia county landowner/logger KC Van Natta.


Wish you were here.






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Postcard from Scandinavia– Parting shots from Sweden

TreeTopics - Fri, 06/10/2016 - 9:35am

Brad Withrow-Robinson, OSU Forestry & Natural resources Extension.


One of our visits was to a cooperative forest jointly owned by about a dozen families from Bengtshedens village. The Mellanskog landowner cooperative also has a significant share of ownership.

We were greeted on arrival by two of the family owners with coffee and cinnamon rolls before touring the forest.


Mellanskog Forester Lars Eric explaining management practices such as regeneration, thinning and fertilization in a 100-year-old stand of Scotts pine.




We visited the Log Max factory in Grangarde, innovative producers of logging processing heads. Our group observing Log Max and Eco Log equipment in their native habitat of central Sweden.










Regeneration of pine with seed tree cuts is common in Sweden and Norway.



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Postcard from Dalarna County, no. 2

TreeTopics - Sat, 06/04/2016 - 1:39pm

Brad Withrow-Robinson, Forestry and Natural Resources Extension agent for Benton, Linn and Polk Counties.

Dalarna County was the seat of a very old and important copper and iron mining industry, an early source of wealth and power for Sweden.  We visted the Falun copper mine, active since the 10th century and a UNESCO world heritage site.

Preparing to head down into the Falun Copper mine.

Why is that part of our forestry tour?

Forest products were a critical part of early mining industry, which needed massive amounts of charcoal and round wood to extract and process the metals. Forestlands near the mine were hard pressed to provide these products.  The mine is also the birthplace of world’s oldest stock company, which eventually became large forest and paper corporation Stora Enso.

Over-exploitation of forest resources by the mid-16th century led to a series of perhaps the world’s oldest forest protection rules.  In 1607 King Charles IX issued a ban on logging and charcoal production within a one-mile radius of the Falun mine (using the old Swedish mile, about 7 English miles). It was named the “Peace Mile” in hopes it would reduce disputes over unregulated charcoal production.

However it was not until 1754 that the surveyor Johan Brandberg finished measuring 112 points around the circumference of a the circle, marking each with stones.

from: Marker stone number 112 in the Peace mile ring, marked with an arrow.

See old and new maps of the circle drawn by Brandberg at:







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Postcard from Sweden – Dalarna County

TreeTopics - Thu, 06/02/2016 - 1:56pm

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


A New Approach

Dalagård farm & forest retreat is a large working forest owned by Cecilia and Leif Öster. These first -generation landowners are developing an active silvo-trouism enterprise to diversify the farm’s income and promote its sustainability. Forest products and hunting leases are other significant income streams.

We enjoyed a wonderful Swedish Mid-Summer style lunch while enjoying the beautiful setting.


Leif explains alternative forest management practices used near the guest complex. This is aimed at balancing the guests aesthetic expectations of forests with broader forest production objectives.

Local trees on display in a small educational arboretum are described for visitors.















A Very Long Tradition

Just down the road from Dalagård, we were welcomed into the home of Karen Perers, an eleventh generation landowner of a small forest & farm property in Dalarna County.


Karin shared insights into how her family and farm has contributed to the community over the centuries delivering first charcoal and firewood and later pulpwood and sawlogs “The family and farm have been producing those wooden things  that the times ask for” across several centuries, she said. A recognized leader, Karin is director of the Board for Melanskog, the large regional landowner cooperative hosting many of our visits in the area.


Karin shows and discusses the first map of the property, along with a modern one, each containing very similar information.


Note year on map heading: 1749.





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Categories: TreeTopics

Postcard from Scandinavia – Stockholm

TreeTopics - Sun, 05/29/2016 - 9:23pm

Brad Withrow-Robinson, OSU Forestry & Natural Resources agent

Our group of 26 family woodland owners arrived in Sweden this week at the start of the Scandinavia Forestry Tour.

The tour is organized by the Oregon Woodlands Coop along with Washington County Woodlands Association and OSU Forestry &

Woodland owners visiting the Skansen historic museum in Stockholm Sweden

Natural Resources Extension.

The purpose of the tour is to look at forestry practices in this part of the world, meet fellow family forest landowners and focus particularly on the strong role of landowner cooperatives in both Sweden and Norway.

Most of our group is from Oregon, but we have people from four other US states, as well as South Africa rounding out the group.

This is my first electronic post card from the tour, where I will try to share some of the things we are seeing and learning here.


Old traditional buildings at Skansen Museum


View of Stockholm




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Categories: TreeTopics

Effects of drought continue in Valley

TreeTopics - Thu, 05/26/2016 - 11:30am

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.”

What we are beginning to see and anticipate may be different this year is more damage to stands rather than just individual trees, and damage to older and larger Douglas-fir trees than was typical last year. The drought is likely adding to and exacerbating other problems lurking out of view, so crowded stands, existing root disease and marginal sites (wet or shallow soils, southern aspects) can all be expected to contribute to the problem.

Unfortunately, this implies potential economic or forest health issues. Any merchantable tree lost to drought represents an economic loss if not salvaged.  But larger (>8” dbh) drought-damaged Doug-fir trees can also support growing populations of bark beetles, such as the Douglas-fir beetle.  Under the right conditions Doug-fir beetles’ numbers can increase to the point where they can overcome the defenses of healthier trees in the stand.  Drought stressed trees are not generally considered as good a nursery material as winter storm damaged trees  but can support a damaging increase of beetles if conditions are right.  I may need to write more on that later in the season.

We will also likely see drought stress issues in other conifer species. In our local Valley ponderosa pine, it is already causing some limited outbreaks of the California five-spine Ips, a tiny but destructive beetle.  With several generations a year, Ips can rapidly increase in numbers when trees are stressed and conditions favor the insect.  Also, the Ips is able to use much smaller wood (just three inches or more in diameter) than the Douglas-fir bark beetle mentioned above, so even a young planation can provide brood material for the beetle.  Sanitation of dead and dying trees as well as slash materials >3” is a very important control measure for Ips.  For more information on the Ips life cycle and management, see this 2014 article about Ips  or follow links to other resources provided below.

The Oregon Department of Forestry has a series of fact sheets on insects, disease, drought and slash management.  Several are currently being revised, so be sure to check back in July to see the updated versions.




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