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Serving small woodland owners and managers in the Willamette Valley and northwest Oregon
Updated: 43 min 36 sec ago
Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent, Benton, Linn and Polk Counties.
In a previous article , I wrote that many folks in NW Oregon are growing too many trees in young stands given some common family forest landowners’ objectives, including doing a commercial thinning when the trees are in their mid 20s. Since most people are hoping to do a commercial thinning on their way towards a variety of longer-term objectives and stand conditions, we need to focus on reaching that first commercial thinning in a timely manner and leaving the stand in a good condition to meet future objectives. Let’s begin by looking at what it takes to have a commercial thinning.
My contacts in the business around the mid-Valley tell me that while the first thinning should provide a mix of saw logs and chip logs, most of the surplus trees removed in the thinning need to produce a sawlog or two if you hope to break even or make a little money (a mix of around 2/3 saw logs and the remaining 1/3 chip logs is a rule of thumb used by some). Too many small logs and you are losing money. That sawlog will vary according to the mill it is headed to, but is generally 20 feet to 32 feet long with a 6 or 7 inch top. Smaller wood goes to chip and saw or pulp.
Roughly speaking, you need a stand with an average size of about 10 inches dbh (or bigger) to get this desired mix of products to have a profitable operation in recent market conditions ($475 to $500 per MBF).
So why are people having trouble achieving that? It has to do with how trees grow in stands. Let’s review nature’s rules:
- Bigger trees need to use more site resources (mainly light, water and nutrients) than little trees.
- The resources available on any given site are limited.
- As a group of trees grows, it reaches a point where there are not enough resources to go around and trees begin to compete, leading to winners and losers.
- Eventually some trees have to die (the losers) for others (the winners) to have room to grow.
What’s neat is that there is a regular and reliable pattern to this process which applies generally to all species (when growing in groups of similar age). There is a predictable maximum number of trees of a given size that can grow together in a group.
So it follows that there is a predictable maximum average size for any given number of trees growing together in a group, according to its species. As a group of trees grows towards its maximum size for that number (its spacing or density), it will pass through certain stages along the way. These stages (e.g. crown closure) or zones (e.g. self-thinning) all correspond to different and increasing levels of competition among the trees, each occurring a predictable point. See illustration below.
As covered before, the idea in spacing a young stand is to have the “right” number of well-distributed trees to allow them to grow until they are big enough to support a commercial thinning, and to be able to do it “on time”, before future opportunities are affected by overly-intense competition. This generally means aiming to thin the stand when it is in the Goldilocks zone (yellow or gold), and avoiding slipping into the self- thinning zone (red). Bad things happen in the red zone. Trees start dying, starved to death for want of resources by excessive competition among their neighbors. This is euphemistically called “self-thinning”. Self-thinning is an entirely natural process that gradually allows room for surviving trees to grow larger. But in the process live crowns get smaller, individual tree growth slows down and all the trees suffer. If allowed to proceed too far (approaching the brown zone), the stand becomes too weak and unstable to be thinned effectively. That leaves few options besides letting the stand grow (and self-thin) for another decade or so until it can be clear cut, then start over. This is not necessarily a bad decision, but not the outcome many family landowners are aiming for.
This relationship of predictable stages (commonly expressed as a ratio of the maximum) also gives us predictable average tree sizes at which different stages are reached. This lets us know if trees growing at any particular spacing will reach a given target, like the 10 inch average size needed for a commercial thinning, before becoming too crowded and stressed.
Let’s consider some young Douglas-fir stands.
Growing at the commonly planted spacing of 10×10 (about 440 tpa, the column on the right), trees will just be 6” (on average) when they enter the Goldilocks zone, and barely 8” when they are pushing up against the red zone. We saw why it is hard to have a profitable operation at that size. But delaying the thinning operation is unlikely to fix the situation, since we won’t have reached even a 10” average before approaching the brown zone. Generally many the trees we’d like to remove in an early thinning will be smaller than average. A delay for any reason at this spacing is likely a big step towards a short rotation.
Trees planted and growing at an 11×11 spacing (360 tpa) may do a little better, growing into the Goldilocks zone at an average size of about 6½”, and reaching the red zone at about 8½”. Still shy of the thinning target while avoiding intense stress, but it might work for some people.
So what about a still wider spacing? Trees growing at a 12×12 (300 tpa) spacing have a lot more room to grow before crowding and competition begins to undermine other management objectives. At a 12×12 spacing trees will be about 7½”, when they fully occupy the site and 10″ on average when they approach the self-thinning red zone. It is much easier to see a profitable thinning operation in this type of stand, and less temptation to delay and push beyond the upper end of the desired thinning window. But should life or market conditions mandate a delay, this spacing gives a bit more breathing room. Other advantages of this stocking level include an earlier (if small) cash flow to offset some establishment costs, fewer, larger trees to handle in the thinning harvest, and a residual stand of deep-crowned, wind firm, rapidly growing trees which provides the landowner a wider range of silvicultural options.
Oh oh, so what if you planted at 10×10? Watch for an article soon on the nearly-forgotten practice of pre-commercial thinning (PCT).
Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent, Benton, Linn and Polk Counties.
In my travels around the mid-Willamette Valley, I am seeing a lot of young conifer stands (generally Douglas-fir up to 20 something years old) with just too many trees. Why do I say there are too many trees?
I know many people in this part of western Oregon who are patiently waiting for their trees to grow, hoping to do a commercial thinning (meaning sell the harvested trees to make at least a small profit) when their stand is about 25 years old.
All too often it is not working out that way. Instead, as the stand approaches the target age they find that trees have already become too crowded, with too many small, slow growing trees in the stand. The trees are still too small to support a profitable thinning operation yet. To thin at that point is to do so at a cost, although it may be best for the woodland in the long-run. To delay the thinning and wait for the trees to grow enough to make the thinning operation profitable is appealing. It may avoid the short term expense but is likely to weaken the stand at a long-term cost of growth, stand stability and future options. It is a classic “pay now or pay later” situation.
In young stands, the idea is to have the “right” number of well-spaced trees to allow the trees in the stand to grow more or less unchecked until they are big enough to support a commercial thinning, and to do it “on time”, that is before future opportunities are affected by intense competition. This should leave the landowner with a healthy, stable and vigorously growing stand easily shaped to meet any of a wide range of long term objectives that family landowners commonly aim for. These common objectives (see related article about objectives) including habitat diversity, recreational opportunities as well as periodic income, are generally best met by growing trees in longer rotations (>45 yrs) and with multiple thinnings over time. So it is important to get off on the right foot.
Of course there are many nuances in choosing the right spacing for any stand, but I’m saying there is a lot less nuance in the decision leading up to the first commercial thinning of a young stand than there is in later thinning decisions. It is fairly simple. In a young stand, we want to have the right number of trees to support a timely commercial thinning while avoiding excessive competition. This will keep the most options open for the landowner in the future.
We’ll look at what that number might be in another article.
By Brad Withrow-Robinson, Forestry & Natural Resources Extension Agent, Benton, Linn and Polk Counties
Last month I spent a morning at OSU attending the annual science meeting of the Vegetation Management Research Cooperative (VMRC). It was well worth the time.
The VMRC’s mission includes conducting applied reforestation research of young plantations from seedling establishment through crown closure and, to promote reforestation success. The VMRC’s research has an emphasis on practical, operational vegetation control, and their research is broadly relevant and readily applied to the needs of family forest landowners, so I do try to keep up on their work.
Since many of the member groups do use herbicides in their forest management, their research frequently does involve herbicides. But the work is not generally about herbicides per se, but rather about understanding the nature of weed competition and how different degrees of competition and disturbance affect seedling growth and vegetation community dynamics. They are interested in knowing the influence of the timing of competition control efforts on survival and growth, how the length and timing control each affects growth and survival (“critical period threshold”), or the interaction of different seedling stock types and vegetation control methods affects seedling growth and vegetation community dynamics. Good stuff to know.
The meeting was also a chance to meet the VMRC’s new Director and Associate Director, Dr Carlos Gonzalez-Benecke and Max Wightman. They kicked things off with an excellent summary of the past decade’s research conducted around western Oregon and southwest Washington. They also did some broader synthesis of results to help lead the coop forward in another decade of work.
The VMRC currently has 14 members including forestry companies, state and federal agencies. It is one of 11 research coops at OSU’s College of Forestry (http://www.forestry.oregonstate.edu/research/research-cooperatives). Each conducts research and applies the results to solve problems, develop new products, support long-term field studies, and develop decision support tools. A CoF faculty member leads each cooperative and members work together to develop a mutually agreeable research program, pool dues payments to support the cooperative’s operating budget, and provide significant in-kind support to leverage dues payments.
You may have seen my earlier posting on the Swiss Needle Cast Cooperative , and can expect to hear more about the work of the VMRC, SNCC and some of our other research coops in the future.
The post Understanding vegetation in young plantations: It’s what they do appeared first on TreeTopics.