Diameter Screens, Age Limits, Applied Science & Forest Management


Old-growth Douglas-fir and ponderosa pine, South Umpqua River headwaters, Douglas County, Oregon, April 19, 2010. Photo by B. Zybach.

Recent discussion on this blog has centered around the desirability of managing forest trees on the basis of their diameter, their age, or their basal area for a given location. Some of that discussion has included age classes of 150 and 300 years as points of departure. This photograph illustrates some of these concerns and was first published in an article on forest restoration I wrote last year and also posted to this blog: http://forestpolicypub.com/2012/04/04/8829/

This is a typical stand of trees in the upper South Umpqua River basin that I documented in a 2010 research study of 125,000 acres of forestland, mostly contained in the Umpqua National Forest. Our research focus was to determine forest conditions for the area for the ca. 1800 time period that preceded white contact in the basin. The larger old-growth trees are estimated to be more than 300 years of age, and the younger invasive conifers are in two basic age groups: the 30-inch to 40-inch second-growth trees are less than 150 years old, and the smaller understory and roadside poles are probably 20 to 40 years of age.

In 2009 there were two sizable stand-replacement crown fires in the study area: the Boze and the Rainbow fires, totaling about 15,000 acres between them. Prior to these two events, there was no evidence of any other crown fires of this magnitude at any other time since 1800; i.e., these types of fires were unprecedented during historical time. Other large-scale wildfires in the area, such as the 2002 Tiller Complex, were noticeably spotty and only crowned in certain locations — mostly younger plantations in that instance.

Several thousands of acres of this type of condition were found and documented in the study area. The old-growth stem count was about 5-15 trees per acre, while the invasives (I know Sharon doesn’t like this word, but I don’t know what else to call them in instances such as this) totaled about 100 stems or more an acre. These trees are having two deleterious effects on the old-growth that are being “preserved” for wildlife habitat (which was notably more present, diverse, and abundant in the remaining Indian prairies and meadows): 1) they were competing directly with the older trees for sunlight, water, and nutrients; and 2) they were making crown fires such as the Rainbow and Boze now possible. Either way, they pose a very powerful threat to the remaining old-growth in the landscape.

The decision to passively manage these trees has resulted in an increasing threat to the health and survival of the old-growth for the reasons just stated. Suddenly opening them up from competition increases the risk of windthrow due to lower stabilizing branches having been shaded out long ago. Many of the remaining old-growth have become top-heavy as a result. However, based on my observations of the past 50 years, if the competing vegetation were removed, the large majority of the remaining trees would survive and benefit almost immediately (“about 5 years”) by the removal of competition — and at a potentially good profit, with numerous rural jobs, useful products, and greatly improved wildlife habitat for many other wildlife species, including understory shrubs and forbs, ungulates, carnivores, birds, and insect pollinators.

To try and use an homogenized diameter screen or age limit in managing this stand would be a waste of time. I think the same is true for a basal area approach. Common sense states the obvious: use it or lose it. If some animal species prefer this type of situation, then they will have to contend with a diminishing resource because of the problems just stated. My thought is to actually preserve, via active management, as many of the remaining precontact trees and stands as possible.

Those are my experiences and opinions, though, and there has been little scientific research in regards to these situations. Other thoughts?


  1. Bob, I’m just curious here, but how would you respond in the case of two P-pines or even D firs close enough to affect the other, with one being precontact and the other being of similar size but with substantially more live branching? Let’s pretend for now they’re both healthy.

  2. Thanks, Dave: If they were in a meadow, prairie, or savannah, I’d leave them both. In the photo, for example, I’d leave both of the old-growth and about three “replacement” second growth, widely spaced around the perimeter of their driplines. Then I’d monitor the results and maybe make another entry with different considerations in ten or thirty years, unless disease, bugs, or windthrow became involved. You? (And I’m curious how Larry and Mac, the experienced tree markers, would handle this, in addition to other readers of this posting).

  3. How would I handle that hypothetical situation? Haven’t a clue since I’ve never marked a stick in the west and if I ever encountered a stand like the photo I’d fall down and worship. That said, my first job with the F.S. (1943) was helping mark an improvement cut, the initial cut in old-growth shortleaf on the Ouachita N.F. The appearance and condition of these stands were as close as you get in R-8 to old-growth east side ponderosa. The basic rule was to remove the trees that wouldn’t make it till the next entry – 20 years. Tree health was the sole criteria and I can quote the marking rules to this day. We weren’t allowed to do any thinning (don’t ask me why) and we weren’t concerned with basal area or diameter limit, or with saving old trees, scenic values, endangered species, protests, appeals or litigation. We were producing timber to support the troops.

    Those were simpler times with clear objectives, a much clearer vision of the future and a far different Forest Service. Little did we know.

  4. If I knew I could go back in 20 years? And 20 years again?
    But yeah, three nice “comers” or maybe four would stay for sure, that kindling on the left would definitely get mowed flush. On the far right, I’d leave the farthest one away from the huggee in that cluster, or maybe not depending on what’s going on in the crown.
    Up front, the best crown of those two stays.
    Of course, I’d be watching like a hawk for any bad signs of heart rot, ready to pounce. In that case, it would probably be fine to cut the fat end off and leave that lay as a shroom grower, take the sound wood higher up in for premium milling as finish wood/eye candy.

  5. Sounds good Dave. Hey Bob have you been to any of the show and tell at the Tiller Ranger District has been putting on about harvest in the Whiskey fire? Seems like the Ranger is trying. Of course Kwild is oppose to harvesting any large diameter trees. But then since in will be August at the soonest that the FS can offer anything for sale, it might be that ony the larger diameter trees will be marketable.

  6. Dave’s long-distance prescription echos the early marking rules for old-growth shortleaf in Arkansas. As we approached a tree we looked first at the crown: stag-headed? flat-topped? needles tufted- coloration? Then we looked at the bole: plated bark? lightning strikes? beetles? red-heart?. When we reached the tree we looked for root-sprung? butt rot? unsound fire scars? Then we put the info all together and either swung the axe and marked the stump with the “US” or a light triple-hack (tree evaluated and left) and moved on. The basics really don’t change.

  7. Appreciate the discussion gentlemen, as one who worked logging on dozens of USFS sales I often wondered about marking criteria.

    We did a helicopter sale near Randle, Wa. around 1999, it was supposed to be to enhance owl habitat in an area that burned around 1930, I can only assume it was to speed the stand toward “old growth” status. The problem for me was they didn’t take enough stems to actually speed up growth. I’m not a forester but have worked on a lot of private land and have cut commercialy thinned timber and have seen by growth rings what the increased growth results from a thin.

    I guess I’m asking why so many stems were left in this case, what were other possible criteria, it just seemed counterintuitive to me at the time. It was also fun to get back in that neck of the woods as I spent 6 months in Randle salvage logging a couple years after St. Helens in the early 80’s. It’s where I learned to cut timber.

    • Mike makes a good point. Can thinning a 2nd-growth Douglas-fir forest “speed” the stand toward old-growth status? Another way of asking the question, do wide growth rings an old-growth forest make?

      The classic “Ecological Characteristics of Old-Growth Douglas-fir Forests” summarizes: “Most of the distinctive features of old-growth forests can be related to four structural features: (1) large, live old-growth trees, (2) large snags, (3) large logs on land, and (4) large logs in streams.” Thinning does not contribute to items 2 through 4. In fact, insofar as thinning removes incipient mortality, it might work against the development of snags and down logs.

      The authors’ warning that “Recreation of old-growth conditions through long rotations is theoretically possible but clearly unproved at this time,” is as true today as in 1981. Then, it was inconceivable to the authors that anything more than “5 percent or less of the land base” would be protected old-growth. Thus the authors’ emphasis on making the best of a bad situation by managing for “individual features,” e.g., some big, live trees.

    • Mike: I had a tree planting crew and a precommercial thinning crew in the Mt. St. Helens area when it blew. My Mom was from Cougar, Washington where my uncles and grandfather had logged since the early 1900s — where most of the land had burned over along the Lewis River during the 1902 Yacolt Burn. I was supposed to start a USFS thinning job of a few hundred acres out of Morton that I had negotiated before the eruption, but it was one of a very few contracts I backed out of because of all the ash — people were afraid of what it would do to our chain saws, and I was afraid of what it would do to my employee’s lungs. I never really heard of any actual problems in those regards, but after watching a mountain I had known my whole life blow its top I didn’t want to take any chances.

  8. Mike and Andy:

    Thinning trees makes them grow faster, not older. I think a huge problem has even been the definitional idea of “old-growth habitat.” Why are stands of actual old-growth (traditionally 200 years, NOT 80- or 100- or 120-year old large second growth) expected to have large logs on the land or in streams? That was/is just an arbitrary definition made up by people who seem to oppose logging on federal lands. Same with snags. And why are these “ecological” characteristics, as opposed to just plain old “characteristics?” I think a lot of the work done in 1981 was far more political than biological and the Clinton Plan and “critical ESA habitat” seemed to grow out of those politics.

    There is a lot of evidence that 200-year old Douglas-fir, Sitka spruce, white oak, and ponderosa pine within the range of spotted owls often occurred in stands w/o a bunch of wood on the forest floor or in the creeks, or without a large number of snags. Too, it is hard to find evidence that they have ever really been much more than 10% of the environment if measured on a regional basis, such as the range of spotted owls. The historical evidence to back these claims (maps, photos, eyewitness accounts, timber cruises, and land surveys) has been generally available for the past 20 years, at least, and has been routinely ignored by the “critical habitat” political types. For some reason.

    Ignoring the effects of people on historical stand structures, and redefining the word “old” in “old-growth (or defining “seral stages” in terms of age classes) has been an effective way to help stop logging in our federal forests. The “science” that came up with this stuff needs to be challenged at some point with actual documentation, not computer models based on assumptions. These assertions were developed before digital photography, Internet communications, GPS, and satellite imagery. They have been discounted with ring counts and arithmetic. Why do we keep hanging on to these things? When do scientists begin critically reviewing the data that form the basis of these claims?

  9. For those who persist in believing that there is no positive scientific basis for Thinning our National Forests. This article demonstrates basic plant physiology as a part of forestry education even in prehistoric times when I was in college. Although this is disputed by many greenies, countless statistically sound research studies all over the US and on the ground validation at operational scales consistently supports this cornerstone scientific principle.


    1) “168 different plots of land between 1944 and 1988”
    2) “removing most of the brush and half of the trees made the remaining trees grow so much bigger and faster that in the end you ended up with just as much biomass as before you thinned — except now you had a much lower risk of catastrophic crown fires”
    3) “researchers found that in stands suffering from significant tree death from things like beetles and mistletoe, you could thin even more severely and end up with more wood than you started with”
    4) “aggressive thinning also significantly reduced the buildup of fuel on the ground. That would make wildfires much less destructive, since fires that consume large buildups of dead wood and brush on the ground can effectively sterilize the soil — and make it less able to absorb water” (my addition: and therefore less likely to cause significant erosion due to the increased volume and force of runoff)
    5) “removing shrubs from the understory when combined with thinning also boosts overall tree growth — apparently by reducing the competition for water. Thinning a stand and removing the brush also results in a net reduction in the release of carbon into the atmosphere, by reducing both wildfires and wood decay”

  10. I see wide agreement from many enviros, not all, but many, on the benefits of thinning such pine stands. It is higher elevation varied, mixed conifer species stands that pose more questions about appropriate approaches.

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