8 Jul 2008, 2:08pm
Federal forest policy Saving Forests
by admin

Old-Growth Trees vs Old-Growth Stands

For many veteran readers of SOS Forests, this post is going to seem repetitious. But we have many new readers and so please bear with me.

Old-growth are old trees. Generally speaking, true old-growth trees are those that germinated prior to Euro-American contact with the aboriginal (Native American) populations in a region. In Oregon true old-growth trees are 175+ years old.

In most regions, including all of Oregon, true old-growth trees arose in an age of frequent, regular, seasonal anthropogenic fire. Indian burning maintained prairies and savannas. Hence true old-growth trees were open-grown in open, park-like stands.

Following elimination and/or removal of Indian populations, the anthropogenic fires stopped. Thickets of young trees, so-called second growth, arose under the open canopies of the park-like stands. What resulted are multi-cohort forests.

Multi-cohort forests have 5 to 10 true old-growth trees per acre and the rest are second growth, sometimes numbering as many as 500+ trees per acre. The increased tree density makes those forests susceptible to catastrophic stand-replacing fires.

Previously, when the Indians were burning, fires would stay low to the ground and not kill many trees. In contrast, our modern fires kill all the trees, old and young alike.

It has been recognized that to save and preserve old-growth we must thin out the second growth, younger cohort trees. That was the gist of the important testimony given by Drs. Norm Johnson and Jerry Franklin last December [here].

No longer do forest scientists view entire stands as old-growth. That was the old paradigm. Today the general understanding is that only a few trees in most “old-growth” stands are actually old. The concept (forest condition) is called multi-cohortedness.

The new Sen. Ron Wyden discussion draft (the Oregon Forest Restoration and Old Growth Protection Act, no number that I am aware of yet) adopts this new paradigm understanding and calls for thinning in what were formerly thought of as old-growth stands. The draft includes provisions for protecting the old-growth trees in those stands, defined at this point as 120 to 150 years old. We can quibble about what age is required for a tree to officially become “old,” but the concept that most trees in “old” stands are not old is an important shift in regulatory thinking.

The purpose of thinning the younger trees is to protect and preserve the older ones, especially from catastrophic fire. In the interests of sustainability, some of the younger trees should also be left to fill in for older trees that will die eventually. But it is also important to open the stands so that the leave trees (those that remain after thinning) are widely spaced and do not have low-hanging limbs that would ladder fire into the crowns.

Fires are going to occur, whether ignited by lightning or by humans, deliberately or by accident. Our forests need to be prepared to receive fire without total mortality of all trees.

That type of thinning strives to re-create the open, park-like stands of yesteryear. More properly, such thinnings are called restoration forestry because their goal is to restore forests to pre-Contact structures and conditions.

Some believe that identifying old trees is a difficult process involving the increment coring of every tree. That is not the case. Old-growth (older cohort) trees exhibit many external characteristics that indicate their age. Rather simple and quick to use discriminant models can accurately categorize trees as old or young based on those external characteristics. Since there are few old trees in a given stand, usually some young ones should be left as well, further ensuring that no old ones need be cut.

Young trees are not perforce small trees. A Douglas-fir of 100 years old is second growth but can easily be 4-foot in diameter in many Oregon environments [here]. Diameter limits to thinning are stupid and worthless. Age and tree density (trees per acre) limits are much better controls that serve to restore fire-resiliency in forests while protecting true old-growth.

In addition and generally speaking, natural/cultural historical analyses of the prior forest and landscape conditions are required at the beginning of restoration projects to establish target tree densities. Much that is historically valuable could be lost in the rush to remodel landscapes based on whims of the moment rather than scientific/historical accuracy.

There are a few pieces of legislation under consideration right now. Wyden’s draft is one, S. 2593 (the Forest Landscape Restoration Act of 2008) is another. It is vital that any new legislation discern the difference between old-growth trees and old-growth stands. The former are true features of forests, the latter are not. It is also vital that natural/cultural historical analyses be included in any forest legislation. We need both those elements to do true restoration forestry and thereby save our forests from catastrophic destruction.

8 Jul 2008, 3:01pm
by Bob Z.


That is a nice essay on old-growth. During most of the past century, most foresters, timberland owners, sawyers, and historians considered “old-growth” trees to be at least 200 years old, with some arguments opting for an age of at least 300 or even 400 years.

I like your definition better, for both reasoning and aging purposes. Two hundred years ago in Oregon, Lewis and Clark had just visited the Columbia River and documented the widespread decimation of local Indian communities by smallpox which they estimated had been introduced about 20 years earlier.

Two hundred twenty years ago, in 1788, Robert Gray sailed along the Oregon Coast, witnessing first-hand the existence of iron knives and smallpox (both indications of direct contact with Europeans, Africans, and European Americans) among local Indian people near the mouth of the Siletz River.

Many Oregon Coast and Columbia River trees dating to the 1788-1806 time period were sold and milled as second-growth during the past 150 years. Many of these trees likely germinated as a result of the collapsing human populations, and related contraction of land use in the region. Those trees that survive to this time are 200-220 years old. Whether they are labeled old-growth or second-growth is unimportant; their true value lies largely in their existence as irreplaceable historical markers delineating the massive changes in Oregon human cultures and forested landscapes that began to take shape during that time period.

As a result of this “natural history,” I would argue for definitions of several age classes of old-growth, beginning with yours near the youngest end of the scale. Pre-Columbian trees (515+ years old), as another example, certainly demand some sort of special consideration and attention.

In any and all cases, old-growth trees currently threatened by encroachment and wildfire (almost all of them), deserve and require immediate management attention before they become completely eliminated from the environment via insects, disease, over-crowding, and wildfire. The anti-logging factions have only hastened and exacerbated the process of old-growth elimination started by invasive European grazing and logging practices.

8 Jul 2008, 6:49pm
by bear bait

Bob and Mike: Are there species of trees that also indicate “old-growth” in multi-cohort stands? I think about yew, western red cedar, and sitka spruce, and to some extent, concolor and grand fir, like there is in the Tillamook second growth from fires prior to the 1933 Tillamook Burn. The true fir in that second growth stand is not unlike a sugar pine in the p. pine doug-fir shasta fir forests, as it is the tallest, straightest, biggest boled tree in the stand. I looked at a bunch of Weyerhaeuser ground years ago south of the North Umpqua and above Glide. The sugar pine was spectacular, albeit just a tree here and there, and survivors of multiple past fire events.

So what I would be getting to, is that it takes a long time for the mixed species to find themselves in the regrowth from prior stand removal fire. There are early pioneer species, and others that come in later. So, in that sense, I have to wonder about species composition as another factor in determining leave trees in a selective thinning process in established stands.

It is very easy, once you train your eye, to see the aboriginal managed forest in the uncut forests of today. You just see the big, the different, the tall, the dished bark, the color of the bark, and you know the trees that are old growth, and the ones that have grown since European contact decimated the native managers. And they are there, and will not be forever if only because some of the newer, more thrifty trees will muscle the old guys to the side in the fight for sunlight, water and nutrients. The big old trees die because they do not have the space to live, no matter how that space is to come about. And fire will kill them and the ones threatening them in the unmanaged forests of today.

I have often thought that after several hundred years, a group of trees has just about used up all the nutrients the soil in that spot of the world had to offer, and only by elimination of some trees were others able to survive. Fire is about nutrient availability and change. So is windfall, but so much slower. About the saddest sight where I live is seeing the old savannah oaks, maybe 500 years old, being over grown by the second growth doug fir weed. And man is at fault for that happening. A great many of the oldest trees in the Willamette Valley, and to the north have been lost to the best of intentions in forestry, and that is the establishment of softwood forests. The oaks were a granary of sorts, and for hundreds of centuries supported man and a host of other animals. To see the oaks cast aside so casually, with arrogance, sort of wounds my soul. Especially to have them replaced by something as common as a starling or a dandelion, that softwood squatter Douglas-fir.

I hope that Forestry can get its collective head out of its academic black hole, and once again be a force for good in the forest. Preservation is not forestry. It is storing milk in a jug in the refrigerator, with the hope that it will stay the same forever. Wrong. That is not how biological systems work, or how they came about. The wild was tended for thousands of years, and the concept of wilderness was nothing more than an elite European parlor game of the 18th and 19th centuries that had the wealthy off on explorations “of the wilderness” which was in reality a place where others worked, fought, and played. The parlor game has continued to be popular and has spawned the conservation movement which has now floundered on the shoals of incomplete science and urban parlor games gone bad.

Thanks, Bob and Mike, for explaining how things might be if people would understand what they really want is obtainable, but not without work and effort.

8 Jul 2008, 7:17pm
by Mike

In answer to your question, yes, there often is a different species mix between cohorts. However, it varies from site to site. Sugar pine is often predominant in the older cohort in many forests. It was a favored food source, as was ponderosa pine. Western red cedar also has been a species with a very ancient connection to people, so it appears in the older cohorts on some sites. Juniper was used for bows, and many ancient junipers still exist.

If a species was useful to people, they nurtured it. If not, they burned it.

Douglas-fir, once established, is hard to kill, so it is also found in older cohorts. Not that useful to the First Residents, but too tough to get rid of easily.

The true firs were (are) easy to kill. They are so pitchy they burn like torches when green. Very few true firs are true old-growth. Incense cedar is also easy to ignite. Despite it’s capacity for prolific seeding and abundance of regeneration, my studies have found few in the older cohorts of SW Oregon and the southern Oregon Cascades.

The varying species compositions of older cohorts have almost nothing to do with natural autecology (comparative ecology) or plant associations. The younger cohorts reflect competitive species strength, but not the older ones.

That’s why you can find stands where the older cohort is nearly pure pine and the younger cohorts nearly devoid of pine, with Douglas-fir, grand fir, and western larch in abundance. After a stand replacing fire in those habitats, ponderosa pine does not invade first either. There is no “natural” reason for the ponderosa pine to even be there, yet it dominates the older cohorts!

Those situations are reflective of and resulted from centuries of human manipulation. There is no other explanation. That is why doing the natural/cultural history studies is so important. The assumption that only Nature has been in charge is usually wrong and leads to incorrect analysis and prescriptions.

9 Jul 2008, 7:55am
by Tim B.

Bob, just another factoid to support the notion that European diseases had a profound effect on First People’s ability to continue traditional burning practices at the magnitude they had done prior to that unfortunate occurrence: the western edge of the Warner Creek Fire (burned east of Oakridge in 1991) was in a closed stand of 140 year old DF w/ a scattering of much older DF.

Many of those older trees got cut during mop-up activities since most had some amount of defect and fire got in them. I saved a wedge out of one of those trees and later counted the rings and fire scars. The tree was well over 400 years old. It had no visible fire scars on the outside of the bole but in the stem I counted a total of 9, all but the first fairly obviously fire scars. Those scars averaged one every 15 years (with three very small ones in 4 years in the inside of the healing callus tissue, indicating very light fires and, given the frequency, a conscious, intentional ignition.

That fire regime ended about 1750 according to the tree’s accounting, about the time that fir traders/mountain men are supposed to have come into this country. From that point on the interval between fire scars was about 150 years. The take homes for me were 1) the earlier frequent fire regime was burning in an open grassy forest; how else could you get a fire to burn sometimes every year, and 2) these were purposeful ignitions, since the 150 year interval indicates that is closer to the “natural” (i.e.climate driven) stand replacement fire regime.

9 Jul 2008, 9:00am
by bear bait

Thanks for the explanation. The only way to find answers is to ask, so if I bug you sometime with questions, it is just me trying to learn.

9 Jul 2008, 9:09am
by Mike

bear bait,

It was a very good question. Thank you. A key point. If the system was natural/deterministic, one would expect very similar species composition between cohorts. Instead the differences are stark, indicating something else was going on besides “plant associations.”

9 Jul 2008, 10:10pm
by Bob Z.

Thanks Tim (and bear bait):

This type of information and discussion is both interesting and important. I remain hopeful that some of our “wildlife habitat” advocates are paying attention!

Next point on the block: “riparian zones” (people like them).



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