That's very interesting, thank you. Did they do any studies on deciduous trees too?

Yes, I reference that in a paragraph just past the middle of my summary. The callus growth is stimulated by a cut into the branch collar much as it is with conifers, making the healing, or "occlusion," of the cut more rapid. But of course with any kind of tree, conifer or hardwood, this more rapid callus growth cannot make up for a flush pruning cut that makes the area to be occluded massively larger than a cut that leaves the collar intact or cuts into the collar only partially.

--Spruce

Spruce, thanks so much for making the effort to share such a long article with the forum. I appreciated it - the moreso as I have to clean up a water oak - lots of dead, lower and interior branches - and limb up an unknown maple, so branches don't start hitting the porch roof. Now I have a good idea of how to go about it - or should I say, a better idea?

I am glad you appreciate my efforts to bring the information in this article to you all. Just a few more thoughts.

First, I see I garbled the reference at the beginning--it should read Volume 105, Number 3. The article is on pages 131 to 138.

Next, The Journal of Forestry is the "gold standard" for publications on forestry and forest research. For forestry it is analogous to "The New England Journal of Medicine" for medical research, or "Nature" for physics, or the PMLA for literature, etc. Also, The Society of American Foresters publishes several other journals, including Forest Science and regional journals on applied silviculture. The fact that this article was published in the "Flagship" journal has impressed me.

Next, it is ironic that Dr. Shigo whose work to some extent has focused on the tree's natural responses to injury and its ability to heal itself, etc., would have missed this crucial aspect of a tree's response system. This certainly points out the need for careful controlled comparative studies, and for studies that are completely objective and which are not unduly influenced by non-systematic observational data.

As to what this tells us in practical situations about how to prune our trees--it certainly can help. But on the other hand it makes decisions about exactly how to prune a specific tree in a specific situation much, much more complicated than they were before. Identifying clearly what the branch collar is in any specific situation is something that I think I have mastered, although it could be difficult for someone less experienced. But now with this new information, determining exactly how to make individual pruning cuts is far, far more complicated. Before we were faced with different kinds of trees having branch collars formed in a variety of ways and specific decisions had to be made to based on our recognition of the branch collar. Now we, if we are to do the best possible pruning job, need not only to recognize the branch collar, but also need to know more about each individual tree's response to a cut into the branch collar and how much that may stimulate the faster callus growth.

It is clear that in most situations we should not try to remove the entire branch collar to make a "flush" cut, except perhaps on some trees where this is possible without creating too large an area to be occluded. There is no evidence in this study to suggest that the stimulation of callus growth by cutting into the branch collar will stimulate it so much that it can occlude any size wound. So we need to exercise reasonable judgment. In essence, we are still faced with the conundrum. One specific kind of cut that this study suggests can be very effective, but which would violate the natural target pruning method of Dr. Shigo, is the making of a cut parallel with the trunk when the "target" method would have the cut angled outward to follow the borders of the branch collar. This kind of parallel cut would cut into the branch collar just a bit at the top of the cut, and more substantially at the base. This adjustment to the cutting method would make a larger area to be occluded, but not too much larger to be overcome by the more rapid callus growth. The advantages would be a cut that in many cases would look better on an ornamental tree if it did not make too large a wound, and which would in commercial forestry allow the tree to produce more clear-grained wood.

In some situations, cutting very deeply into the branch collar is not possible without doing serious harm to a tree. One case discussed in the article is with a ponderosa pine tree which a whorl of branches, each with a substantial branch collar. If a substantial portion of the branch collars were removed when making a pruning cut on this tree, the entire tree trunk would be girdled and the tree actually killed. This is, of course, and extreme case, but it clearly illustrates the kind of problems that can be created if this kind of pruning method were to be applied indiscriminately.

Well, thanks for your responses so far. If you have any more questions/thoughts, I will try to respond with more from the article.

--Spruce

Let me correct a serious oversight in my reporting on this very important article:

The author is Kevin L. O'Hara, University of California--Berkely, Department of Environmental Science, Policy and Management.

--Spruce

Spruce,

Thanks for posting this.

I just checked the Journal of Forestry online, and the article is available for purchase ($6) here:

http://www.ingentaconnect.com/content/saf/jof/2007/00000105/00000003/art00010;jsessionid=19n1up036vqms.victoria

Alex

Good work, spruceman. The JoF has not yet arrived on the left coast, but I'll be watching for it. I think Shigo's oversimplification was intentional -- to appeal to growers who want a clear simple rule of thumb. Unfortunately his penchant for new solutions often created a cult-like following of folks pleased to go along with a "rebel" with credentials.
This shows the benefit of peer review.

Very interesting, Spruceman. I just cut a fairly massive low limb (1 ft dia & 45' long) off my E. sycamore to provide more light for several trees/shrubs (on that 110 ft tree, the absense of the limb is hardly noticable). One practical aspect is that the limb was so large that cutting right at the branch collar was less strenuous than a much larger, "flusher" cut. We'll see how it goes, but I've seen good healing results in the past from cutting barely beyond the branch collar on forest trees.

In a way, the report makes sense in that cutting into the collar would stimulate faster healing since if the branch collar is completely undisturbed by the cut, it wouldn't seem to have as much impetus to start producing callous tissue.

A few more thoughts:

For those of us who have been pruning using Shigo's "natural target method" of preserving the branch collar, I would not worry. When pruning relatively small branches from trees for the usual purposes we do, this method of pruning is going to be OK. This does not have the really bad effects of leaving a branch stub outside the branch collar, or pruning with an axe, which can leave really ugly wounds. I am not going out and re-doing the pruning I did this winter. So, don't worry about what you have been doing.

This study does not address the kind of issues of fungal infection that can happen when really large branches are cut off trees for special reasons. As many of you know I have been advocating the use of liquid copper fungicide applications to prevent rot from entering the cut, which in most cases of pruning large branches, can require 15 to 20 years or more to be occluded.

Beng: I would wonder if when really large branches are cut off--and by "large" I mean something like 4 inches in a slow growing tree to branches somewhat larger on larger trees, sometimes I would guess over a foot or more in branch diameter--if the issue of making a close cut well into the branch collar might involve a trade-off that is substantially different from the kind of routine pruning that is considered in this article. To determine the differences between different types of pruning cuts for large branches would require more research. One obvious question would be how well sustained is the stimulation of callus growth when the area to be occluded is really large. I would suggest that when we talk about the removal of large branches we use the term "tree surgery" if what we are dealing with is shown to be substantially different.

As for Dr. Shigo--yes, what he advocates has the benefit of simplicity and clarity. The problem is that one of the main points he made--the harm done by cutting into the branch collar--is flat wrong.

I think the most disturbing aspect of Shigo's work, is what in this article politely described as "a disconnect between the extensive research in the past and the observational studies that led to natural target pruning." Dr. Shigos ignorance of, or deliberate disregard of, previous research is something I find completely reprehensible. As a Ph.D. student writing my dissertation, the one most basic thing I was required to do was to ferret out virtually any and all prior research that could have a bearing on the issues I was considering. Dr. Shigo liked to call himself "Dr.," something that the vast majority of us who have earned a Ph.D. degree decline to do. But in his own studies he apparently made no attempt to show any respect for the work that had been done by others before him, and showed no respect for us who assumed that as a scholar, using "Dr." as a part of his name, he would approach his research is a way that met the most basic standards of scholarship.

The damage that this kind of disregard for the basic principles of scholarship spreads. Having been helped on more than one occasion when I had questions regarding thinning my Norway spruce plantations by Professor Nyland at SUNY Syracuse, my thoughts went immediately to him and the awkwardness he must feel in having relied on a source that has now been proven to be bogus, for a portion, if only a very, very small portion, of his textbook on silviculture. I know first hand that it is impossible to go through all ones sources that one may rely on when doing research, to verify the quality of the scholarship on which they are based. This is especially difficult when writing a textbook which of necessity will usually cover a very wide range of material.

--Spruce

Any chances of getting a pdf copy of the J.For. paper? I'd like to read it.

Resin

Alex reports it is available on-line for $6, but I don't know what the format is. I would assume this is the only place you could get it. It is copyrighted and I think I pushed the limits of what would be permitted in the amount I quoted, although I can't imagine that SAF would come after me if I did in fact violate the letter of the copyright law.

--Spruce

So we're still using the word 'heal' in this forum to describe a tree's response to wounding? Already on the wrong track. And for many of us who followed Shigos work, it was one of many sources of info, not exclusive.

Finally, if we are to turn the entire industry around now, because of ONE new paper, I've got really bad news. The trees have been doing it wrong all these millenia. Anyone ever observe a forest tree with a spot where a branch was shed fairly recently-not completely grown over with new tissue-? Yep, they shed these branches at the branch collar......damn!

+oM

Resin,

I don't know the culture of the forestry researchers, but in other areas of biology, corresponding authors are usually happy to send a reprint or pdf to anyone who asks for it. It shouldn't be too hard to track down his e-mail address. I should have mentioned that in my original post.

Alex

alexander3 is right. Go to the dept. of ESPM at Berkeley's website and you can probably find an email address for Kevin. He will likely oblige with a pdf copy. Actual hardcopy reprints seem to be nearly extinct.

Wisconsitom:

I think you have misunderstood what this article is--it is not just "ONE new paper." In the first paragraph in my report on this paper I wrote "This article is a review of research and observations on the subject going as far back as the 18 and 19th centuries and continuing up to the present." Prior to writing this article the author published a bibliography on the subject which has 75 pages. Since that bibliography was published I would guess that his own bibliography on the subject is somewhat larger. Perhaps I should have not titled my original post so politely. This paper simply "blows out of the Water," if I can use another unscientific metaphor, the current thinking on the proper way to prune a tree. How about another one--"completely destroys and overturns." The author has published one specific study on the subject of his own. The paper is primarily based on a review of the work of the others who have preceeded him. It is Dr. Shigo who chose to ignore all this prior work, as if it added up to NOTHING. I am disgusted and I will not maintain any pretense of politeness about the matter. Sorry!

Also, you can slam me for using the word "healing," which I could argue is a natural word, although perhaps not a scientific one, for the "occlusion" of a pruning cut, but that kind of nit picking is not going to earn any points with me, and no points for the revered Dr. Shigo if this is how his followers want to deal with those who raise questions about the legitimacy or his research, which some of you may remember I had questioned more than once before on other points in these forums before this article appeared.

As for the author and his e-mail address: ohara@nature.berkeley.edu

--Spruce

I'm sure not jumping on this bandwagon yet! Discussion is valuable and informative. Where are the years and years of study and documentation? I've seen waaaaaay too much personal evidence in support of many of Alex Shigo's observations to toss them out, just yet. ;-)

Sounds to me like someone has been personally and professionally put off by Shigo and is now making up for lost time. This kind of professional jealousy is rampant in the industry.

Are we open for new information and theories? Absolutely! I'd personally be excited about it. I haven't seen anything yet that I'd swoon over. ;-)

Well, I am swooning, but at the same time feeling guilty. I have been pruning trees for many, many years--literally tens of thousands. I bought into this method of always pruning outside the branch collar and was a strong advocate of it, as those who remember my posts can attest.

But now I am having flashbacks, and embarassing ones at that, because I ignored what I had observed. On quite a number of occasions I had noticed something that until now I did not understand the importance of. Somehow these observations got filed away in my brain, but at the time I ignored them or found some explanation that was not good.

Here is what I have been observing for years. When I have pruned white pine and Norway spruce trees I have so many to prune I work very, very fast. At times I have cut into the branch collar by mistake. I prune my trees in stages, so after I do the initial pruning from ground level to something like 7 feet, I go back with a pole pruner and prune up higher, and then again still higher, until some of my trees are pruned up to as much as 42 feet.

So I see the aftermath of my pruning when I go bact to the same trees to prune higher see and the aftermath of the occasional time I cut into the branch collar, sometimes only slightly.

I had noticed this accelerated callus growth, but I had written it off to having cut close enough to the trunk to have cut away all the bark, making the start of callus growth easier to notice. But in retrospect--picturing in my mind now what I was seeing--this growth was far too rapid to be explained that way. I think I now have the explanation. The next chance I get I will go back and do a count of these instances when I missed my cut and got into the branch collar.

I am old enough now to have had a number of these experiences of seeing things and not understanding what I was seeing. It has made me very humble and skeptical of myself. Unfortunately, some other people become angry or testy at me when I seem to be skeptical of them or what they report they have observed.

Rhizo: If you are accusing ME of prefessional jealousy of Dr. Shigo, save your energy. First, knowing what I now know, there is litttle to be jealous of. Second, I spent my entire working career as a professor of English, not forestry or arboriculture. My anger at Dr. Shigo comes from my intense love of trees. I think the much of what he has advocated has been bad for the care of trees, especially his insistence on the extreme effectiveness of a tree's ability to compartmentalize and wall off fungal rots that can enter through wounds to a tree trunk. His insistence that a tree can defend itself from all fungal invaders is patently silly and is probably the most important reason why the use of agents such as liquid copper fingicide, which I have been advocating (along with research on its effectiveness) have not been tried or have been rejected because they are deemed unnecessary.

Perhaps Dr. Shigo has made some significant contributions, but at the very least a thorough and objective review of his work has to be undertaken to determine what is nonsense (we should not cut into the branch collar, etc.) and what is not.

Anyway, I can see that any change in pruning practices will be very slow in coming, in spite of this article. This is sad.

--Spruce

I've noticed too that there seems to be a passion with some to bash Shigo. I dunno...I first became aware of his work in 1980 when my grandmother, rest her soul, who was an excellent gardener, mentioned something she had read about the use of asphaltic wound dressings not being helpful. It took the department where I work ten years to completely abandon their use, so yes, change comes slowly in this industry. And that's probably a good thing. The "latest findings" do not always pan out, now do they?

I get annoyed when people who profess to be wise in the way of trees use sloppy terminology. That's why I hit you up on the "healing" thing. It is simply NOT what happens. Healing is the replacement of damaged cells by new ones. Woody plants-all plants really- cannot do this. They (woody plants) can wall off wounds, chemically and physically. Hence their ability to live long lives despite wind storms, critters gnawing, what-have-you.

I did realize that this study was a review and compendium of past studies. Nothing wrong with that. It's another way to advance knowledge.

BTW, I'm curious as to how you and some others are so certain as to what previous work Shigo did or did not review as he set about developing his theories. Were you closely associated in some way?

I must know a couple hundred certified arborists. Their certification shows them to be among that group of arborists who have made some effort towards staying abreast of new developments. Not one of these people has what I would call a sycophantic attitude towards Shigo. All could be said to have taken the direction of his work with a grain of salt at one time or another. Yet, we see over time the tendency for his theories to be born out by what happens in the field. Flush cuts leading to "frost cracks". Decay pockets where flush cuts have been made or where branches were allowed to tear when removed.

I think you're a good guy, Spruce. And after all, we share in common the love for the same species to a near fanatical degree. But this just strikes me as reactionary. And I still think the trees know what they're doing when they shed a no longer productive branch........at exactly the branch collar.

+oM

No one has mentioned it, but in bonsai, branches are routinely cut flush with the trunk, and the bark then allowed to heal (or callous or whatever you want to call it) over, and within a few months to a year or so you can't tell anything was ever there. There are a few trees that don't heal or cover over very well, e.g. Ginkgo, so branch pruning has to be pretty selective as far as esthetics go, but generally (especially with conifers), it's the method used by all bonsai-ists, and only occasionally is any kind of sealant or paste applied afterward. There are special cutters used that create a very slight depression in the trunk so that when the bark covers it over, it's flush and smooth.

Wisconsiton:

What is clear from Professor OHaras research is that there was ample evidence in the literature prior to Dr. Shigos publications that contradicted his findings and Dr. Shigo was either unaware of this or deliberately did not cite it and/or deliberately chose not to show, if he believed it to be the case, that this research done by a good number of others was faulty. As I said before, this violates a basic requirement of good research and scholarship. In addition, Professor OHara points out that Dr. Shigos work is primarily based on "observational descriptions of tree responses to injury; there is a general lack of quantities data and no statistical comparisons of pruning methods."

Now, if my pointing this out, and saying that I question Dr. Shigos work based on both his ignorance of or deliberate disregard of all the research that has been done before him, and the lack of balance and thoroughness in his research methods, strikes you as "reactionary," I am not sure where we go from here. You end by saying that you think "I am "a good guy" in spite of my insistence on good scholarship and research methods. I do think I am a good guy, but the idea that this may be in spite of my strong beliefs in the principles of good scholarship and sound research methods leaves me speechless! I wonder what they are teaching in the universities these days.

As for the word "heal." I wont quote dictionary definitions for you except just this one from Websters: "to become closed or scarred: said of a wound." Now if I am engaged in a scientific discussion with others engaged in the same science and familiar with all the specific terminology that has become standard use, then I will use that terminology. But when I am communication in other kinds of situations, with friends and neighbors and/or the people in this forum, I do not feel the same constraint to use scientific terminology. I would question how many people when I talk about a wound to a tree trunk "healing over" would not understand what I mean or would think that I was somehow ignorant of the differences between the healing of a tree and the healing of a wound to human or animal flesh.

In fact the word "healing" is often used to describe a much broader variety of things, such as one saying that a relationship between two people can be "healed." If we reject usages like this we reject too much that is essential to our ability to use language to communicate. The use of metaphor to extend the meanings of words is basic to the nature language itself. But my usage of the term "heal" in this discussion does not really rise to the level of what we usually think of as metaphor. I think my use is very, very close to the root meaning of this word.

But, if this discussion continues I will do my best when addressing you to use the word "occlude when describing the process by which a tree grows callus tissue to cover a pruning cut.

--Spruce

spelling error, paragraph one, last sentence, "quantitative" data. Sorry, I thought I was hitting preview but hit submit instead.

--Spruce

rhizo's suggestion that O'Hara went to the trouble of writing his review in order to get off some shots at Shigo is absurd and undeserving of mention. I knew the late Alex Shigo, and I know Kevin O'Hara. In 1988 I invited Shigo to give a keynote talk at a forestry conference on the campus where I was employed. I chose him because he had the reputation of being imaginative and an effective speaker. He did a good job, and stirred up some fruitful discussion on compartmentalization of decay. I was aware that some forest pathologists felt he tended to jump to conclusions, but that was okay with me, since ideas eventually rise or fall on their merits.
I knew Kevin O'Hara in my role as editor of the Western Journal of Applied Forestry, to which he submitted at least one manuscript that I recall (it was on pruning, and I accepted it for publication) and I have heard him give papers at silviculture meetings. I regard him as one of the more thoughtful silviculturists I have run into, and as an honest and ethical researcher without an axe to grind. His current paper was refereed before acceptance, it makes no personal digs, and it understates what he might justifiably have said about Shigo's lack of good methodology. I see no evidence of ulterior motives in it, and as an editor I feel well qualified to detect such undertones.
I just read O'Hara's paper, and spruceman's description of it is accurate and unbiased.

Plants don't heal? How about the islets of callus tissue underlain with cambial cells that replace dead cambium on surfaces stripped of their bark? Not common, but it occurs.

Well Spruce, at the age of 51, I'm not sure what "they" are teaching at university these days! But I do know that when I'm teaching (adjunct faculty at local technical college), I will still be recommending that pruning cuts be made just outside the branch collar. There's a long way to go before this gets turned around. In fact, almost assuredly, the debate will linger after we're all dead and gone.

I'm done with this one. I leave with the hope that the trees eventually get it right.

+oM

Tom:

I think you are right. Here is what I think will happen. After a few years all the silvicultural textbooks will have new revised editions published and these will reflect Professor O'Hara's research. But Dr. Shigo's books will continue to be published for a long, long time to come and these books will probably have more influence than the revised textbooks, at least among the general public and the arborist community.

As for your own practice of always cutting outside the branch collar--as I said earlier, I don't think this will be a really bad thing. The evidence presented by Professor O'Hara is that it may not reflect the best available practice, but if arborists continue to avoid cutting into the branch collar, this will not result in the destruction of large numbers of ornamental trees. Most pruning cuts, especially of smaller branches do not become infected, except on a few species, whether the cut is inside the branch collar(done properly, not indescriminate flush cuts)or outside.

The most important impact of Professor O'Hara's work will be on silviculture in forest plantations or intensively managed natural stands. What he shows is that it is possible to prune branches significantly closer to the stem than has been recently assumed without delaying the covering of the cut with callus, but in fact hastening it, and without an increasing the risk of infection of the pruning cut or serious wood discoloration. The potential for increasing the production of high quality wood is very large.

--Spruce

Hi everyone,
As the author of this paper, it is really great to see a discussion on this important aspect of pruning. I would be happy to send an eletronic (pdf) copy of this paper to anyone who wants one. The paper focuses primarily on forest pruning where the objective is enhancement of wood quality for timber production. But it has many implications for other types of tree pruning as well. If you want a copy, just send me an email at:
ohara@nature.berkeley.edu

Thank you!

Kevin O'Hara

Spruce:

After summarizing the content of the article, you state, "... there is more than one way to skin a cat (i.e. effective pruning can be done in a variety of ways) and not all cats are alike (i.e. not all trees show the same response to a given pruning method).

I think this is almost universally true with living things - trees or people. One size rarely does fit all (although "one size fits all" solutions are appealing and popular).

You say that many / most pruning guidelines are based on Dr. Shigo's work. Are you aware of any guidelines (for those of us who are not professionals in the field) based on Dr. O'Hara's research?

Many thanks,
Pam

Pam:

Professor OHaras primary research interest is pruning in forest stands, and based on his own research and a large body of research by others, he can make some general recommendations, but perhaps not a general set of guidelines that can be applied in all situations. Anyway, to answer your specific question, I think that all the currently published pruning guidelines are based on the ideas of Dr. Shigo.

But if it can be of any help, I will try to boil down his article to some practical applications. I may be repeating what I have said in previous posts, so forgive me. But to summarize what I think I could take as guidelines from this article, it seems to me that the most important point is that cutting into the branch collar, at least a little way, can have a very beneficial effect in stimulating callus growth. Next, in terms of how to make a specific pruning cut, a cut parallel to the stem that is as close as possible to the stem without making the cut massively larger as a flush cut might do, can be very effective in many, if not most kinds of trees in a commercial forest. Generally in forest stands branches should be pruned as early as possible and stands should be kept reasonably dense so limbs do not become too large when the trees are still young. These may be the main points.

As for pruning ornamental trees, which is what most of us are primarily concerned with, I think similar principles can apply. If we want a tree to have a certain shape, and want the tree to be pruned up to a certain height, the sooner we can prune without removing too much foliage, affecting the overall growth of a tree, the better. A cut at least part way into the branch collar is also a good idea in that it will stimulate faster callus growth. The motivation for the parallel cut well into the branch collar is primarily for timber production in forest stands. I think the importance of this finding for pruning ornamental trees may depend on your own sense of what looks good. If a tree is grown for ornamental purposes, keeping the "defect core" of the tree small should be of no concern. If I can speak for professor OHara based on my understanding of the article, and I think I can here with at least some confidence, I think that the concern of Dr. Shigo for following the borders of the branch collar even when the branch collar is at a strong angle to the trunk is misplaced. If following the branch collar results in a cut that is angled outward leaving the lower corner of the collar protruding out some distance, I believe he would recommend a cut into the branch collar that is to at least some degree more parallel to the trunk so that this lower protruding corner is removed. The tree will look better and the cut will occlude faster. I think this will be one of the main things I will take away from this article for my own ornamental tree pruning.

But if a branch is large, and cutting into the branch collar can make a very large area to be occluded, some reasonable judgment should be used. This is something that OHara would not normally be concerned with in forest pruning. Here I think it would be difficult for him to make any specific recommendations without knowing the particulars of a given case--the species of tree (different kinds of trees may have callus growth at different rates), the individual tree (of course individual trees will vary based on their vigor and growth rate), and different kinds of trees are more or less likely to get fungal infections. My own take away here is that when pruning a very large branch cutting at least a bit, if not substantially into the branch collar will stimulate callus growth and will not make the area of the cut so much larger that it will take longer to occlude. I think what the article suggests is that even when pruning large branches a cut into the branch collar will stimulate callus growth so that the cut will actually occlude faster--just how much faster and how well sustained the faster callus growth may be the article does not directly address. But as I am sure you know, I will treat any large pruning cuts I make with liquid copper fungicide to reduce or eliminate the risk of fungal infections.

Well, I hope this helps. As I said in a previous post, I think silviculture text books will be revised with their next editions to reflect Professor OHaras findings. Some of these text book writers will be better able than I to translate his findings into some systematic recommendations. But what we will ultimately have will be something more complicated, or at least more variable, than what we have now in that there will be more of an attempt to deal with specific pruning situations and specific species of trees. I think one very important result of OHaras article will be a boost to further research. This article makes it clear that we do not have an answer that is as good as we thought we had. With his summary of so much prior research, Professor OHara firmly establishes the general benefits of cutting into the branch collar--the weight of evidence for this is very large. As a result, the whole area will be much more open for inquiry (new research) than before. I have never been involved in doing any forestry research, but I have been reading forest research studies for many, many years. I cant think of any article I have ever read that is more important or has broader beneficial effects on the care of trees, than this one.

--Spruce

Spuce:

Thanks for taking the time to put Professor O'Hara's findings and conclusions into a more understandable form for the lay person. Your summary is useful for those of us who are following this discussion, but who lack the expertise to put this research into practice.

I have many books that include sections on pruning. Out of curiosity, I checked several - the advice was nearly identical.

I expect Dr. O'Hara's findings will stimulate research because this opens up a very large, important area to further study and investigation. Current practices are being questioned, perhaps tossed out. I also anticipate resistance to his findings from some quarters. At least, this is how these issues unfold in other areas of scientific and medical research. In the end, this will stimulate debate, lead to more research, and educate people about the new findings.

Thanks for telling us about the article and its ramifications. Your excitement is contagious. I think I'll take Dr. O'Hara up on his offer to email the article to interested individuals.

Take care,
Pam

Pam:

Yes. I have heard of resistance to research on pruning methods prior to this article. I don't know the extent of that resistance--perhaps a large part of it has been a reluctance of researchers to become involved in an area of research that may have seemed to have been settled in regard to at least some of the main points. But I know it has gone beyond this.

In any case, this article changes everything. In the community of foresters and forest research supported by universities in this and I should think other countries, I would be surprized to see much if any further resistance to wide ranging research on pruning and other related areas. The placement of this article in the Journal of Forestry is key--congratulations to Dr. O'Hara! It cannot be overlooked or forgotten.

--Spruce

Interesting research paper Spruceman. Obviously contrary to what I've been doing for 40 years!!

Does the author give theories why flush pruning would heal faster?

Also, does this mean, when we prune smaller twigs that we should flush cut adjacent to a bud rather than leave a little stub?

The problem I'm having with the new paper is why would that half-inch or one-inch stub not heal very similarly to the flush cut method?

Is it true that Shigo insisted that "a tree can defend itself from all fungal invaders?" I mean, the CODIT response is a real thing, but I wasn't aware that he made such an extraordinary claim as that.

Sounds like interesting work, and it sounds credible on its face, based on what I've seen on the field. I've let my SAF membership lapse, but I'll take Dr. O'Hara up on his offer of a .pdf copy.

rdak:

You are not alone--I have been pruning for as long or longer than you and the suggestions in this paper are something it will take me just a little time to get used to. I suggest that you contact Professor O'Hara and take him up on his offer to send the paper to all interested parties.

But I will try to answer your questions here: First, he is not recommending "flush" pruning. For forest trees he is recommending a "close cut" will into the branch collar and more or less parallel to the trunk, if possible.

Second, a cut into the branch collar does something to stimulate callus growth. The article doesn't go into specifics about why this might occur. I have a couple of theories I would like to test, but since I am untrained in this kind of research, I would rather not try to speculate here. But in general my guess would be that there may be something different about the cambium cells in the branch collar from what is in the branch. Also, the cut into the branch beyond the collar is strictly cross-grain, here the cut may be more at an angle to the fibers. I don't have the article now before me, but I think this issue was mentioned. And then finally, the branch collar grows faster than the branch itself, so that could be a simple explanation, but for me probably not a sufficient one.

As for pruning small twigs, I think this is a different issue. Cutting right next to a bud may be too close if the growth of that bud is what one is aiming for. I think this kind of pruning is substantially different from the pruning discussed in the article because the occlusion of any cut that is made is not an issue.

As for your last question, I am not sure what you mean by leaving a half inch or one inch stub. Prior to this article, The accepted guidelines for pruning don't recommend leaving a branch stub, just the collar. What Professor O'Hara has found in the previous research, as well as his own research, is that a cut into the branch collar will in most cases of pruning, except, perhaps, for very large limbs, stimulate callus growth so the cut is occluded faster than a cut that is right up to the branch collar, but which leaves it entirely intact.

--Spruce

Yes, you have caught me in an exaggeration--I was reacting to the cartoon in the little pamphlet published by Dr. Shigo. It shows a tree with its branch reaching down to swipe away the attempts of a person to apply something to a scrape on the tree trunk to keep fungus from infecting it. The implication of this cartoon is that the tree can take care of itself. Well, trees do have some defenses against fungal invaders, but in my observations, these defenses in many, many cases are not adequate. Trees often get scrapes or knocks to their trunks that removes or kills the bark, and they often become infected with one or more fungi, and this infection proceeds to weaken the tree, and in many cases, eventually kills it. The CODIT response is relatively weak, in my own informal observations, when the injury is to the lower part of a tree trunk and is at least several in diameter. And scrapes that have some vertical length are more susceptible than those that are very short but not excessively wide. Well, I am getting into to much detail here.

There have been studies of the scrapes and knocks to tree trunks that occur during logging operations that show that a very, very high percentage of these become infected in as little as 10 years, leading to a serious loss and degrade of the wood these trees produce. I have not mentioned it here in these forums before, but I have on a couple of occasions had logging done that resulted in a number of such scrapes (I do most of my logging myself and am careful to avoid these scrapes). I treated about 60 or 70 such scrapes with the liquid copper fungicide I have been advocating here and to my knowledge, not one of these sites has any fungal infection, in some cases after much more than 10 years.

So, that little tree in Shigos cartoon, if it knew what was good for it, would not swipe my hand away!

--Spruce

Thanks for the info. Spruceman. Interesting! After all these years of staying away from the branch collar it might have been beneficial to cut into the branch collar all along. Learn something new everyday!

However, I'm going to have to get steadier hands before trying out this new method!

No offense intended regarding the Shigo exaggeration, spruceman - I just feel that it's really important to accurately represent everyone's views, particularly when you're challenging the orthodoxy. It would be nice to see a study of the copper fungicide (copper sulfate?) wound treatment you're advocating. My main concern would be the potential for phytotoxicity.

The article is very interesting and definitely has me thinking. The author wisely notes that one universal pruning method may not be ideal for all species and all situations, but I think he makes an excellent case against the status of the natural target pruning method as the final word in tree pruning.

saccharum:

No offense--I am a natural exaggerater, but do my best to restrain myself.

As for the copper fungicide's toxicity. I have noted in these forums before my suspicion that it has some toxicity to sapwood if it soaks down inside a tree and gets at it from the inside. I have not reported all the things I have tried with this, but I did try applying this stuff to real extremes, and at what I would call almost ridiculous over applications I suspect some marginal toxicity. One pine tree that I poured this stuff on in amounts I cannot accurately document had a portion of the side of the trunk under the application zone die. But this was a tree that a storm broke half of off, the broken part being about 14 inches in diameter, and where it broke there was a sunken area where I could actually pool this stuff. But in my experience, the part of the trunk under this really huge broken area may have died anyway.

In another instance where I applied it very, very liberally I noticed some bleeding beneath the cut, which was a cut to remove half of a forked tree and the cut was about 5 inches across. I did this experimental overapplication on this tree, a Norway spruce, because it was a weak tree growing in the shade of other spruces and a white pine. A stronger tree growing in full sun may not have shown the same symptom. The tree, however, is still alive and has not shown any loss of vigor. It is in substantial shade but is "plugging along" nicely considering that. Both of these instances were cases where the cut or the break was across the grain and the cut or break faced upwards and absorbed all the rain that fell also.

I noticed no other instance of anything I would suspect was a toxic effect, and for a while--until I learned better, I applied more than needed. So I think it is in all probability safe.

As for research--I have been talking to people for at least 20 years in several universities trying to get someone interested, but no luck so far. This liquid copper fungicide is the third thing I tried--it seemed obvious very soon that it was working, so I have tried nothing else since. But of course there are other things one could try. Part of my reason for trying this liquid copper fungicide is that it was my understanding that the copper itself was the active agent, and I thought that the copper would have some stability in the outdoor environment and would not break down so fast as other fungicidal compounds. Also, it is my understanding that the "liquid" copper fungicide is, in fact, a true liquid solution, and as such it would soak into the wood in a way that a wettable powder would not.

A great many trees get fungal infections through injuries to the trunk or from pruning cuts made to remove very large limbs. It pains me to see this and I am convinced (I understand research needs to be done, if only to convince others) that it can be easily prevented. Many of the trees are trees loved by their owners, and in many cases these trees have a monetary value that would exceed several thousands of dollars. What a waste!

Oh, I must note--even though I admit to a frequent tendency to exaggerate, I am not exaggerating about the ability of this liquid copper fungicide to stop fungal infections. Just to be clear--over the last 20 years, I have probably used this stuff on 200 trees. About 60 or 70 of these were spruce and pine trees (Norway spruce, white pine, red pine) that were forked. I cut half the fork off, leaving big ugly cuts, mostly sloping, but not always. Some of these cuts were at least 6" across. Many took 10 to 15 years to occlude, and some, after 20 years have not yet occluded. I have seen no evidence that I could recognize of any fungal infection whatsoever. And the wood at the surface of these cuts is as fresh and hard as a board in a lumber yard. I am not exaggerating this one tiny, tiny bit.

I have also used this stuff on logging bumps and scrapes, some really huge, on various species of hardwood trees and hemlock, and as I reported above--no trace of fungal infection that I could detect.

I have tried to renew this stuff every year--in some cases I missed a year or two, especially on the logging wounds which require a lot of walking to get to every year. One thing I would like research to show is how often it is necessary to reapply this stuff. I have wanted to be on the safe side, hence my reapplication every year, as far as I have had time and energy. Getting to all the treated trees over the 300 acres I have is a four day job, and an exhausting one at that.

--Spruce

"Be open to learning new lessons even if they contradict the lessons you learned yesterday". (Ellen degeneres)