Culling multi-stemmed trees

      Should multi-stemmed trees be thinned from your woodlot indiscriminately? July 9, 2003

I'm in Northeast PA and have a few acres of woodlot containing mostly cherry, maple, and ash.

Thinning is a bit overdue, but I've started tackling it this year. We use the thinned trees for firewood. Trees are nearly all 6" to 13" diameter, but the maples, particularly, are often multi-stemmed.

Should the multi-stemmed trees be culled without further consideration? My tendency is to do this, but in some areas this will leave substantial empty spaces.

Forum Responses
(Forestry Forum)
From contributor J:
How far from the ground level do the multi-stems occur? Some trees multi at ground level while some stem-out far enough from the ground to get a nice log.

Personally I would get the multi-stemmed trees out of the woods first. Just remember that a healthy forest/woods can sustain about .5-1.5 cords of wood product removed per acre per year, depending on species and growth rate.

You should not kill the multi-stemmed trees indiscriminately. If there is a good stem out of the bunch and it is a desirable species, leave the good stem and cut the other off at a 45 degree angle. If the stems are bigger than you are comfortable in cutting, then girdle them at least 3 times. Do not use herbicide on them, as you will kill the whole tree.

Many of our second growth forests regenerate through stump sprouts.

Lloyd Casey, forum technical advisor

From the original questioner:
I've been afraid of cutting some stems and leaving others; I'm nervous that this can (will?) give disease a foothold in the entire tree since the pruned ends can be large (6" diameter or even larger). But maybe that's not really anything to worry about...

From contributor J:
Is there a sealer on the market to keep disease and other undesirables from entering the wound?

Your concern about infection spreading from a removed stem to one that is left is warranted.

When you thin, you don't want to leave big gaps in the forest canopy or you lose potential for maximum photosynthesis.

Choose single stems over multiple stems for crop trees. If you need to leave multiple stems, you might want to consider leaving them intact if they can be harvested the next thinning.

If you really need to take part and leave one, obviously you would consider size and health in choosing which stem to leave, but also consider the closeness of the bases of the stems. If there is a wider crotch, infection is less likely. A U-shaped crotch rather than a V shape.

By cutting the trees at a 45 degree angle you prevent water from sitting on the stump, which goes a long way in delaying rot. Usually the main stem that is left prevents further stump sprouting until it is harvested. By cutting the poorer stems out, you push more growth on to the main stem and increase its growth. You should contact your local PA Bureau of Forestry Service Forester, who will provide a booklet on thinning stump sprouts and crop tree management.

A sealer is not necessary, as the tree will compartmentalize the stump that is left and contain the wound to the stump.

Lloyd Casey, forum technical advisor

If you do not cut the extra stems, what will you have in 10 years? If you cut and you end up with a good stem, great. If you cut and get a diseased tree, will that be worse than not cutting at all? Any research out there that answers this?

From contributor C:
Decay resistant species are more tolerant of thinning a multi-stem than non decay resistant species.

A "U" shape crotch is a better candidate than a "V" crotch, as the decay can occur in the crotch, not at the cut, although it is because of the cut that the rot occurs.

Try thinning your multi stems in fall and to an angle sufficient to keep water away. Winter will take care of drying the wound and prevent infection. I've just harvested V crotched cherry (stems binded +- 3 feet) and to my surprise lumber was perfect and with beautiful pattern along the V crotches. Makes you wonder!

From contributor N:
If you have 3 or more stems, should you limit the number of stems cut per growing season? Or is it okay to go ahead and cut all but the crop stem?

From contributor C:
I think professional foresters would agree with me that you may as well cut them all at once. The next year you should have good growth.

As stated, cutting on an angle so the water runs off might help reduce the occurrence of decay.

Harvesting the whole clump is sometimes better, as you get nice figured wood at the crotch. But if the stems are too small, sometimes cutting back to a single stem is the only answer.

Again, worst case scenarios are non decay resistant species, and v crotches are more susceptible to decay than a U shaped crotch. But both v and u shaped crotches make beautiful figured lumber.

From contributor N:
I remember reading somewhere that any time a tree is pruned you should never take more than 1/3 of the crown or you might stunt/hurt it. Seems that trimming the sprouts would be similar, but maybe not since it has already lived through a more drastic pruning, and is probably younger and more vigorous than the 100 year oak in the back yard. Makes sense about cutting to allow for water shed, though.

From contributor C:
I believe that's true - it is hard for the tree to send leaf shoots out of old thick bark. The less leaves to capture sunlight, the less growth will develop.

Multi stemmed tree thinning is a gamble. They will usually lean more and more the larger they get, and we all know leaners generally do not develop good wood (tension wood develops). So with a double stem, for example, cutting one may let the other develop into a tree with more clear, knot-free growth. Then again, decay may occur at the crotch or the cut and the tree will grow slow and may eventually die.

The comments below were added after this Forum discussion was archived as a Knowledge Base article (add your comment).

Comment from contributor M:
I'm unsure about the efficiency of cutting stems at a forty-five degree angle so that water thereby runs off. Assuming a temperate forest with average rainfall of, say, 4 inches per month - including occasional heavy rain for several hours at a time, then any stump will get pretty well saturated over the years.

A forty-five degree cut might forestall the saturation some, but not much, with all that rainfall. This being said, from what I've observed over twenty-five years spent in the woods, most cleanly-cut stumps stay that way, with no unusual rot or resulting disease for the remaining trees in a clump. Healthy trees often sustain significant injuries without long-term harm to the tree as a whole. To be sure, trees get sick, decline, and die all the time, so why not take reasonable precautions (such as following the advice about thinning clumps)?

Trees also can be remarkably resilient, so I wouldn't over-worry about the tree stems that remain after thinning a clump. Rather, I would plan on watching those trees grow, expand, and flourish for many years to come.

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