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.
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.
Many of our second growth forests regenerate through stump sprouts.
Lloyd Casey, forum technical advisor
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.
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
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.
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.
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.
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.