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I've observed this since the late 1970s at my own parent's property before being in this biz. Later, country clubs, university campuses, and residences. The trend appears to favor deadwood removal.
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Deadwood comes down eventually, with us or without us. I'd prefer not to be hit in the head with a dead limb, then again, in sudden limb drop. we have the risk of being hit in the head with a live limb. If I survive either encounter, I'm not sure what difference it would have made about the vital signs of my attacking limb.
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In short, deadwood removal can have some noticeable benefits as opposed to leaving it.
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I agree, but the original question was still about finding any proofs that the deadwooding had a biological benefit for the tree.
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1. Deadwood does cause shading. In some conifers like Douglas fir, when deadwood is removed, it allows more indirect light to reach interior foliage, reducing tissue death of interior needles and twigs. This can enable the retention of some lower limbs for a longer period of time, and for some homeowners, that is very desireable.
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Again, there are different benefits for different reasons and however deadwood comes down, by time or by us, it can allow for more light beneath the dead limb. In the deciduous trees, the shading was from leaves can be considerably more dense than from just the limb and once dead, those leaves do not return. In context, many conifers live with significant self-shading anyway.
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2. As long as a dead limb is attached, the tree's tissue cannot encapsulate the point of decaying attachment. But once a dead limb is removed, the tree almost immediately starts to encapsulate the spot with new and stronger tissue, which provides a stronger area on the trunk than waiting for a limb to fall off.
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I very much disagree. The expansion of the branch bark collar at the location of the dead limb is singularly the result of the flow of trunk vessels around the intersection of the dead limb. With both cylinders alive, each contributed to the interweave at the junction. The flow of vessels of the parent cylinder around the dead cylinder is not triggered by the removal of interfering deadwood, it occurs as the remaining part of an ordinary process of vessel placement in the continuity of vessels running from above to the areas below.
At some future time, that location is overreached by the expanding girth of the trunk or the parent cylinder, and issues of strength have no particular significance.
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3. Removal of deadwood allows more light to reach understory plants, improving the overall habitat for other landscape plant material.
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We need to be careful in assuming that we know better about the understory needs in general circumstances. In what we would call forests, trees create their own habitats ranging from poisoning the soils against interlopers, to the undisturbed decomposition of forest products that go back many years.
In any case, available light with a group of trees is often vigorously exploited from nearby trees and after a short time, and once successful, new leaves and needles become the new shade.
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4. Deadwood interferes with visual inspection of a tree's interior, as well as access for pruning. So often, I find neglected problems in trees, where deadwood impeded a view of the problem.
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We are again talking here about maintained areas, and yes I guess that there might be some interference for inspections by the positioning of some deadwood. Again, we are still looking for biological benefits from deadwooding.
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5. Deadwood is an obstacle for wind to tug on. And also out here near Portland, especially the east side where the Columbia River Gorge dumps cold air into the rainy city, deadwood accumulates that much more freezing rain weight in the form of ice. So deadwood can increase breakage in our area.
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I also think that deadwood is more vulnerable to wind in part because it lacks the flexibility of a living limb, but ice takes down what it can, liveing or dead, and that has been going on ever since we had trees and ice.
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I don't think deadwooding is always neccessary. But in-general, I find that it provides improvements for urban and landscape needs that are outstanding compared to ignoring deadwood.
Seems that deadwood removal would also be premium for top grade lumber production too. Even pre-deadwood removal.
Some things just seem to work better for our urban needs with man-made improvements. Consider an apple tree. If we let one grow unchecked, the fruit would be near unreachable, disease would increase, more yellow jackets would swarm fallen smashed fruit, etc.. Just one of many examples that man-made hort improvements fit our urban needs.
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I agree that in urban settings there are side benefits to deadwood removal. I don't disagree with man-made improvements and expansions of the value and care, but I don't find any persuasive quality to your observations about the biological benefits like accelerated encapsulation, or as others have said the removal of fungal food.
I have apple trees in Nova Scotia that are untouched, unpruned, and undeadooded. I don't place the expectations on them as fruit producers or want them to be convenient for me. They grow; I watch; they move on, and I wander away. Seems perfectly fine for all of us.
I guess I prefer is to keep things in the proper boxes. Urban settings have different expectations and explanations. The biology of trees spans whatever context of placement and purpose we might assign to trees.
We wouldn't have this conversation if we didn't have chain saws and we didn't provide the product of wood on the ground, living or dead.
Bob Wulkowicz
