Re: This brings up an interesting question
This all depends upon justification for the work. The original post was talking about the justification because of age. Some old trees are important ecological sanctuarys as well their ability to cheat death and being impressive to our psyche - why end its life when it can be helped? These simple facts are normally complicated because of aesthetics & safety issues.
If the tree has lost its top and is surviving, it can be artificially aided by us by judicial pruning on a regular basis to help prevent heavy regrowth from breaking out and causing an injury to people, property and the tree's amenity. The resulting wounds and decay are beneficial to wildlife.
This is not to be confused with topping or reduction work in an urban environment without justification, and topping should not be confused with ornamental pollarding.
Little of what we do pruning wise is good for the tree. We aren't trying to help the tree - we are compromising the tree for our benefit:
-Increased safety
- Increased light
- Decreasing pavement cracks
All this whilst trying to maintain tree health, safety and amenity within an acceptable level, again for our benefit. If we don't prune the trees to the best of our knowledge, they will suffer a premature death through our hands as an unacceptable risk, or through disease.
So, by that reasoning, we need to retain urban trees to support wildlife, decrease pollution and soften the psycological effects of hard landscapes, for OUR benefit. Both individual Urban & wildland trees may also have sentimental value, that jsutifies their retention in the eyes of the client (In the UK one local authority trys hard to retain a tree that took the crash of Mark Bolan that killed him, because memebers of the public (his fans) identify it as a link to him!), and ecological value that justifies their retention.
You cannot generalise - it depends upon each indidvidual specimen, its genetic capability to withstand certain types of pruning, and the justification for the pruning based upon the needs of the client, the needs of the tree and that of the surrounding environment (amenity/ecology).
From my point of view, if the tree has not yet reached a static mass/dynamic mass ratio of 1:1, then it should be treated (pruned) in such a way as to maintain its natural form, as promoted by most arborists and organisations. If the client wants it down and it won't be missed in the overall landscape effect, fine. If they want it down and little else is around of that stature, or want it topped or reduced for aesthetics, not so fine (I do believe that we are only custodians of the future landscape, and therefore shouldn't be allowed unreasonable behaviour that would take away something to be shared by many others).
If the tree has passed beyond this ratio into senility, then the rule book changes. It all depends upon sentimental or ecological reasons for keeping a tree alive, or both.
The last word on reducing height: Senile trees of low height and large girth are better able to withstand high wind loads, are of ecological importance (that includes us) and impress our psyche with what seems to be the ability to live forever. So what if that means it doesn't look like a typical tree - it doesn't mean all trees should look like that. If we neglected all urban trees to ecological warfare, nature would take our garden away from us. To keep all trees safe, we would have to reduce and pollard them. I wouldn't want a city full of pollarded trees - the system would be reversed and a normal tree would be the exception! We need to appreciate the wonder of old & ancient trees, and identify individuals suitable for this role in the future!
There are no right and wrong answers, only honourable intentions. Variety is the spice of life!
I'll try again-
