Only a thousand years ....give or take

[Khriss]

...don't get him started..... K

[Vespasian]

1 hour ago, daltontrees said:

It' got to be quite a complex phenomenon. Hollowing of the stem will make the weight pressure on the remaining wood greater per m2, except that the crowns have usually retrenched by then and the whole thing weights afraction of its mature weight. Easy calculation if I could be bothered. But it would be interesting to see if new increments in late mature oak revert to ring porous as young retrenchment growth becomes the only foliage in the crown. Another factor might be the recycling of nutrients as a tree hollows out. For the first 500 years an oak might just be taking from the soil, but of the next 500 (give or take) it has 500 years of steadily decaying wood inside it feeding all those nutrients back into the soil. That's a pretty good pension.

My theory involves the loss of weight bearing down to mean the trunk might expand in some way as it hasn't the need to support the previous weight that it had..

 

You could test this theory out..  find two tree's of similar age an size close by to each other, pollard one and take measurements thereafter of both tree's trunks..  see if over the span of a few years the pollarded  trunk hasn't gained some measurable girth on the unpollarded tree..

[tree-fancier123]

17 minutes ago, Vespasian said:

You could test this theory out..  find two tree's of similar age an size close by to each other, pollard one and take measurements thereafter of both tree's trunks..  see if over the span of a few years the pollarded  trunk hasn't gained some measurable girth on the unpollarded tree..

From what I've seen of it - exactly the opposite is observed. An avenue of pollards the trunks will be nowhere near as big diameter as similar age open grown specimens. The compression relief from pollarding is less of a factor than loss of photosynthetic area - the biomolecules that comprise the sapwood growth rings are mostly from the leaves.