I understand that (in the UK at least) yield class is the amount of
biomass created per annum - eg. YC12 means 12 cubic metres/year/hectare.
What exactly does this include - is it the total biomass including all
the foliage and/or branches or does it refer to the economically useful
Ps. How much of a tree is ecomically useable as say sawtimber? I realise
this is a broad question, but are there any rules of thumb?
For example, what percentage of an 18 inch white oak might be utilised
as plank/fencing material? 50 per cent or substantially less?