"Malcolm" wrote in message
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I've always understood that, in a healthy tree without dead branches, etc., it is just
the heart wood which comprises the dead cells, the rest is still living. And you can
only measure the extent of the heart wood in a living tree by taking core samples.

Good ideas here. I did a little research on the web and found
that the experts agree with you (I hadn't thought to look up
"sap wood" and "heart wood" before.) I also found that the
percentage of sap wood to total wood averages 25-30% in
commercial logs, but is higher in young trees and lower in
older ones.

I believe the cork, i.e., the outer bark, is also dead.

I suspect that at least some of the sapwood is also dead.
As I recall, mature xylem is composed of dead cells whereas
mature phloem has living cells.

Maybe someone has some more ideas to progress further
with this.

Thanks.

Alan