"P. van Rijckevorsel" wrote
The answer is very simple when a tree just starts out, after germination,
all of its cells (100%) are alive. As it grows bigger and bigger, every
year the percentage of living cells drops. It only reaches zero when
the tree is truly and completely dead.

From: "Alan Meyer"
Thanks, but I wonder if it's really that simple.

If we plot a curve of living cells to total cells I bet we
wouldn't see anything approaching a straight line going
from 100% to 0% over the life of the tree.

***
No indeed, there will be nothing like a straight line.
Measuring every year at the same time will result in a inverse s-shaped
curve, broken at the end by whatever kills the tree.
* * *

I'd think we'd
see a couple of years at the beginning when all cells are
alive,

***
No. There will be dead cells pretty quickly
* * *

then a gradual decline as the tree grows up and out,
then perhaps a levelling off that lasts

***
basically till the end
* * *

for years as the
mature tree lives out its life, then a steady and perhaps
rapid decline.

***
That will depend entirely on what kills the tree
PvR
* * *

I'm particularly interested in that middle, mature period
when the tree has achieved its growth but is still very
viable.

Alan