I know that most of the woody cells in most species of
mature trees have lost their cytoplasm and function only
as physical support, transport, or protective cells. They
are no longer alive in that they no longer have any
metabolic activity. This is true for mature cork as well.

I'm curious to know the percentage of cells in a tree
that are still alive. Or alternatively, what percentage of
a mature tree's mass is composed of living tissue?
I would think that the meristematic tissue, leaves, and
living supportive tissue is a relatively small percentage.

I look out my window at the huge stately trees in my
back yard and I'm curious to know how much of what I
see is alive and how much is scaffolding, pipes and
covering built up over the years by a relatively small
bit of living tissue.

Does anyone know the answer? Educated guesses
and speculations are also welcome (this is, after all, the
Internet

Thanks.

Alan

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.
PvR

"Alan Meyer" schreef in bericht
. ..
I know that most of the woody cells in most species of
mature trees have lost their cytoplasm and function only
as physical support, transport, or protective cells. They
are no longer alive in that they no longer have any
metabolic activity. This is true for mature cork as well.

I'm curious to know the percentage of cells in a tree
that are still alive. Or alternatively, what percentage of
a mature tree's mass is composed of living tissue?
I would think that the meristematic tissue, leaves, and
living supportive tissue is a relatively small percentage.

I look out my window at the huge stately trees in my
back yard and I'm curious to know how much of what I
see is alive and how much is scaffolding, pipes and
covering built up over the years by a relatively small
bit of living tissue.

Does anyone know the answer? Educated guesses
and speculations are also welcome (this is, after all, the
Internet

Thanks.

Alan

"P. van Rijckevorsel" wrote in message
...
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.
PvR

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. I'd think we'd
see a couple of years at the beginning when all cells are
alive, then a gradual decline as the tree grows up and out,
then perhaps a levelling off that lasts for years as the
mature tree lives out its life, then a steady and perhaps
rapid decline.

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

Alan

"Malcolm" wrote in message
...
...
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

"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

P. van Rijckevorsel wrote:
"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





Remember too, that unlike animal cells which are mostly alive, most of
the volume of "living" plant cells is also non-living space -- the cell
wall and middle lamella are non-living, as is the vacuole inside the
cell -- just a big bag of non-living liquid, so that perhaps 80-90% of
each living cell is actually non-living (part of the apoplast). The
symplast -- the truly living portion of the cell, consists just of
cytoplasm and its organelles, and is continuous throughout the plant via
plasmadesmota -- small tubes running across cell walls, linking the
cytoplasm and the plasma membranes of one cell to another. Also inside
a leaf, there is quite a lot of air space -- areas not occupied by
living cells. So if you consider all non-living space in the total
volume of a tree, you end up with quite a lot more than just xylem.

"Malcolm Manners" schreef
Remember too, that unlike animal cells which are mostly alive, most of the
volume of "living" plant cells is also non-living space -- the cell wall
and middle lamella are non-living, as is the vacuole inside the cell --
just a big bag of non-living liquid, so that perhaps 80-90% of each living
cell is actually non-living (part of the apoplast). The symplast -- the
truly living portion of the cell, consists just of cytoplasm and its
organelles, and is continuous throughout the plant via plasmadesmota --
small tubes running across cell walls, linking the cytoplasm and the
plasma membranes of one cell to another. Also inside a leaf, there is
quite a lot of air space -- areas not occupied by living cells. So if you
consider all non-living space in the total volume of a tree, you end up
with quite a lot more than just xylem.

***
Yes, good point. (Although dead cells are not limited to the xylem, and the
xylem is not limited to the wood)
PvR

"Malcolm" wrote in message
...

In article , Alan Meyer
writes
...
Good ideas here. I did a little research on the web and found
that the experts agree with you

Err, well, how nice :-)

My apologies.

I should have said "the _other_ experts agree with you" :^)

Thanks for the reply.