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Trees sitting in depressions
On 7 Oct 1996, Vicki Elberfeld wrote:
> What got me thinking about this was the realization that trees
> don't seem to form the bulk of their substance from what they get
> from the soil. If they did, you'd expect them to be sitting in
> depressions. Instead, the soil around them actually seems to rise
> up a little. Then I realized that they could do quite a bit of
> building with just the elements found in air and water. If that's
> true then it's natural to ask whether decay reverses the process.
> Thinking about it, I guess that pretty much has to be what happens,
> but I never hear anyone phrase it quite like that.
From what I have seen you are wrong about this. While the soil
immediately around the trunk of the tree may seem a bit higher, the larger
area encompassed by its roots is always lower. This depression effect is
obvious if you think about how often you see tree roots above the level of
the soil. They must have been below the soil level when they grew there.
The sinking of the soil is spread out over a large area and happens very
slowly so it is generaly not perceivable, but it does occur. A prime
example is right here in our back yard. My lady's great-grandfather built
this house. Seventy-five years ago he planted a cotton wood in the back
yard which still stands. The tree is now more than 5' in diameter and its
branches not only cover our house but extend across the rooves of three
neighboring houses. There is also a Maple in the yard that is about 50
years old. There is clear evidence that the soil level in the back yard
is now nearly 6" lower than it was when the house was built. It is not an
issue of soil errosion as the neighboring yards on all sides are several
inches higher, so the only answer is something has taken the soil from the
middle, obviously it has gone up these two great trees. This indicates
that this is occuring at an average rate of less than one inch per decade.
Quite easy to see why this would be inperceivable because how many
instances are there where you have a trees several decades old and
something around them to measure the soil level over several decades by?
Brian Petroski
Just your stereotypical
polysexual,
bisexual
solitary pagan
from St. Paul, Minnesota
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