Hi, GW Patton,
Trees are excellent organisms to consider with regard to your
question. For one thing, a great part of the young tree is contained
within the old tree, buried under layers of newer wood. Even a tree whose
bole is clear because it has shed its earlier branches still contains
within it the traces of branches (i.e., knots) that tell when and where
they were initiated and lost.
Even without cutting into the wood, one can learn from trees much of
the history of their environment. For instance, a tree growing in the open
will typically have a broad, spreading crown (like a tree left in a meadow
to provide shade for cows). If the meadow is abandoned for grazing, the
progeny of that tree (and others) will grow into a dense second-growth
forest. Now the spreading-crowned meadow tree finds itself surrounded by
and soon out-topped by its tall, slender progeny. The response, in trees
with sufficient plasticity (which is most), is to put up tall, vertical
stems off of the largely horizontal, spreading branches, resulting in a
candelabra -like form that will be recognizable for decades in the forest.
Tree form also reveals the logging history of a forest stand. Many
years after a forest is logged species such as oaks, that produce stump
sprouts, will present not as scattered individuals, but rather as groups of
two, three, or four closely spaced trunks, which are the surviving sprouts
of the parent stump, and are of course, in genetic terms, still the
original tree. These clustered trunks will have few and small branches
directed into the center of the group and will have most of their branches
pointing outward, together forming a complete crown.
Trees show land-use changes in many ways. When a road cut is put
through a forest, species that don't re-sprout well, such as pines, will
show a long, clear boles, very different from the form a pine would achieve
if it grew from seed at the edge of a clearing. Trees that DO sprout well
will put new branches into the new clearing, but it will be obvious that
these are secondary branches because they will be initially small compared
to the mature branches higher up in the crown. Cutting into the tree will
show that the knots of these branches do not extend all the way into the
center of the tree, but rather originate in the growth ring of the year of
the clearing event, or a little later.
Trees growing on wind-swept ridges show a flag-form, with most of the
branches pointing down-wind, and trees in salt-spray zones are "pruned" to
air-foil shapes reflecting the prevailing winds..
Examining individual twigs tells much about the recent history of a
tree's environment. By measuring the distance between bud-scale scares one
can learn how much the shoot has grown over many years. This record is
reliable until the bud-scale scars become unrecognisable due to radial
expansion of the shoot. For an axis that is producing short extensions and
little diameter growth, the scars may be countable for up to thirty or more
years. One will sometimes see a switch to producing long extensions,
probably reflecting some change in the immediate environment, such as the
death of a nearby branch, letting in more light that stimulates growth.
Occasionally, such an axis will revert to producing short extensions,
probably reflecting the growth response of surrounding branches closing the
temporary light gap.
For most common temperate-zone tree species the normal growth habit is
to produce rather straight twigs. When one sees twisted, gnarly branches,
typically in mature trees that are no longer growing vigorously, this
reflects bud mortality. Every twist or turn in the branch is caused by the
terminal bud having died (from insect damage, fungal attack, freezing,
squirrel bites, etc.), de-repressing a near-by (basipetally) axillary bud,
which changes the direction of extension until another tip die-back sends
another bud off in a new direction. As the branch thickens the details of
these mortality evens are not visible on the surface, but careful
dissection with a sharp chisel reveals them buried in the wood.
Hey, I could go on and on, but I hope all this addresses the question
you raised.
Martin M. Meiss
2015-12-08 12:56 GMT-05:00 geepee437 . <[email protected]>:
> Dear ECOLOGGERS:
>
> Apologies for maybe waxing a bit too poetic here but I used to use
> cellular responses as a way to detect and measure stressors. Looking out my
> window, I now see trees with that same world view and wonder "How are trees
> (or any organism's) forms informing us?" What I see (and it doesn't really
> matter where or what they are) are odd forkings, broken spars, and twisted
> limbs. To what degree can the shapes of living things tell us about their
> life and ecosystem?
>
> Just wondering what literature there might be or what your thoughts are if
> you've pondered such things yourself.
>
> Cordially yours,
> GW Patton
> Silver Spring, MD.
>
