| Characteristics
of Tree Age |
Robert
Leverett |
|
Jul
15, 2002 17:53 PDT |
Ents:
Dale Luthringer's recent question about
the bark characteristics of old
yellow birch remind me of my growth in awareness of the aging
characteristics that accompany various tree species. I was
independently
developing that awareness as others like Lee Frelich, Dave
Stahle , and Ed
Cookwere continuing to hone their already considerable skills.
compared to
their skills, I was a babe in the woods. In the case of Frelich,
Stahle, and
Cook, it was not sufficient to identify old trees, but
recognizing when
trees had likely passed certainly age thresholds, such as 500
years for
eastern hemlock, and 1,000 years for northern white cedar and
bald cypress.
Proceeding on my own, during the late
1980s I began to locate sources
that discussed the maximum ages that had been recorded for
various species.
Charlie Cogbill is one of the scientists who tracks the maximums
and where
they occur. I regard Charlie as the most reliable source of data
on max
ages. However, in those early efforts at understanding the
maximums, I had
no way of qualifying the sources. For example, I read that an
eastern
hemlock in Pennsylvania (I think) had been dated to 988 years.
This was
amazing. The oldest confirmed maximum ages for hemlock were
typically
between 500 and 550 years. Here was one nearly double the
closest maximums.
What was the explanation?
One might expect that a species would
reach its greatest age in a parts
of its range where it receives its best nutrients and is most
free of fungal
attacks and insect pests. However, longevity is often attained
in conditions
of great adversity, such as high, cold, and dry regions, witness
the
bristlecone pine. The swamps of the Southeast are home to bald
cypress that
attain ages of 1,500 years and older. That is hardly high, cold,
and dry. It
is low, warm, and wet. The great hemlock ages attained by Lee
Frelich in the
Porcupine Mountains - cold and wet, are matched by hemlocks in the
Great
Smokies - not as cold and wetter. In addition, the ancient
hemlocks of the
Smokies are giants. Anybody see any patterns? I sure don't. The
black gum
achieves perhaps its greatest ages in the extreme northern part
of its
range - New Hampshire. It comes close to the New Hampshire
maximum in the
southern Appalachians and there is a possibility that a stand in
New Jersey
may contain the largest stand over very old black gums known.
If identifying the conditions that
produce the oldest members of each
species continues to elude us, recognizing age through physical
characteristics does not. But here one must suspend one's
dependence on
numbers - an odd thing for me to say. However, I have been in
the company of
distinguished ecologists who could not recognize aging
characteristics and
some didn't believe age dating by eye could even be in the ball
park. Had
these doubters had to wager with the likes of scientists like Ed
Cook, Dave
Stahle, and Lee Frelich, the latter would have taken the former
to the
cleaners.
Some species show their ages very well
through only a few physical
characteristics such as bark texture and overall physical
symmetry, crown
structure, and root mass development. Hemlock, white pine, sugar
maple,
yellow birch, and black birch all reveal their senior citizen
status very
well through these characteristics. American beech is tougher.
Northern red
oak is intermediate. Sometimes it does show its age clearly and
sometimes it
doesn't. When it does, the characteristics don't deceive though.
Fast
growing species like cottonwood can cause trouble, but still
there are clues
to advanced age. The progression of mature bark up the trunk and
onto the
higher limbs separates 50 year old cottonwoods from those around
100.
What is especially rewarding is when
one's abilities in age recognition
advance to the point that large areas of forest can be placed in
a age class
at a glance. For instance, in western Massachusetts, lots of
trees in the
125 to 175 year age range with a few exceeding 200 years and
none
conspicuously older can signal areas returning from the period
of maximum
clearing - perhaps an old wood lot. So age classes can speak to
past natural
disturbances and human land uses. Putting it all together is a
challenge.
Tom Wessels is especially talented in
seeing the clues to past
disturbances of varying types. He sees broad impacts that I
often miss. But
we see the same aging characteristics in individual trees.
However,
regardless of the confidence we have in ourselves, we need to
take a few
cores to calibrate our eyes to the local site. It was this
approach we used
to qualify large areas on the southern Taconic crest as old
growth and we
haven't even begun to exhaust the old growth acreage. But
without an eye for
individual tree age, we would have passed by this treasure as
have many
others.
How soon can one learn to age date trees
by eye? Well, if you already
know the species, you can make a heck of a lot of progress in a
year. But
realistically it requires several years to get to the point
where you can
make calls with confidence and even then you need to take a few
cores to
calibrate the eye. Of course historical information about a site
is
invaluable. It can make the difference in your confidence level
and can lead
to the avoidance of mistakes, but historical research cannot be
relied on
completely. If this thread proves interesting to the rest of
you, I'll share
some personal examples of where historical accounts of land use
point in the
wrong direction so far as judging the degree of European impact.
Bob |
| Re:
Characteristics of Tree Age |
TJ
Sullivan |
|
Jul
15, 2002 18:51 PDT |
Bob,
I for one, am very interested in determining tree age through
visual
characteristics; as well as recognizing historical disturbances.
Please
continue to share your experiences.
Does red spruce show its age?
I just returned from a patch of the White Mountain National
Forest in
northern NH where much of it had the feel of being heavily
disturbed in the
past. I saw no evidence of recent logging but the predominant
trees seemed to
be paper birch and red maple. There was a fair amount of striped
maple,
serviceberry and mountain maple with a few larger spruce and fir
mixed in.
Most of the red maple looked unhappy and many where dead or
dying. But
amongst this forest where some large and small pockets of older
spruce and
fir with healthy herbaceous layers and a variety of lichens.
The whole forest seemed to be the reverse of what I would
expect, with a
large seemingly perpetual early successional component and
smaller mid to
later successional patches. The one thing I did notice was an
over abundance
of moose sign. Fresh tracks, moose droppings, barked trees and
rubbed trees
were everywhere. There where few smaller fir trees that had not
been heavily
browsed. This area probably has one of the highest densities of
moose of any
place I have seen in VT or NH. I wonder if they are a
significant contributor
to the appearance of this forest.
Now you have me thinking of determining the history of this
forest as well as
the ages of many of these trees. I think you are becoming a bad
influence on
me;-)
Tim |
|