Characteristics of Tree Age    Robert Leverett
   Jul 15, 2002 17:53 PDT 

    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

    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

    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.

Re: Characteristics of Tree Age    TJ Sullivan
   Jul 15, 2002 18:51 PDT 

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