Journeys in ancient and old growth forests

Recognizing old trees

Black Gum, 510 years Photo: Nate Torenvliet
Black Gum, 510 years old. Photo: Nate Torenvliet

I recently received an email about a 510-year-old Black Gum tree growing behind an archery club in Niagara Falls. Nate Torenvliet, an arborist and amateur old-growth sleuth, had found the tree, drilled out a tree core (a pencil-shaped section of wood), and counted 498 annual growth rings. Another tree nearby was more than 400 years old. This unassuming woodlot in a relatively populated agricultural area was first identified in 2003 by the late Bruce Kershner, an old-growth researcher from New York State who estimated that the Black Gums there were 300 to 450 years old.

Kershner had stirred up some controversy by claiming to be able to estimate tree ages based on visual characteristics, a claim that was denounced by some academics, and largely ignored by many others. Kershner made some fairly bold age claims in Ontario that were likely to raise eyebrows, but Torenvliet’s confirmation of one of the more extreme age estimates seems to be at least a partial vindication for Kershner, even though he’s not around to hear of it.

In any case, the science of recognizing old age based on visual characteristics has been maturing of late, as dendrochronologists (who use tree growth rings to study past changes in climate) have learned to recognize old trees for tree coring; finding the oldest trees in the forest with visual cues can save them a lot of time that would be wasted coring younger trees. An article by Neil Pederson on recognizing old trees appeared in the Natural Areas Journal in 2010, which was inspired by the observations of many dendrochronologists since the 1970’s; and it helps legitimize many of the visual cues Kershner and Leverett describe in their Guide to the Ancient Forests of the Northeast or that we describe in Ontario’s Old-Growth Forests.

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A trunk with very little taper, and large branches very high on the tree, are signs of old age

You too can learn these characteristics. Maybe there’s a tree in your local forest that you’ve always suspected was old, but didn’t know any way to find out. It’s important to point out that the only way to accurately age a tree is to drill a tree core from the trunk and count annual growth rings. But it’s possible, with practice, to make a reasonable guess at whether a tree is old, without doing anything invasive. How can you practice? Go to known old-growth forests and look at trees. Or use trees cut from trails as an opportunity to count annual growth rings. But let’s back up for a minute and talk about the visual cues that you’re looking for.

First of all, forget about size. A big tree might be half the age of a much smaller tree nearby. Using size to age trees is only slightly more reliable than using size to age people; after an initial growth spurt (generally less than 20 years for people, or  around 100-150 for trees) it doesn’t necessarily change that much. True, trees will continue to gain diameter (as do many people) but it may be less than a millimeter per year in some cases. Just to make it more complicated, shade tolerant trees may never have the initial growth spurt, and can grow very slowly under the forest canopy for centuries, remaining quite small. Hemlock is the master of this; big-tree hunter Will Blozan reported finding a 400 year old hemlock that was only 18.6 cm (a little over 7 inches) diameter. But while old trees may grow slowly, the shape of the trunk and branches change as trees age, and so does the bark. Some of the characteristics you should be looking for include:

The trunk has very little taper

We’re used to seeing trunks that taper to a young, growing tip – but trees attain most of their final height within 100 years, and the trunk starts to grow along its whole length after that. In fact diameter growth is fastest near the top of the trunk – so over time the trunk looks more and more column-like as the tree ages.

The trunk may develop spirals, or buttresses; it might develop curves or changes of angle over the length of the bole, like the curved spine of an old man.

1840 illustrations by Philip Henry Gosse showing characteristics of an old-growth elm tree
1840 illustrations by Philip Henry Gosse showing characteristics of an old-growth elm tree

Branches are large, sparse, and clustered at the treetop

Old growth trees are sometimes compared to celery stalks. The celery analogy is meant to illustrate that old trees have tall thick trunks with relatively few branches, and little foliage, clustered at the top. The main difference would be that on old growth trees the branches would often be proportionally larger than the celery branches (also they are harder on the teeth, and not as complementary with cream cheese).

Remember that branches of very old trees may have been growing for hundreds of years in their own right, and are essentially small trunks themselves. Odd twists that seemed innocuous when the branches were small become magnified as trees age, and periodic damage from ice or wind can reshape the branches in bizarre ways that persist potentially for centuries.

Tree bark changes

Tree bark can be a very good indicator of age, but is highly variable by species. Generally, most hardwood species become increasingly ridged or plated until they reach early middle-age; then as they become truly old the bark begins balding. However Beech may hardly change at all, while Yellow Birch becomes increasingly more plated for centuries before showing signs of balding (and even then, never approaches the smooth bark of its youth). Conifers tend not to show balding, and are highly variable. White pine trees grow increasingly ridged, red pine bark becomes beautifully puzzled and develops some ridging.

The ancient cliff-growing trees

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Ancient Bristlecone Pines

Ancient cliff-dwelling cedars, and other dwarfed trees, can be found almost anywhere in North America, and may measure their ages in millenia. The oldest living cedars in Ontario are over 1300 years old. The oldest known living trees in the world are the Bristlecone Pines of California and Nevada, which can live to be over 5000 years old. These trees share similar characteristics of growing in harsh, relatively rocky environments, and being able to continue growing when parts of the trunk die. It gives them a distinctive bonsai  sort of look. Dwarfed ancient trees, growing on cliffs or rocky slopes, are probably more widespread than most people realize. Doug Larson, a scientist at the University of Guelph and prominent researcher of ancient cedars, travelled through the United States in 1997 looking for examples of old cliff-dwelling trees. “I went to 15 different states,” he recalled, “and within a couple of days of sampling in each state we’d found the most ancient forest known for those states – for every one of them.”

Visual cues for recognizing ancient cedars, and other dwarfed trees, are different from those that are useful with forest-dwelling trees. Here’s a summary, excerpted from Ontario’s Old-Growth Forests:

Some features of ancient cedars (excerpt from Ontario’s Old-Growth Forests):

  • Isolation: These trees reach tremendous ages partly because they are growing slowly in places where forest fires can’t burn, usually isolated by lots of rock. Anywhere that you see a dwarf cedar tree totally exposed on a cliff, rocky outcrop, talus slope, or small island, it has potential to be older than you’d expect.
  • Partly dead: Over the centuries, parts of these cedars will die while other parts keep growing. It is not unusual for the main axis of the tree to die, and side branches to become dominant, which over time leads to some of the bizarre shapes that can be found in ancient cedars. Typically, at least half of the tree will be dead within the first few hundred years that it is growing, and this process often continues, so that the amount of dead wood may give some indication of old age.
  • Strangely shaped trunk: Ancient cedar trunks often start to grow unevenly, in one or more strips of growth. This kind of growth usually happens very slowly, so extreme unevenness of the trunk often means extreme old-age.
  • Size: Size doesn’t mean much with cedars – the slowest growing tree ever recorded is an eastern white cedar which was 155 years old but was only 1.5 cm in diameter. It weighed 11 grams, about the same as a AAA battery. One cedar at Lion’s Head was only 14 cm across at the base, and 225 cm long – as Pete Kelly and Doug Larson put it, “even though this cedar could fit in the trunk of a car, it is 793 years old.” On the other hand, a 1,033 year-old cedar growing on the talus slope at the base of Lion’s Head was 75 cm in diameter at the base and 10.5 metres tall. These large old cedars are found where there is more soil for them to put their roots into, such as at the cliff edge, large fractures in the cliff-face, or in talus slopes at the base of cliffs. Old cedars often have trunks that are fat at the base but are extremely tapered – the opposite of many other old, forest-grown conifers, which become more columnar in shape as they age.
  • Other strange habits: Old trees on cliffs will often grow hanging down the cliff face, so that the roots are the highest point on the tree. However, some of the oldest trees also grow upright. Spiral growth of the trunk is also fairly common in old trees.

 

We maintain a list of Ontario’s oldest trees, and we’re always on the lookout for old trees that have been accurately aged.


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5 Responses to Recognizing old trees

  1. I have read your book which you kindly autographed for me at McMichael gallery a couple of years back. I am writing this because I am on my way to Niagara this weekend and I am interested in the old gum trees. I will look for the archery club. Thanks.

  2. Hello,

    I recently visited Bruce Peninsula and visited this site and read up on the age of ancient cedars. I now realize there are very small and distorted cedars on a vertical rock face overlooking the lake near our cottage near Notre dame du laus. I presume they might be very old. I could make some photos and would be interested for a referral and comments about these trees in Quebec,

    Thank you,

    Marco van der Kooij

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