Wednesday, August 12, 2020

Black Birch: Setting the Record Straight

Bob Leverett, co-founder of the Native Tree Society, co-author of The Sierra Club Guide to the Ancient Forests of the Northeast, and co-author of American Forests' champion tree measuring guidelines, has been leading the charge to give the black birch tree proper recognition for the height stature it achieves. The following is an essay penned by Bob.

The Birch Quintet

Lessons in Natural History, Tree-Measuring,

and Ecology with Aesthetic Overtone

by Robert T. Leverett



How is the tree species black birch (Betula lenta) related to classical music? This is a question to which I gave little thought until Monica and I got married and I moved in to share her beautiful home in the woods of Florence, MA, and I do mean in the woods. Monica has a cantilevered music room that is nestled beneath the canopy of a cluster of eastern hemlocks (Tsuga canadensis) and black birches that are located downhill behind the house. The crowns of the birch form a canopy that shades the music room from strong sun. In return, these trees are daily bathed in the mellifluous sounds coming from Monica’s pianos. As a classical pianist and retired professor of music from Smith College, Monica has spent countless hours at her instruments. The non-human beneficiaries of her playing have been the chipmunks, squirrels, songbirds, and an occasional barred owl (perched on a hemlock branch watching for scrumptious little rodents); but most importantly, her trees. I don’t know if trees, and plants in general, actually respond to different musical sounds, but if they do, Monica’s trees get their leaves bathed daily in Mozart, Beethoven, Schubert, Bach, and dozens of other distinguished composers.

How does black birch compare to other species in terms of height? As a dendromorphometrist and co-founder of the Native Tree Society (NTS), I spend my time not only measuring trees, but developing better methods, and testing high-tech instruments. The trees behind our house provide me with a superb outdoor laboratory. The canopy is dominated by exceptionally tall trees, including a white pine (Pinus strobus) now just topping 141 feet. Three tuliptrees (Liriondendron tulipifera) and a second white pine all top 130 feet in height. Northern red oaks (Quercus rubra) make it almost to 120 feet. A lone white ash (Fraxinus americana) touches 113 feet. This, then, is an exceptionally tall private forest for our geographical region. 

But where does a species like black birch, which is usually described as a medium-sized tree reaching from 60 to 80 feet at most in height, fit in? Presumably, the birches fit snugly under the super canopy created by the other species. The prestigious Silvics of North America, the U.S. Forest Service’s bible, states a maximum height of 70 to 80 feet for the black birch, and then, only on the best sites. The U.S. Plant Database lists 60 feet as the species’ mature height. Other sources, often university arboretums, frequently list the maximum height of the species to be 50 to 60 feet. I can tell you reliably that all these sources are wrong, and wrong by a lot. Perhaps this species just isn’t paying attention to the scholarly sources.

I acknowledge that initially I didn’t pay much attention to the cluster of slender birches shading the music room. As we descend the hill behind the house, we must pass between them, as a gateway to the robust pines, tuliptrees, and oaks just beyond. However, at some point, I started noticing these dutiful gate keepers, offering us a pathway into the forest green. Much later I named the cluster of five the “Birch Quintet.” 

The story could have ended there, except from the time I joined Monica in 2006 to the present, those five trees continued to rapidly gain stature, despite their slender trunks (the largest is a mere 4.7 feet around). But despite our seeming indifference, Monica’s “Birch Quintet” refused to be ignored. In addition, I had begun a database on the species. My NTS companions and I proceeded to measure black birch from New Hampshire to Georgia and west to Ohio. I was determined to correct the record on the species, as alluded to above. But surely outstanding members of the species would not be growing just outside Monica’s music room, preferring some distant woodland--or would they?

The Quintet has quietly and gradually crept up into the upper height category for the species, and I am now pleased to announce that one of the five ("Monica's Birch") has just reached a height of 99.0 feet! Please remember, you heard it from me first. But is my claim accurate? Confirming the measurement is a story unto itself and is the focus of the appendix following this essay. 

99-ft Monica's Birch

Notice how Monica's Birch bends eastward to reach the light – and toward the music room. Two other members of the group are also in the photo.

This essay will now look more generally at the dimensions of the black birch being achieved throughout its range and speculate on why it has been so under-measured.

The Black Birch Along Broad Brook and Elsewhere

Of the five members of the “Birch Quintet,” three for certain, and maybe four, reach skyward over 90 feet in height, and the remainder are close behind. However, it turns out that the quintet is in good company. In the swath of forest along the Broad Brook corridor that extends about a mile and a half upstream and a quarter mile downstream behind our house, there are at least a dozen black birches over 90 feet tall. I expect that if we did an intensive search, we’d find 18 to 20. One tree, a half-mile upstream, is named “Schubirch,” after Monica’s favorite composer, Franz Schubert. This outstanding birch is a very impressive 107.5 feet tall as last measured by NTS member Jared Lockwood.

In fact, the birches are so impressive that I hardly pay attention to any growing along the stream corridor just reaching to the 80-foot threshold maximum cited by Silvics. So, given what these outside sources say about the black birch’s stature, is Broad Brook’s contribution exceptional for the species? No, not in the least. We have measured black birch to over 100 feet on more than 25 sites in Massachusetts alone. I expect that number could double. Elsewhere within the range of the species, 100-footers have been confirmed from New York all the way to Georgia and South Carolina. One tree on Long Island reaches a remarkable 121 feet, as measured by NTS member Erik Danielsen. Erik’s measurement is the best we’ve done. The second best is 117 feet, measured by Will Blozan of NTS. That tree grows in the Great Smoky Mountains National Park.

In Massachusetts, Jared Lockwood recently measured a black birch to 111.5 feet in Mohawk Trail State Forest, breaking John Eichholz’s old record of 110.5 feet. In fact, 111.5 is the best we’ve done in New England. This said, I expect that Connecticut, to the south, can easily match Massachusetts with respect to tall black birches. We have spent almost no time measuring the species in the Constitution State.

In Pennsylvania and Ohio, we’ve measured black birch to between 113 and 115 feet tall. And on good growing sites, the species has little trouble reaching heights of from 90 to 105 feet over much, if not most, of its range. We can authoritatively state that the maximum for the species on good sites exceeds 100 feet, though usually not by much.

In the bigger picture, black birch is our 74th tallest eastern species based on our NTS database. So, the species can’t be promoted as a super performer, but one-hundred-foot tall black birches are widely spread and 80–90 feet is quite common in mature forests where that species is present and reasonably abundant.

Still, the “Birch Quintet” remains a small cluster of slender trunks growing outside of Monica’s music room. Most people visiting us hardly notice those trees. At best, they serve as part of a pleasant forested backdrop, visible from our back windows, deck, and patio. They create a kind of soothing natural woodland wallpaper, but without distinction. However, Monica’s Birch, now standing a proud 99 feet tall, reminds us that it and its Quintet members should not be taken lightly.

The next photo shows the largest member of the Quintet, which measures 4.7 feet in circumference at breast height, or 18 inches in diameter. By comparison, Schubirch measures 7.0 feet in girth, and another named Archie is 7.1 feet around. The straight trunk to the left is Monica’s Birch. 

Largest Quintet member



Birch Quintet

Photo "Birch Quintet" shows the trees from above. The rightmost birch has two stems, but is one tree. The big tree with the orange ribbon is Monica’s Pine - the 141-footer mentioned above. A hemlock trunk is in the right foreground; its lower dead branches were trimmed to enhance its aesthetic appeal. 


 Ecology and Beyond

The black birch has simple, serrated leaves that turn a pleasing golden yellow in the fall – arguably the prettiest of the birch family. Branching is upright and alternate. Bark is smooth and gray-black when young, with rows of lenticels plainly visible. 

Young black birch


~130-year-old black birch

Bark on older trees is broken up, first into an irregular vertical pattern, and later into numerous platelets, the sign of advanced age. The species has a number of common names, with black, cherry, sweet, and mahogany birch being the principal ones. The name mahogany probably has several origins. One comes out of the southern Appalachians, where old timers thought they had a species of mahogany growing in the coves. They called it mountain mahogany.


Our New England woodlands are well suited to grow members of the birch family, including white (or canoe) (Betula papyrifera), black, yellow (or silver) (Betula alleghaniensis), gray (Betula populifolia), and river birch (Betula nigra). By the way, river birch is also referred to by some as black birch.

The seeds of the birches are very small and light; they don’t penetrate the leaf layer on the forest floor easily. As a consequence, we commonly find birch seedlings sprouting where the litter layer is thin and mineral soil is exposed, and prolifically on the trunks and tip-up mounds of fallen trees. For the more botanically inclined, black birch is classified as monoecious, meaning that both sexes occur on the same tree. Birch roots can also wrap themselves around rocks in an octopus-like embrace. The effect can create a kind of Tolkienesque woodland.

Black birch is a heavy wood. Its green weight of 65 lbs per cubic foot (ft3), exceeds that of yellow and white birch, and is about the same as N. red oak and most of the hickories. Its oven-dried weight is 41 lbs/ft3. It literally is no lightweight.

Black birch has a distinguished cultural past. From its sap, birch beer has been brewed. With age, the wood of the species looks like mahogany. It burns well as firewood. In recent years it fell out of favor with lumbermen, but I think it is now rebounding. In the past, I heard some lumbermen refer to black birch as a “trash tree,” a regrettably insensitive and utterly uninformed way of thinking about a naturally occurring and ecologically important species. 

Black Birch Burl lamp





Our birch trees are around 100 years old, maybe a little older, which means they likely started growing during World War I. In human terms, they would be very old, but in birch terms, they still have lots of life left. Black birches can easily live past 200 years, and have been dated to as old as 368 years. The oldest birch we know of in Massachusetts is now approaching 350 years, and Ray Asselin and I have dated many to over 200 years, with one almost 300 years old.

Those tackling the following appendix will recognize that confirming the height of Monica’s Birch was a lot of work for me-- fun work-- but work, nonetheless. Still, it’s what I do in retirement. Such fussiness over decimal places isn’t necessary for the vast majority of forest workers. In fact, the amount of work that accurately measuring a tree like Monica’s Birch requires, eliminates the method in the appendix as a useful technique for forestry professionals who live off of quick results. Timber cruisers can’t afford the time that members of the Native Tree Society devote to achieving the highest degree of accuracy that their instruments allow. But there is a price for the loss of accuracy. The public cannot trust traditional sources like Silvics of North America and the USDA Plant Database to provide accurate species maximums.

I will now close the main essay by suggesting an experiment for the imagination. As you look at the photos, imagine for a moment Monica sitting at her piano playing the New England composer Amy Beach’s composition Young Birches. True, the Beach piece is most likely about young white birches, or if not, then yellow - Thoreau’s favorite of the three. However, the Quintet is composed of older black birches. All three birch species, black, yellow, and white, grow together along the Broad Brook corridor, and do so coexisting peaceably. Black, yellow, and white living in harmony - a lesson for us humans …… Shhh, everyone, Monica has begun to play. 


For a delightful film on birches, see New England Forests' "Birch, Sweet Birch: New England’s Forest Birches".

Appendix - Measuring Monica’s Birch (an engineering nerd’s favorite retirement pastime)

The traditional forestry technique for measuring tree height uses a tape commonly either 66 or 100 feet long, and a device called a clinometer, of which there are several kinds, but one has a scale that reads height of an object as a percent of a level baseline. This is a convenient tool because if the baseline is exactly 100 feet, then the percentage read directly from the scale is the height. For example, if the baseline is 100 feet and the percentage display reads 70, then there is 70 feet of the tree’s height above eye level. Were the baseline, say, 75 feet, then the height would be 75 x 0.75 = 56.3 feet.

After getting height above eye level, turning the instrument toward the base of the tree and taking a reading gives the part of the tree’s height that is below eye level. Then adding the two results gives the full height of the tree – supposedly. However, this method carries the assumption that the base of the tree, the end of the base line, and the top being measured are all in vertical alignment. This is often close for young conifers growing in a stand on level ground, but for older trees, especially hardwoods grown in a stand and on uneven ground, the verticality requirement is frequently not met. If the measurer is too close to the trunk, the top is often not visible and what is mistaken for the top is the end of an upturned branch that is closer horizontally to the measurer than the baseline. This leads to an estimate that is too high.

More could be said here, but suffice it to say that clinometer measurements are seldom satisfactory in a closed canopy forest. This applies equally to the automated hypsometer equivalent that often is labeled as a tree-height routine. However, with modern laser rangefinders and their hypsometer equivalents, the distance to the top of a tree can be measured directly. This distance represents the hypotenuse of a right triangle, and, along with the angle taken to the top, allows the measurer to calculate the vertical separation between top and eye using the trigonometric sine function. The trunk and a level baseline to it at eye level is not required. Taking the distance and angle from the same location to the base gives the vertical separation between eye and base. Adding these two components of height together gives total tree height. This is called the Sine Method. The tape and clinometer technique is called the Tangent Method. With the Sine Method, the measurer can measure tree height to within the accuracy limits of the equipment, avoiding the pitfalls of the Tangent Method. Both these measuring techniques are built into most laser hypsometers.

The top and base of what I call Monica’s Birch cannot be seen from a single location. This is frequently the case for trees growing in close proximity to one another. What happens if the top and base of the tree being measured are not concurrently visible from any location? We must turn to a surveying method to measure height in stages. This is how Monica’ Birch was measured.

I first located a spot where I could see the top of the birch. From there I could see downhill to the trunk of a honey locust. From a chosen spot on the trunk at near eye level when standing next to the trunk, I could see the base of the tree and a marker that I had put on it. I had to work my way around part of the house to get from top to base.

From my first spot, I shot the top of the birch with an LTI TruPoint 200h laser rangefinder. The TruPoint has both class 1 and class 2 lasers. Each shot returns the most accurate reading it can obtain. If the shot is from the class 2 laser, the answer is to three decimal places. If from the class 1 infrared laser, the return is to two decimal places. As can be seen in photo 1, the direct slope distance from instrument to target was 120.81 feet. The vertical distance was 73.81 feet.

Photo 1

 So, from where I took that measurement, I had accounted for 73.81 feet of the vertical separation between top and base. Note that the distances are to two decimal places meaning that the infrared laser had to be used. 


 I swiveled my tripod and aimed at the target downhill on the honey locust, and measured the additional vertical separation down to that point. Photo 2 shows the result. 


Photo 2

 The center of the target on the honey locust tree was 6.024 feet below instrument level. The minus sign indicates below instrument level. Therefore, from the top of the birch down to the level of the target on the honey locust was a vertical separation of 73.81 + 6.024 = 79.834 feet.

Next, I moved down to the honey locust target, placed my TruPoint against the center of the target, pointed it down to the target on the base of the birch, and shot that target. Photo 3 shows the TruPoint’s display.



As can be seen, the vertical distance to the center of the base target was -18.875 feet. This gave a total of 79.834 + 18.875 = 98.709 feet of vertical separation between top and the center of the base target. I then went to the base with a yard stick. I had placed the base target at a visible point from the honey locust target. The center of the base target was 3.5 inches above ground level at the mid-point of the base. So, adding another 0.292 inches gave a total tree height of 99.001 feet. An even 99 is close enough. On Aug 8, 2020, I performed the measurements again and came out with 98.985 feet. I’ll stay with an even 99 feet.

The above measurements were all done using my LTI TruPoint 200h, which I affectionately named Mini-Me. However, I have other instruments and decided to use my Impulse 200LR (named Sasquatch) as a check. The result came out to 98.75 feet. So, we have now three results: 99.001, 98.985, and 98.75. Not wanting to leave any instrument out, next, I used my TruPulse 200X (named Sparky), and got a height of 99.05 feet. So, now that we have four independent measurements of Monica’s Birch averaging 98.94
feet, I suppose it becomes an honorary 99. 

Ah, but I still wasn’t satisfied. I had my Nikon Forestry Pro. Using it, I got 74.5 + 7.0 + 19.5 = 101.0 feet. Alas, the Forestry Pro is not as reliable as the LTI instruments, because for the crown shot, I got numbers ranging from 73.5 to 75.5. The 74.5 was, conveniently, the average of the extremes. The average of the 4 instruments yields 99.4 feet. Still, how tempting it is for me to conclude that Monica’s Birch is 100 feet. However, averaging a mix of measurements from more accurate instruments with those of less accuracy is not the best strategy. So, I had to have at least one more set of measurements from a more accurate instrument. So, on August 12th, I headed out again with the Impulse laser. My measurements came to 73.52 + 6.66 + 18.53 + 0.29 = 99.0. Going once. Going twice. Going three times. SOLD!