On September 11, 2010, the Bob Dunning Memorial Bridge was constructed in true barn-raising fashion. The bridge is a key feature of Pondicherry Park in downtown Bridgton.

Bob Dunning, who died suddenly, was a builder, an artist, and among other things, a teacher–sharing his craft with students young and old.

To honor Bob, who treasured traditional building techniques, his friends and fellow craftsmen designed and built a covered bridge leading into the park.

“As the poet said, ‘Only God can make a tree’–probably because it’s so hard to figure out how to get the bark on.” ~Woody Allen

One of the unique things about the bridge is that each tie beam comes from a different tree species, with the bark left on. As I walk across the bridge, my eyes are always drawn to the beams.

Until I took the Maine Master Naturalist class, I recognized only a few species by their bark. But my eyes were opened to the fact that each species has its own presentation, which is true for everything in the natural world. I wanted to know all of them so I set out to teach myself, beginning with the species on the bridge. These became the focus of my capstone project for the class. I spent hours upon hours pouring over reference books such as BARK by Michael Wojtech, The Tree Identification Book by George Symonds, Manual of Trees of North America by Charles Sargent and Forest Trees of Maine by The Maine Forest Service.

I sat in front of trees and sketched them, trying to gain a better grasp of their nuances. I dragged foresters into the field and picked their brains. And I drove hiking companions crazy as I tried to point out clues.

The result was a brochure that you can pick up at the kiosk (let me know if you can’t find a copy) and a powerpoint presentation that breaks down the species by types of bark. Did you know that there are seven types of bark? I learned that from Wojtech’s book and it made it easier to note the differences.

Follow me now, as I take you across the bridge and give you a glimpse of each tree. We’ll begin on the east side (closest to Renys) and work our way west.

Beam #1: Black Cherry (Prunus serotina): Scales; gray-brown to almost black; small, rough scales randomly placed; curled outward like burnt cornflakes or potato chips.

Beam #2: Yellow Birch (Betula alleghaniensis): Peeling/Curling; bronze to yellowish-gray; curls away horizontally into thin, papery strips; shaggy appearance.

Beam #3: Red Maple (Acer rubrum): Vertical Strips; light to dark gray; almost smooth or cracked vertical, plate-like strips; curls outward on either side; sometimes bull’s eye target caused by fungi.

Beam #4: American Basswood (Tilia americana): Ridges; gray to brown; flattened, square-like ridges with parallel edges; may intersect like a woven basket every 6-12 inches.

Beam #5: Northern Red Oak (Quercus rubra): Ridges and Furrows; light colored, with rusty red inner bark; wide, flat-topped ridges run vertically parallel like ski tracks; dark, shallow furrows separate ridges.

Beam #6: Eastern Hemlock (Tsuga canadensis): Scales; cinnamon-red to gray; rounded or irregularly-shaped scales; inner bark has purplish tint.

Beam #7: American Beech (Fagus grandifolia): Smooth/Unbroken; silver-gray or grayish-green; sometimes blotched with lichen; carved initials remain visible forever; often pockmarks caused by fungi.

Beam #8: White Ash (Fraximus americana): Ridges and Furrows; ashy-gray to brown; intersecting ridges form obvious diamond-shaped furrows; look for letter “A” or pattern of cantaloupe rind.

Beam #9: Eastern White Pine (Pinus strobes): Scales; dark gray to reddish-brown; thick, irregularly-shaped scales; fine horizontal lines evenly spaced along scales like lines on a legal pad.

Beam #10: Red Pine (Pinus resinosa): Scales; mottled red and grayish-brown; flaky scales; jigsaw puzzle or sandstone appearance.

Beam #11: Sugar Maple (Acer saccharum): Vertical Strips; gray to brown; finely cracked; looks like old paint; curls away from trunk on one side; look for horizontal scars indicating work of maple sugar borer.

Beam #12: Big-Tooth Aspen (Populus grandidentata): Ridges and Furrows; greenish-brown to dark gray; V-shaped furrows intersect every 6-12 inches; flattened ridges appear sanded down; gnarly look; periodic horizontal lines; on older trees resembles Northern Red Oak at bottom and Birch toward top.

Beam #13: White Oak (Quercus albra): Ridges; light gray with reddish cast; rectangular-shaped blocks with flaky surfaces; ends of blocks curl outward; feather-like in mature trees.

Beam #14: American Elm (Ulmus americana): Ridges and Furrows; ashy-gray; diamond-shaped furrows; flat-topped ridges; alternating light and dark layers like vanilla and chocolate wafer cookies.

Beam #15: Black Birch (Betula lenta): Lenticels Visible (note: all trees have lenticels, but they are more obvious on some than others. Lenticels are tiny slits in the bark that allow for gas exchange, just like our pores); gray to brown-gray to black; may crack and form scales that curl away from trunk; long, thin horizontal lenticels.

Beam #16: Paper Birch (Betula papyrifera): Peeling/Curling; white to creamy white; peeled bark reveals pink or orange tints; small, horizontal lenticels visible.

That’s it in a nutshell. Ah, but here’s the thing. Except for the American Beech, tree bark changes as a tree ages. And beech trees can be equally confusing because some are severely affected by beech scale disease. So, just when you think you know a species, you may come upon a younger or older version and get totally thrown off. The key is to take your time, walk all the way around the tree, and look at other clues like the twig and bud formation. Touch the bark. Smell it.

And take a walk across the bridge and into the park during any season. Chances are, I’ll be there doing the same.

Thanks for joining me for this lengthy wander. I hope you’ll find time to wonder about bark.