By Lawrence J. Winship
Editor’s note: This post accompanies the Earth Matters column for August 12.
What made the pine trees take such an odd, curvy shape? In short, snow and ice! But there is much more to the story. Several factors came into play, in the correct sequence, to shape the trees, and perhaps that is why their appearance is so startling and rare.
As a young plant biology and ecology teacher at Hampshire College in the early 1980s, I took frequent walks into the surrounding woods looking for useful spots for field trips and studies. The College is built on land made up of several old New England farms, with a varied and particular history of land use and abandonment, setting up numerous “natural” ecology experiments. On one such walk I came upon a patch of white pine saplings that was very dense. Hundreds, even thousands of stems occupied a more or less rectangular piece of ground along an old woods road, on a sandy rise, surrounded by re-growing hardwood and pine woods. After a little asking around I found out that it had been a horse pasture 10 years or so before, consistent with the presence of older tall red cedars amongst the pines. Horses and cows don’t eat down seedlings of eastern red cedar, so they are present on most old pasture sites. Thus, step one in the bendy tree mystery is the presence of a very dense patch of very thin (less than one inch in diameter) and tall (8 feet) white pine saplings, the result of pasture abandonment following years of grazing, on a sandy site surrounded by very large mature pines as a seed source.
While this stand of pines was not unique — white pine seedlings often mass colonize abandoned pastures on sandy soils in New England — this patch was nearby and a perfect teaching setup. The trees were a result of a known land use history, and because one can determine the age of a pine sapling, more or less, by counting the number of whorls of branches (only one per year), students could determine the year of establishment easily without cutting down any trees. And, the trees showed a dramatic height, and hence growth-rate, pattern — high in the center of the stand (tall saplings) and low at the edge (very short) with the same number of whorls. Here was a great example of resource limitation (light) and the effect on biomass accumulation. Moreover, the trees were beginning to show a classic thinning response, with any somewhat shorter trees in the middle of the patch beginning to die as the more rapid growing, or fortunate, saplings around them “won” the fight for light. I really liked this patch of trees!
Imagine my dismay when one late autumn day, scouting for a field trip after a particularly rapid, heavy and windy ice storm, I went out to my favorite patch of pine saplings and found many of them flat as a pancake. Nearby birches and maples were arched over, with their tips on or touching the ground. Deciduous trees of all sizes still had leaves on and so were really loaded with ice and snow. Branches and stems were breaking even as I watched. The pines were not arched over, but rather were bent sharply at the base. I figured there was no way they would recover, and I had lost a perfectly wonderful field site to the ravages of New England weather. I should have known better. So, step two was an early season ice storm.
Several years later a particularly energetic and creative forest ecology student decided to concentrate on his art, rather than science. Hiding my disappointment (actually, he is a tremendously gifted artist — I was glad for him, and just a little sad for myself to have “lost” a potential collaborator!) I asked to see his recent efforts. Surprised once again (this happens often at Hampshire) I followed as he led me out towards my neglected pine tree site. There, hanging in mid-air from vines strung amid huge pines, was an enormous circle (20 feet across) made up of dozens of perfectly curved pine tree trunks, each tapering from about 5 inches to a slender top. He had taken some of the dramatically curved, dying suppressed stems from the nearby old horse pasture to build his sculpture — amazing. But more amazing still was the fact that the saplings in “my” pine stand were not dead — they had rebounded and continued to grow! So step three was the fact that because the saplings were so slender, and perhaps pliable late in the Fall, they did not break and the intact xylem still carried water up from the roots, and the intact phloem still carried sugars and nutrients to the growing cambium — the trees not only survived they grew rapidly.
The shape of the existing, thriving trees tells the story. The sharp bend at the base of these trees came from the initial crush of ice and snow. Other bent trees, such as can be seen frequently on steep slopes, form as the tree tips over in response to slow downhill soil creep. The older trunk becomes less vertical and the growing tip responds to gravity, re-establishing vertical growth year after year. But there is no sharp bend at the base. And, our bendy trees are growing on a very flat site.
The long upward sweep of our bendy trees was caused by reaction wood. The trees began to put on wood eccentrically. We sacrificed one tree and dissected the stem to observe the full shape and pattern of the growth rings. The rings are perfectly round before the ice storm. Immediately afterwards they became ellipses, with the long axis of the ellipse in the plane of the re-curving stem. One of the foci of the ellipse coincides with the pith at the center of original stem. The trees were actually able to push their bent stems back up into the air, partly with the stored forces of compression and tension in the stem caused by the ice, and then the formation of brightly colored reaction wood. Finally, the very tips of these trees once again grew straight up into the air, and that bend marks the time when the recurved bending of the stem stopped.
I know of only one other documented site with bent pines like ours. They claim there is still a mystery about the trees in Poland. I bet it was an ice storm, just like ours — the secret’s in the wood!
Lawrence J. Winship, a former member of the Hitchcock Center board, is a professor of botany in the School of Natural Science.
Earth Matters, written by staff and associates of the Hitchcock Center for the Environment at 525 South Pleasant St., Amherst, appears every other week in the Daily Hampshire Gazette. For more information, call 413-256-6006, or write to us.Click here to return to full list of Earth Matters articles.