Landscape Confidential: Forked trees – VTDigger

May 13, 2013 by  
Filed under Wind Energy Tips

The lateral shoots take over as the primary trunks after a white pine's growing tip has been damaged by the white pine weevil. The result looks like a two-tined pitchfork. Photo by Audrey Clark

The lateral shoots take over as the primary trunks after a white pine’s growing tip has been damaged by the white pine weevil. The result looks like a two-tined pitchfork. Photo by Audrey Clark

 

Editor’s note: Landscape Confidential is an occasional column by Audrey Clark, a curatorial assistant at the Pringle Herbarium at the University of Vermont.

It’s a hulking, dark tree. Its trunk is more than 3 feet in diameter and black, jagged branches jut from its entire length. Fifteen feet up, the trunk splits neatly in two. The thick trunks curve outward slightly like a two-tined pitchfork and then continue upward toward the feathery evergreen canopy. Around this tree is a forest, the trees perhaps as tall but not nearly as thick. The fork in the trunk well above any animal’s browsing height is a dead giveaway to what kind of environment this tree grew up in.

Not far from the pitchfork tree is a cluster of smooth, gray-trunked trees. Their trunks splay outward in a perfect circle. When you wrap a hand around one of these trees, your fingers nearly meet. If you climb inside this wooden cell — pause for a moment to grasp two of the trunks and cry “Hey! Let me out!” — and then bend down and clear the leaves away at the center of the trees, you’ll find the floor of your cell is smooth wood, hewn flat.

A few minutes hike from these two trees is a shady glade, where you find a tree forked in the opposite direction: the reddish trunk is straight and smooth, but the roots split aboveground as if the tree is walking around on several legs.

These trees each encountered a force in their lives that shaped them in recognizable patterns. If you know what these patterns mean, you know a little bit about the history of the woods around you.

The first tree is called a wolf tree, a white pine that once stood alone in a field. In the open sun, its lower branches got just about as much sun as its higher branches, and so they survived, growing thick along the trunk. The tree grew straight and fast in the sun, but when it reached a height of 15 feet, it was discovered by a female white pine weevil who had business to take care of.

Weevils, beetles with Gonzo-like noses, are hands-down one of the cutest insects. Many of them are also nuisances. White pine weevils are nuisances to white pines and to foresters. The female beetles lay their eggs in the growing tips of white pines. They want their larvae to be warm and healthy, so the females choose pines that are out in the sun and still growing fast. When the larvae hatch, they eat the tip of the pine, where the tree has concentrated nutrients for growth.

Laura Hill Bermingham is a lecturer and research associate at the University of Vermont. She says that the funny forked look of many wolf trees is due to a mechanism that helps trees grow toward their main energy source.

A red maple, about two feet in diameter, was cut down and the stump resprouted, producing a ring of trees. Lens cap in center shows scale. Photo by Audrey Clark

A red maple, about two feet in diameter, was cut down and the stump resprouted, producing a ring of trees. Lens cap in center shows scale. Photo by Audrey Clark

“Plants want to grow up and up toward the sun,” Bermingham said. “This is controlled by a hormone called auxin, which suppresses the growth of the side shoots. When you remove the terminal bud, where auxin is produced, it stimulates the lateral shoots. So those become the top buds at that point.”

Take away the source of auxin and the two side buds on a pine take over dominance as the primary growing tips.

But why would a white pine be growing in an open field, anyway? Because the field was cleared by humans. A wolf tree is a clear sign that the land around it was once farmed or grazed. Indeed, most of Vermont’s forests were cleared in the late 1800s, which is why wolf trees can be found all over the state.

The second tree — and yes, the cluster is one tree — is another clear sign of human presence in the not too distant past. That smooth, wooden floor in your miniature prison is an old tree stump. The circle of trees are grown-up stump sprouts. At some point, someone chopped down a tree and the tree responded by sprouting from the stump, a growth pattern called coppicing. In fact, you often find whole stands of coppiced trees. In Europe, it is a forestry practice that allows for quick regrowth after cutting.

The third tree, the walking tree, tells the story of a natural influence. This tree is a hemlock, but it could just as well be a yellow birch — both trees have small seeds that tolerate growing up in shady forests. Once, before this tree was born, there was a strong wind that blew down a tree.

A nurse log doesn't have to be a log.  This yellow birch landed as a seed on a mossy stump, the rotted remains of which are still visible between the birch's ''legs.'' Photo by Audrey Clark

A nurse log doesn’t have to be a log. This yellow birch landed as a seed on a mossy stump, the rotted remains of which are still visible between the birch’s ”legs.” Photo by Audrey Clark

Over decades, dirt collected in the furrows in the fallen tree and moss grew along its length. The moss and dirt provided nutrients and held moisture, and when a seed landed there, it was a lovely place to germinate. The seed grew into a seedling, spreading its roots across and around the rotting log. At the same time, the log rotted away, leaving a tree that looks like it is straddling air. In fact, you might find a few of these hemlocks lined up in a row, straddling a long-gone log.

Bermingham says auxin, the hormone that tells a tree’s buds to grow upward, also tells its roots to grow downward. “Auxin has the opposite effect in roots as it does in the shoots. In the shoots, it senses light, and it’s growing toward the light. In the roots, it senses gravity and grows down.”

(Bermingham is quick to point out that the exact mechanisms of tree growth are complicated and controlled by more than one hormone, but auxin is a well-studied hormone that controls a good deal of plant growth.)

Taken together, these three kinds of trees tell a story about their forest. The forked pine reveals that this land was cleared for farming or pasture, probably in the late 1800s. After the land was abandoned, a forest grew back. The coppiced maple chronicles that second forest, which was at least partly logged. Because the stump is still visible at the base of the tree cluster, and because the resprouts are still small enough to wrap a hand around, it’s likely the hewing took place in the last few decades. The shady hemlock grove where the walking trees stride is probably a part of that second-growth forest. Sometime in the last hundred years a windstorm — quite possibly the storm of 1938 — knocked down trees, laying the foundation for a strangely forked row of hemlocks.

If you want to know more about these kinds of trees as well as other ways to understand patterns in the land, read Tom Wessels’ utterly classic “Reading the Forested Landscape: A Natural History of New England” (1997, The Countryman Press).

Comments are closed.