“Mommy, Daddy, where do trees come from?” Whew! At last, a simple question.
The Clones are Already Here!
By Bruce Rottink, Volunteer Nature Guide and retired Research Forester
“Mommy, Daddy, where do trees come from?”
Whew! At last, a simple question. Since all trees are what scientists call “seed plants”, the obvious answer is – a seed. Well, that’s mostly true, but there are some interesting twists and turns along the way.
Trees in Tryon Creek State Natural Area produce unfathomably large amounts of seed. Last September a bigleaf maple (Acer macrophyllum) tree at Tryon Creek crashed to the ground during a rain storm. From this tree, I sampled the single branch shown in the photo below.
Considering the entire Tryon Creek forest, this one branch is insignificant. And yet, when I stripped off all the seeds that it had produced that year, there were 1,024 seeds on this single branch. As you can see in the photo below, that’s more than 1-1/2 quarts of maple seeds! More than enough seeds to completely reforest an entire acre, a square of land more than 200 feet by 200 feet in size.
1,024 big leaf maple seeds!
In spite of this prolific seed production, there are many maples at Tryon Creek which did not start directly from a seed!
Maple trees have a tendency to produce small branches, called sprouts, near the base of the tree trunk. One example is shown in the photo below.
When a mature maple is cut down, or if the top breaks off in a storm, this basal sprouting kicks into high gear!
Occasionally in the forest, you will see a tight cluster of maple trees growing from a single spot. You might suspect that several seeds landed close together, germinated and formed this cluster of trees. For example, with this pair of maples below.
However, at least sometimes it is obvious that the trees are all clustered around the remnants of a long dead tree. In the case of these “twin” maples, the remnants of the old parent tree, as seen in the picture below, are reduced to a mere stub of dead wood sticking up in the crotch between the two stems.
Thus what might appear to be multiple maple trees are really just multiple mature sprouts from one “parent” tree. The sprouts grow quickly using both the food stored in the parent tree roots, and the established network of roots.
This sprouting habit helps the forest recover quickly from disturbance.
Black Cottonwood Clones!
Another tree which sometimes reproduces itself without using seed is Tryon Creek’s black cottonwood (Populus balsamifera ssp.trichocarpa). Black cottonwood clones itself in a very dramatic fashion. If a branch breaks off a tree, and falls onto moist ground, a new tree can start from that branch. Jennifer Primm, Tryon Creek’s newest Ranger, and I found the example in the photo below while hiking on Old Main Trail this spring.
Note that it has all the essentials for a young tree – buds, branches and, of course, several white roots. This youngster had the buds and stems when it broke off the parent tree. The roots, however, developed after it fell to the moist ground.
Once it hit the ground, at the point where the branch broke off, cells within the stem started to grow, divide and expand. Had the branch remained on the tree, these cells would have produced wood and bark for the twig. However, under these new circumstances they developed into a blob of poorly organized (scientists say “undifferentiated”) cells called a callus. We can see the callus in the photo below. The surface of a callus tends to be a bit lumpy and irregular. What you see here is not just dirt stuck to the end of the stem. It is plant tissue. If this callus had been developed in a laboratory, it would be pure white, but here the callus has probably been stained brown by the soil.
After the callus forms, some of the cells within the callus start to differentiate and get organized. Depending upon the environment of the callus, and it’s location on the plant, these cells might become roots, leaves or some other plant part. Here, growing at the base of a twig, the callus typically develops roots. This new plant, of course, will be genetically identical to the parent tree, in other words, a clone of the parent.
This ability of cottonwoods to root from a piece of stem has important commercial applications. Many years ago I worked as a Research Forester. Then I was involved in developing and testing techniques for establishing cottonwood plantations. The company I worked for set up some of the first cottonwood plantations in the lower Columbia River bottomlands, and irrigated plantations near Boardman, in eastern Oregon. All of the trees in these plantations were established using “cuttings” which were 1 foot long pieces of cottonwood branches anywhere from ½ to 1 full inch in diameter. The cuttings were taken in the winter, and planted in early spring. Nearly all the cuttings rooted and created new trees. The success of these early test plantations resulted in the extensive commercial cottonwood plantations that you see today in those two areas.
So while vegetatively produced trees are the exception, they provide an interesting aspect of tree life at Tryon Creek. While all the trees at Tryon Creek SNA may have originally come from a seed, a few of them have some odd twists in their family tree (I couldn’t resist!) The next time you’re at Tryon Creek, see how many maple trunks growing in a clump you can find.