by Bob Thomas
Most of us rarely consider that plants have to compete among themselves for space, sunshine, nutrients, and other vital resources. Some methods that may come to mind are different growth rates and variation in leaf arrangement, shape of crown, and overall height.
One way that may be surprising is termed allelopathy, or a plant’s production of its own herbicides. These phytotoxins, or “plant killers,” inhibit the growth of other types of plants. Their production is more common in desert regions since rainfall often washes them from the soil and provides a good substrate for microbial degradation. There are, however, a number of plants in the New Orleans area that use allelopathy.
The oaks and magnolias are good examples. The produce tannins that ward off encroaching competitors. Many of us have tried in vain to grow grass in their shade. We have raked, planted, fertilized, added soil, and prayed, but with rare success. Since all of a tree’s resources must come from the area reached by its roots, typically under its foliage, it should not be surprising that they have developed a means to keep other plants out of their “pantry.”
Another example is golden rod, a beautiful bright yellow fall flower that grows in open, sunny places. The phytotoxin produced by these plants inhibits the growth of woody plants such as trees. When you think about it, it makes sense that a plant requiring an abundance of sunlight would have a method to prevent itself from being shaded out by taller, more permanent plants.
These phytotoxins have received little public attention to date, but in the future humans will surely make more use of Mother Nature’s safe herbicides.
Also published in Nature Profile, The Times Picayune, April 21, 1982.