Allelopathy

I'm sure most of you have noticed the strong odors given off by plants such as sagebrush, black sage and California Bay Laurel. One of the reasons for these odors is to discourage browsing by big and little animals. Another reason, however, is to suppress the growth of a nearby plant. These toxins, called allelochemicals, permeate the soil around a plant and act as germination inhibitors. Because these allelochermicals are present, seeds from a nearby plant, although spread over a large area, can remain dormant for decades. Since the toxins are hydrocarbons, they are burned when a fire roars through the area. Once the toxins are destroyed, the seeds can flourish and this is what gives a fire scar bounteous flowers that haven't been seen in years. We have several such flower seeds in our Open Space and one of them is called the Flame Poppy or Fire Poppy (Papaver californicum) that actually requires fire to effectively germinate.

One of the best places to look for the effectiveness of allelopathic plants is in the desert where you see virtually no vegetation growing near many species of desert plants. That's what makes walking in the desert so enjoyable: these wide-open pathways between plants.

Jerry Fritzke
June 2003