Allelopathy in a broad spectrum of environments as illustrated by bracken

Bracken is a weed that strongly dominates a wide variety of vegetation types throughout the world. The primary mechanism of interference that this fern brings to bear upon associated plants that allows it to establish and maintain dominance is allelopathy. But due to the nature of the interaction between allelopathy and the environment, bracken has evolved a mechanism of toxin release which allows the fern to exert its dominance most effectively in each particular habitat in which it grows. In southern California, toxin release is timed for the initiation of the wet season and thus the initiation of germination of associated plants. Toxins come primarily from the dead, standing fronds. In the Pacific Northwest, toxin release is timed for the breaking of dormancy in spring after the snow melts and soil temperature rises. Toxins come primarily from bracken litter, roots and rhizomes. In tropical Costa Rica, toxin release takes place all year round, timed for the continual growth of associated plants. Toxins come primarily from a continual production by the green fronds. The interrelationship between allelopathy and the environmental complex is discussed.