Stepmotherly tree(tment)

Published: Thursday 31 August 2000

Artificial plantations are generally monocultures, but in general forests, many species thrive. Why this should be so is one of those questions that is so obvious that people rarely bother to ask it. Alissa Packer and Keith Clay, of Indiana University, have however, not only asked it but believe they have the answer. That answer, just published in Nature, is that parental trees are unwitting agents of destruction of their nearby offspring. They attract specialist pathogens which kill seedlings of the same species. This allows seedlings from other species, not susceptible to the pathogens to germinate without competition. Packer and Clay studied the black cherry common in Indiana and other areas of eastern North America. First they established that black cherry seedlings growing near adult trees did, indeed, do badly. They followed the fates of seedlings growing around six mature cherries and found that the average distance from the trunk of a recently germinated seed was several metres less than that of seedlings that had managed to establish themselves a few months later. If seedlings were dying at random, there should have been no difference. Being close to an adult was thus a bad thing.

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