Like animals, plants have gender. In almost all plants, sex is constant, but in a few species, individual plants may change their sex. This is called environmental sex determination (ESD).
New research by Jennifer Blake-Mahmud (Colgate University) and Lena Struwe (Rutgers University), just published in the American Journal of Botany, found that inflicting damage could influence the sex expression of trees. In most plants with ESD, females are generally healthier and in better condition. But in this maple species, severe damage to branches and leaves of male trees caused them to flower as females two years later. Less severe damage didn't have an effect, suggesting that some threshold exists to sex-determining cues.
Injury and tree sap (the tree's "lifeblood", so to speak) are not unrelated. In fact, injuring a tree can disrupt the flow of water and nutrients, depleting the resources in some parts of the tree, while building them up in other parts. Taken together, this research supports the idea that changes in sugar concentration in female trees might be a consequence of injury and that it is the physical damage to a tree that cues the change to female sex expression.
While some might be eager to see the tough trees turning female, it isn't so straightforward for the tree populations. Females have much higher mortality than males. With our forests experiencing increasing stressors from storms, drought, and herbivory, we might see increasing numbers of males changing sex to females. Because of the high death rate among female trees, we could expect to see higher turnover in these native striped maple populations at the expense of population stability.
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Journal
American Journal of Botany