For more than a century, ecologists have concentrated on competition as a crucial process for community organization. However, more recent experimental investigations have uncovered the striking influence of positive interactions on the organization of plant communities. Complex combinations of competition and positive interactions operating simultaneously among plant species seem to be widespread in nature. In the present paper, we reviewed the mechanism and ecological importance of positive interactions in plant communities, emphasizing the certainties and uncertainties that have made it an attractive area of research. Positive interactions, or facilitation, occur when one species enhances the survival, growth, or richness of another. The importance of facilitation in plant organization increases with abiotic stress and the relative importance of competition decreases. Only by combining plant interactions and the many fields of biology can we fully understand how and when the positive interactions occur.
(Managing editor: Ya-Qin Han)