POSITIVE INTERACTIONS AMONG PLANTS

Experimental evidence for positive interactions, or facilitation, amon g plants has increased markedly during the last 10 years. Experiments documenting facilitation have been conducted in many diverse ecologica l. systems, which suggests that positive interactions may be fundament al processes in plant communities. Here, I review the evidence for fac ilitation, the mechanisms by which facilitation operates, and the effe cts facilitation has on community structure. Facilitative mechanisms m ay act simultaneously with resource competition or allelopathy, and th e overall effect of one species on another may be the product of multi ple, complex interactions. Positive interactions may also determine co mmunity spatial patterns, permit coexistence, enhance diversity and pr oductivity, and drive community dynamics. Once viewed as anecdotal and idiosyncratic, facilitation is now contributing to a more complete un derstanding of community structure and dynamics.