The balance between positive and negative plant interactions and its relationship to environmental gradients: a model

Positive, beneficial interactions between individuals within plant communities have been observed in nature and recorded in a wide variety of ecological experiments. However, the existence of such interactions has been, and continues to be, largely ignored by most ecological researchers. We present here a new model that combines current ecological theory on plant competition, and its relationship to environmental severity, with evidence from a range of studies that show positive plant interactions in the field. The model describes a hypothetical relationship between the intensity of positive (e.g. mutualistic) and negative (e.g. competitive) interactions between members of a plant community, and the severity of the external environment, It also provides an explanation for the past and current neglect of positive plant interactions, and for the conflicting results from plant community manipulation experiments examining such phenomena. Potential directions for future research into positive plant interactions are proposed.