Indirect facilitation as a structuring mechanism of submersed aquatic plants : a buffering role under biotic and abiotic constraints

Direct facilitation among plants has recently been included into the humped-back diversitybiomass relationship along environmental severity gradients. However, recent evidence stresses the occurrence of indirect facilitation due to biotic disturbance under a wide range of environmental severity, and including indirect facilitation will thus bring these conceptual frameworks up to date. We propose a new conceptual model of variation in plant interactions along both biotic disturbance and environmental severity gradients, combining earlier models and theories into an integrated approach. This response surface model underlines a peak of direct/indirect facilitation related to hot-spots of diversity in intermediately severe and biotically disturbed environments, and explains how plant communities might expand into, or be excluded from, harsh and biotically disturbed environments.