Facilitation in plant communities: the past, the present, and the future

Abstract

1. Once neglected, the role of facilitative interactions in plant communities has received considerable attention in the last two decades, and is now widely recognized. It is timely to consider the progress made by research in this field. 2. We review the development of plant facilitation research, focusing on the history of the field, the relationship between plant–plant interactions and environmental severity gradients, and attempts to integrate facilitation into mainstream ecological theory. We then consider future directions for facilitation research. 3. With respect to our fundamental understanding of plant facilitation, clarification of the relationship between interactions and environmental gradients is central for further progress, and necessitates the design and implementation of experiments that move beyond the clear limitations of previous studies. 4. There is substantial scope for exploring indirect facilitative effects in plant communities, including their impacts on diversity and evolution, and future studies should connect the degree of non‐transitivity in plant competitive networks to community diversity and facilitative promotion of species coexistence, and explore how the role of indirect facilitation varies with environmental severity. 5. Certain ecological modelling approaches (e.g. individual‐based modelling), although thus far largely neglected, provide highly useful tools for exploring these fundamental processes. 6. Evolutionary responses might result from facilitative interactions, and consideration of facilitation might lead to re‐assessment of the evolution of plant growth forms. 7. Improved understanding of facilitation processes has direct relevance for the development of tools for ecosystem restoration, and for improving our understanding of the response of plant species and communities to environmental change drivers. 8. Attempts to apply our developing ecological knowledge would benefit from explicit recognition of the potential role of facilitative plant–plant interactions in the design and interpretation of studies from the fields of restoration and global change ecology. 9. Synthesis: Plant facilitation research provides new insights into classic ecological theory and pressing environmental issues. Awareness and understanding of facilitation should be part of the basic ecological knowledge of all plant ecologists.

This review was an outcome of the conference ‘Facilitation,Biodiversity, Invasibility in a Changing World’, held from 4 to7 September 2006 at the University of Bordeaux’s Marine Bio-logical Station, Arcachon, France. We gratefully acknowledgethe financial support provided for this meeting by theEuropean Science Foundation, and thank Pierre Chardy andXavier de Montaudouin for hosting the meeting. We thank allconference participants for stimulating discussions. R.W.B.would like to acknowledge support for writing this paperfrom the Scottish Executive Environment and Rural AffairsDepartment, and the use of Ray Callaway’s reference database for production of the supplementary material. F.T.M.acknowledges support from a Ramón y Cajal contract awardedby the Spanish Ministerio de Educación y Ciencia and fromthe British Ecological Society (ECPG 231/607).