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

Abstract

Summary 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.

Role of invasive Melilotus officinalis in two native plant communities

“…Although we did not design our study to test the stress gradient hypothesis, in which positive interactions dominate in more stressful environments (Bertness and Callaway 1994;Brooker et al 2008;Callaway et al 2002), these results are consistent with its predictions. In the harsh sparse vegetation environment, we found a facilitative role for Melilotus, which had a consistent, positive relationship with cover of native and exotic species within a given year (Table 2).…”

Multiple cropping systems as drivers for providing multiple ecosystem services: from concepts to design

“…Species can also coexist by facilitation where one or several species provide resources or improve the environmental conditions for the other species by modifying their local biotic and/or abiotic environment, and/or the availability of limiting resources (Callaway 1995;Brooker et al 2008). For instance, the facilitation of water acquisition in drought conditions by hydraulic lift has been reported for species with different root system architectures (Caldwell et al 1998 and references therein; Pang et al 2013;Sekiya et al 2011).…”

Nucleation in tropical ecological restoration

“…Although the majority of conceptual models of community structure are either explicitly or implicitly based on competition, a large body of empirical evidence and theory has accrued supporting positive interactions, such as facilitation, as another important and general phenomenon affecting plant distributions, productivity, diversity, and reproduction (Hunter and Aarssen, 1988;DeAngelis et al, 1986;Brooker et al, 2008;Bulleri et al, 2008). Positive interactions are incredibly diverse and have a welldocumented influence on ecosystems.…”