The Editor’s Choice for this issue of Journal of Ecology, the paper ‘Early successional woody plants facilitate and ferns inhibit forest development on Puerto Rican landslides’ by Lawrence Walker, Frederick Landau, Eduardo Velázquez, Aaron Shiels and Ashley Sparrow, is an excellent illustration of how to blend the classic ecological issue of succession with the contemporary concepts of facilitation and competition.
Seeking to understand successional patterns has been at the forefront of ecological field studies since Cowles’ ground breaking work on the Lake Michigan dunes in the late 19th century (Cowles 1899). While general patterns of plant succession are well documented, our understanding of underlying mechanisms is still limited and this has generated one of the most well-known and controversial disputes in the ecological literature: the organismic view of Clements (1936) versus the individualistic hypothesis of Gleason (1926). Even Sir Arthur Tansley, the former British Ecological Society President and Journal of Ecology founder, weighed in on this issue, describing succession by way of an analogy of fighting barbarian invaders and the development of civilization (Tansley 1920).
The balance between facilitation and competition in communities is not new (Connell & Slatyer 1977), but it is currently a ‘hot topic’ in ecology (Maestre et al. 2009, and Bowker et al. in this issue). Indeed, Journal of Ecology has recently been leading the way in publishing key papers on plant facilitation (e.g. the Special Feature ‘Facilitation in Plant Communities’, guest-edited by Brooker & Callaway (2009). Modern views on facilitation have subsequently led to a resurgence of interest in seeking a mechanistic understanding of the concept succession (Verdú et al. 2009).
Walker and colleagues’ study is of particular importance in this debate because the authors utilized a long-term (7-year) experimental approach to studying a topic that is so often interpreted on the basis of observational patterns. In a carefully designed study, they removed early successional species of three functional groups (woody plants, scrambling ferns and tree ferns) from landslides in the tropical forests of the Luquillo Experimental Forest, Puerto Rico. Effects of the removals on vegetation succession depended on which functional groups were removed or retained on the landslides. Early successional woody plants and tree ferns appeared in combination to be facilitating long-term forest development as richness of late-successional woody plants decreased when they were removed. By contrast, scrambling ferns, which occurred in dense stands on the landslides, inhibited succession by decreasing forb and woody plant richness compared with removal plots. Tree ferns also inhibited forest development by decreasing woody plant richness and cover. Removal of these functional groups altered the prevailing abiotic factors; light availability increased when scrambling ferns were removed, and the light availability and soil pH changed when tree ferns were removed.
Overall, the results of this experimental study illustrate the contrasting effects of competition and facilitation on early succession in tropical forests. However, the story is not as clear cut as this because differences among landslides and the effects of stochastic processes, such as species arrival order, life-form of colonizing species and the competitive interactions among colonizing species, make projecting successional trajectories difficult. The authors conclude that their study shows that rain forest succession is directed by the contrasting facilitative role of early successional woody plants and the inhibitive role of scrambling ferns and tree ferns. Other studies have suggested that facilitative dynamics in early succession are driven by phylogenetically distant lineages (Verdú et al. 2009). However, this study suggests that early successional species may nevertheless have certain life- history features in common. Barbarian invaders aside, there is much still to be learned about succession that experimental work and the incorporation of modern ideas can inform us about.
Editor, Journal of Ecology
- Bowker, M., F. Maestre, & Soliveres, S. (2010) Competition increases with abiotic stress and regulates the diversity of biological soil crusts. Journal of Ecology, 98, 551-560.
- Brooker, R.W. & Callaway, R.M. (2009) Editorial: Facilitation in the conceptual melting pot. Journal of Ecology, 97, 1117-1120.
- Clements, F.E. (1936) Nature and structure of the climax. Journal of Ecology, 24, 252-284
- Connell, J.H. & Slatyer, R.O. (1977) Mechanisms of succession in natural communities and their role in community stability and organization. The American Naturalist, 163, 823-843.
- Cowles, H.C. (1899) The ecological relations of the vegetation of the sand dunes of Lake Michigan. Botanical Gazette, 27, 95-117, 167-202, 281-308, 361-91.
- Gleason, H.A (1926) The individualistic concept of the plant succession. Bulletin of the Torrey Botanical Club, 53, 7-26,
- Maestre, F.T., R.M. Callaway, F. Valladares, & Lortie, C.J. (2009) Refining the stress-gradient hypothesis for competition and facilitation in plant communities. Journal of Ecology, 97, 199-205.
- Tansley, A.G. (1920) The classification of vegetation and the concept of development. Journal of Ecology, 8, 118-149.
- Verdú, M., P.J. Rey, J.M. Alcántara, G. Siles, & Valiente-Banuet, A. (2009) Phylogenetic signatures of facilitation and competition in successional communities. Journal of Ecology, 97, 1171-1181.
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