Published in Selbyana 2001.

Mark W. Moffett, Museum of Vertebrate Zoology, University of California, 3101 Valley Life Sciences, Berkeley, CA 94720, U.S.A., moffett@uclink4.berkeley.edu

Conclusions

There are species from every Kingdom of life that attach to or grow from substrates, and, when aggregated, these organisms form three-dimensionally structured communities whose parts that emerge from the substrate in aggregate can be (and often have been) described as "canopies." Terrestrial studies appear to be categorized as "canopy biology" either on the basis of inaccessibility, as when specialized gear is required to access trees (Moffett & Lowman 1995), or on the basis of the communities' coverlike properties (in the latter case, "canopy" is treated as synonymous with "overstory" or used more broadly as any stratum with sessile host organs distributed so as to appreciably shade the layers below, as the word can be used in marine science: Dayton 1975a, Baird & Hughes 2000). Because such criteria are arbitrary and of limited utility, I apply "canopy" to all above-substrate parts of sessile communities (plant communities in Moffett 2000). The common feature distinguishing studies as canopy biology is the treatment of sessile communities in three spatial dimensions, along with other attributes that may be unique to life within this "canopy space."

By projecting into a volume of fluid media, canopies can augment productivity through increasing the biotic mass and the live surface area available to capture and process nutrients and energy, and can enhance a diversity through transforming the climatic and chemical properties of the space they occupy in a heterogeneous way, potentially multiplying the niches associated with a given area of substrate (DeVries et al. 1999, Morin 2000, Moffett 2000), as well as by providing retreats from predators, competitors, or adverse conditions, and additional surface area that can to either attract or accumulate new species and the nutrients required to support a rich community (Dean & Connell 1987, Lovett & Lindberg 1992, Jones et al. 1997). A challenge for the science of comparative canopy biology is to determine the rules by which ecosystems, including both the sessile species and the residents of those species, assemble in three dimensions and thereby create opportunities for increased production and diversity.

We also must explain the differences and even more intriguing similarities in physical structure and dynamics of canopies that develop in air as contrasted with water, and across orders of magnitude in host size: for example, compare Edred Corner’s views on trees with Timothy Allen’s on microalgae (Corner 1967, Allen 1977). Surely these size extremes are of special fascination: that may be the primary reason many of us climb trees for our studies (beyond fulfilling our sense of adventure). Will scaling functions prove sufficiently linear to permit straightforward extrapolations between the extremes? Of course, our understanding of many aspects of canopy biology is in its infancy, and generalizations can be of limited value without detailed information. But even at this early stage I am confident that ideas developed for a particular type of canopy could prove useful to researchers working with other types of canopy. Ultimately, however, our knowledge of canopies must be integrated into a coherent structural ecology of sessile communities as a whole, that is by taking full account of the role of within-substrate organs such as roots and holdfasts.

ACKNOWLEDGMENTS

The core issues of canopy biology and my doubts about the commonplace restriction of discussions of canopies to forest situations were first described at a dinner lecture for the 1998 International Canopy Conference in Sarasota, Florida. Since then I have had a lot of help with these issues. For general comments I gratefully acknowledge David Benzing, Jane Hirshfield, and one anonomyous reviewer. For assistance with the philosophy of discipline formation, I thank Mary Catherine Bateson, David L. Hull, Peter Harries-Jones, George Lakoff, Paul Ryan, Blair A.M. Tindall, and Carol Wilder; for thoughts on trees, forests and the dimensionality of canopies, David Ackerly, Timothy F.H. Allen, James H. Brown, Jerome Chave, Joel Clement, Raphael Didham, Stephen P. Ellner, Thomas J. Givnish, Juan Gouda, Paul G. Jarvis, David King, Richard Law, Orie Loucks, Gary M. Lovett, Jonathan Majer, Lauri Oksanen, Karl Niklas, John M. Norman, Serguei Ponomarenko, Jonathan Silvertown, Anthony R.E. Sinclair, Steven Sutton, Bastow Wilson, Neville Winchester, and Truman Young; for information on roots, Peter W. Barlow, A. Roland Ennos, Lewis Feldman, Robert B. Jackson, Donald R. Kaplan, Krista Lõhmus, Jonathan Lynch, James H. Richards, and Yoav Waisel; for viewpoints on algal, bacterial, coral reef and other canopies, James D. Bryers, Robert C. Carpenter, J. William Costerton, Paul Dayton, Michael Dolan, Elizabeth Gladfelter, Ron Karlson, Mimi Koehl, Michael Kühl, Steven E. Lindow, Lynn Margulis, Susan Merkel, Peter J. Morin, James W. Porter, Jennifer H. Richards, Kenneth P. Sebens, Robert S. Steneck, Valerie Behan-Pelletier, Martin Wahl, Susan L. Williams, and the participants at the first-ever formal discussion between experts on marine and terrestrial canopies, organized by James Eckman and myself for the 81st annual meeting of the Western Society of Naturalists (December 2000). Lapses in coverage and logic can be attributed to me.

The figures and bibliography are not included here. Please consult the published version, given a possibility that small editorial changes may not be reflected in this text. Contact the author at naturalist@erols.com for a reprint.


Continue reading this paper:

Abstract

Seeing the Forest for the Herbs

More to Pond Scum Than Meets the Eye

The Geometry of Canopy Biology

Getting to the Root of the Matter

Conclusions

© Mark W. Moffett, please e-mail naturalist@erols.com to obtain a complete reprint.