par Billen, Gilles 
;Décamps, H.;Garnier, Josette;Boët, P.;Meybeck, M.;Servais, Pierre
Editeur scientifique Cushing, C.E.;Cummins, K.W.;Minshall, G.W.
Référence River and stream ecosystems, Elsevier, Amsterdam, Ed. 1, page (389-418)
Publication Publié, 1995
;Décamps, H.;Garnier, Josette;Boët, P.;Meybeck, M.;Servais, Pierre Editeur scientifique Cushing, C.E.;Cummins, K.W.;Minshall, G.W.
Référence River and stream ecosystems, Elsevier, Amsterdam, Ed. 1, page (389-418)
Publication Publié, 1995
Partie d'ouvrage collectif
| Résumé : | The River Continuum Concept (RCC) portrays a stream as a series of physical gradients and corresponding biological changes, and highlights the role of carbon in the dynamics of the community (Vannote et al. 1980). The concept has attracted many critics, mainly for its lack of generality, but none would deny that it has been a major stimulus for data collection and ideas in stream ecology. As a result, the peculiarities of streams have been reconciled with broader ideas in ecology and few would now argue, as did Rzoska (1979), that “rivers are not ecosystems.” Lotic ecology has also forged strong links with chemistry, geology, geomorphology, hydraulics, and hydrology. The RCC was a catalyst for these advances, and it has received some reciprocal polishing. Now in its adolescence, it remains an indicative rather than prescriptive model, but still the nearest thing we have to a paradigm or “disciplinary matrix” (cf. Kuhn 1972). This volume has the RCC as its theme and presents data for streams and rivers from 23 regions of the world. The regions are unequal, determined more by geopolitics than ecological integrity: North America is represented by 6 chapters, Europe by 7 chapters, Africa, South America, and Australia by 3, 2, and 1 chapters, respectively, and New Zealand has a chapter of its own. The first authors were free to conscript others, and the eventual 50 contributors were invited to provide a regional geographic setting plus information about community metabolism, algae, macroinvertebrates, and other elements of stream ecosystem structure and function. They were asked especially to consider the regional applicability of the RCC. In this respect the editors, Bert Cushing, Ken Cummins and Wayne Minshall, are uniquely qualified, having been contributors to the seminal RCC paper. Although the editors suggest (p. 6) that the RCC is a basis for “a general framework for conceptualizing riverine ecosystems,” even the most recent formulations of the concept do not easily accommodate the flood pulse, patch dynamics, and nutrient spiralling concepts. The literature on the role of hydraulic factors, especially by Bernhard Statzner and colleagues, may lack the packaged convenience of the other concepts, but it too contains insights that are essentially complementary to, rather than part of, the revised RCC. The RCC model is effective for many upland streams, but less applicable to big rivers (e.g. Sedell et al. 1989) where the Flood Pulse Concept may serve best (Walker et al. 1995). The editors acknowledge (p. 5) that the flood pulse is “a fundamental community organizer that over-rides longitudinal patterns along changing stream order,” but that the extent and duration of inundation “generally increase down river in a geomorphically predictable fashion . . .,” thereby reaffirming the relevance of the RCC. The consensus of the authors’ views appears to be that the RCC does provide useful insights, but that these are by no means general. The book’s geopolitical perspective will have been influenced by its place in the series Ecosystems of the World. This approach is, as Stuart Fisher says in his chapter (“Stream ecosystems of the western United States”), intellectually limiting in some respects. At one level, much of the argument over the validity and applicability of the RCC, both in this book and in the antecedent literature, has been diverted by discussion of its apparent shortcomings in regions outside the eastern U.S., where it was first developed. If concepts are seen as working models open to modification in different circumstances, talk of the RCC being “right” or “wrong” is unproductive. We may need also to recall the maxim that no model can simultaneously achieve generality, realism, and precision (Levins 1968). At another level, Fisher suggests that comparisons between streams of similar character in remote parts of the world would be useful. For example, global comparisons between dryland streams could be insightful. It follows that the strengths of the RCC probably are The River Continuum Concept (RCC) portrays a stream as a series of physical gradients and corresponding biological changes, and highlights the role of carbon in the dynamics of the community (Vannote et al. 1980). The concept has attracted many critics, mainly for its lack of generality, but none would deny that it has been a major stimulus for data collection and ideas in stream ecology. As a result, the peculiarities of streams have been reconciled with broader ideas in ecology and few would now argue, as did Rzoska (1979), that “rivers are not ecosystems.” Lotic ecology has also forged strong links with chemistry, geology, geomorphology, hydraulics, and hydrology. The RCC was a catalyst for these advances, and it has received some reciprocal polishing. Now in its adolescence, it remains an indicative rather than prescriptive model, but still the nearest thing we have to a paradigm or “disciplinary matrix” (cf. Kuhn 1972). This volume has the RCC as its theme and presents data for streams and rivers from 23 regions of the world. The regions are unequal, determined more by geopolitics than ecological integrity: North America is represented by 6 chapters, Europe by 7 chapters, Africa, South America, and Australia by 3, 2, and 1 chapters, respectively, and New Zealand has a chapter of its own. The first authors were free to conscript others, and the eventual 50 contributors were invited to provide a regional geographic setting plus information about community metabolism, algae, macroinvertebrates, and other elements of stream ecosystem structure and function. They were asked especially to consider the regional applicability of the RCC. In this respect the editors, Bert Cushing, Ken Cummins and Wayne Minshall, are uniquely qualified, having been contributors to the seminal RCC paper. Although the editors suggest (p. 6) that the RCC is a basis for “a general framework for conceptualizing riverine ecosystems,” even the most recent formulations of the concept do not easily accommodate the flood pulse, patch dynamics, and nutrient spiralling concepts. The literature on the role of hydraulic factors, especially by Bernhard Statzner and colleagues, may lack the packaged convenience of the other concepts, but it too contains insights that are essentially complementary to, rather than part of, the revised RCC. The RCC model is effective for many upland streams, but less applicable to big rivers (e.g. Sedell et al. 1989) where the Flood Pulse Concept may serve best (Walker et al. 1995). The editors acknowledge (p. 5) that the flood pulse is “a fundamental community organizer that over-rides longitudinal patterns along changing stream order,” but that the extent and duration of inundation “generally increase down river in a geomorphically predictable fashion . . .,” thereby reaffirming the relevance of the RCC. The consensus of the authors’ views appears to be that the RCC does provide useful insights, but that these are by no means general. The book’s geopolitical perspective will have been influenced by its place in the series Ecosystems of the World. This approach is, as Stuart Fisher says in his chapter (“Stream ecosystems of the western United States”), intellectually limiting in some respects. At one level, much of the argument over the validity and applicability of the RCC, both in this book and in the antecedent literature, has been diverted by discussion of its apparent shortcomings in regions outside the eastern U.S., where it was first developed. If concepts are seen as working models open to modification in different circumstances, talk of the RCC being “right” or “wrong” is unproductive. We may need also to recall the maxim that no model can simultaneously achieve generality, realism, and precision (Levins 1968). At another level, Fisher suggests that comparisons between streams of similar character in remote parts of the world would be useful. For example, global comparisons between dryland streams could be insightful. It follows that the strengths of the RCC probably are best revealed in comparisons between streams in environments like those of the Eastern Deciduous Forest Biome. The book, however, is not a conceptual synthesis; that remains a challenge, perhaps for contributors to a future symposium. A new synthesis would provide opportunities for extension and clarification. Several authors, including Rosemary MacKay (“River and stream ecosystems of Canada”) and Bemhard Statzner and Fritz Kohmann (“River and stream ecosystems in Austria, Germany and Switzerland”), are critical of our preoccupation with natural streams rather than disturbed rivers. Were it not for the corollary Serial Discontinuity Concept, recently given a lowland, floodplain perspective (Ward and Stan ford 1995) the RCC and related concepts would say little of the impacts of humans on lotic ecosystems. A synthesis might also settle confusion over matters of scale (e.g. “rivers” vs. “streams”), the reality of “functional feeding groups,” the boundary between particulate and dissolved organic matter, the rationale for separating macroinvertebrates from other organisms, and other shadowy terms in the stream ecology lexicon. The editors have not attempted a geographic synthesis other than that contained in the chapters themselves. Some authors had extensive data to draw upon and provide valuable summaries of the supporting literature. Others had less information to work with; their accounts are necessarily more descriptive but often thoughtful and very readable [e.g. see those of David Dudgeon (“The ecology of rivers and streams in tropical Asia”) and A. D. Harrison (“Northeastern Africa rivers and streams”)]. The chapter by J. R. Webster et al. (“Organic processes in streams of the eastern United States”) is a natural attraction among the many. The authors had access to a formidable body of data and venture a statistical analysis seeking relationships between stream size and carbon pathways. This is only partly successful, as the data are for relatively few sites and derived from a wide variety of methods, and rivers are little represented. It is assumed that the conventional statistical criterion for significance (P = 0.05) has real ecological significance. Readers may founder in statements like “. . . the scraper data did display a weak fit to a thirdorder polynomial regression (r 2 = 0.33), suggesting a tendency for greater proportional scraper production in mid-sized streams” (p. 171). Even in the RCC’s heartland, then, evaluations are limited by the availability of numerical data. Faced with wide variability, in tropical as well as temperate streams, many authors persist in citing measurements without reference to reliability or reproducibility. Derek Westlake and Mike Ladle (“River and stream ecosystems of Great Britain”) suggest that, if streams and rivers are to be seen as intact ecosystems, the need for data may never be satisfied. The immediacy of problems in conservation and management means that we may need to limit our “stamp-collecting” and gather albums instead! If this book does not quite succeed as a conceptual or geographic synthesis, it certainly does so as a compilation of diverse data. It is a point of entry to the global lotic literature, including areas where neither the literature or the streams and rivers are easily accessible. As with most academic volumes its cost might discourage individual purchasers, but it is indeed a valuable resource for an institutional library. |
