Gestion basée sur les écosystèmes côtiers avec des fonctions et des valeurs écologiques non linéaires

Numéro d'étude :

51

Auteur:

E. B. Barbier, E. W. Koch, B. R. Silliman, S. D. Hacker, E. Wolanski, J. Primavera, E. F. Granek, S. Polasky, S. Aswani, L. A. Cramer, D. M. Stoms, C. J. Kennedy, D. Bael, C. V. Kappel, G. M. E. Perillo, and D. J. Reed.

Abstrait:

A common assumption is that ecosystem services respond linearly to changes in habitat size. This assumption leads frequently to an "all or none» choice of either preserving coastal habitats or converting them to human use. However, our survey of wave attenuation data from field studies of mangroves, salt marshes, seagrass beds, near shore coral reefs, and sand dunes reveals that these relationships are rarely linear. By incorporating nonlinear wave attenuation in estimating coastal protection values of mangroves in Thailand, we show that the optimal land use option may instead be the integration of development and conservation consistent with ecosystem-based management goals. This result suggests that reconciling competing demands on coastal habitats should not always result in stark preservation-versus-conversion choices.

Principaux résultats et conclusions :

• Ecosystem-based management (EBS) is discussed as a technique to justify the maintenance of natural ecosystems by valuing their ecosystem services (321).
• This study showed, among other things, that the relationship between mangrove habitat and the ecosystem services that they provide are non-linear: “These field data reveal that for all these coastal habitats, nonlinear relationships exist between habitat area and measurements of the ecosystem function of wave attenuation (fig. S1). For mangroves and salt marshes, there are quadratic and exponential decreases, respectively, in wave height with increasing habitat distance inland from the shoreline (fig. S1, A and B)…These data suggest that the assumption of linearity is likely to be inaccurate for many ecosystem services that depend on habitat size—a result that could have important implications for conservation, especially as it relates to EBM”(322).
• Based on this study’s results, the following data show that complete mangrove conservation outweighs the benefits of conversion of mangrove habitat to shrimp farms: “The aggregate value of the mangrove system is at its highest ($18.98 million) when it is completely preserved, and any conversion to shrimp farming would lead to less aggregate value compared to full preservation. Thus, an EBM strategy that considers all the values of the ecosystem would favor mangrove preservation and no shrimp farm conversion”(322).
• It is possible for mangrove habitat conservation to come to a happy medium between complete conservation and complete la déforestation: “Using the nonlinear wave attenuation function for mangroves…The storm protection service of mangroves still dominates all values, but small losses in mangroves will not cause the economic benefits of storm buffering by mangroves to fall precipitously (Fig. 2A). The consequence is that the aggregate value across all uses of the mangroves (i.e., shrimp farming and ecosystem values) is at its highest ($17.5 million) when up to 2 km2 of mangroves are allowed to be converted to shrimp pisciculture and the remainder of the ecosystem is preserved…Local mangrove-dependent coastal communities and other coastal communities living within 5 km inland would obtain approximately the same share of economic benefits from the mangrove system ($15.6 and $13.2 million, respectively), but now outside investors would earn some commercial profits from shrimp farming ($1.9 million). Finally, we note that the outcome from our Thailand mangrove valuation example corresponds to "best practice» guidelines for mangrove management in Asia, which recommend that ideal mangrove/pond ratios should not exceed 20% of the habitat area converted to ponds (Saenger et al 1983; Primavera et al 2007)”(322-323).

Ouvrages cités:

J. H. Primavera, J. P. Altamirano, M. J. H. L. Lebata, A. A. delos Reyes Jr., and C. L. Pitogo. 2007. Mangroves and Shrimp Pond Culture Effluents in Aklan, Panay Island, Central Philippines. Bulletin of Marine Science 80(3): 795-804.

Saenger, P., E. Hegerl, and J. Davie. 1983. Global Status of Mangrove Ecosystems. IUCN, Gland, Switzerland.