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Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Variation in the Flora and Fauna of Tidal Freshwater Forest Ecosystems Along the Columbia River Estuary Gradient: Controlling Factors in the Context of River Flow Regulation
Auteurs :	Laura Kathleen Johnson, Auteur ; Charles A. Simenstad, Auteur
Type de document :	Article
Dans :	Estuaries and Coasts (38(2) MAR 2015)
Article en page(s) :	679-698
Résumé :	Tidal freshwater forested wetlands are dynamic, complex ecosystems that typically occur in large, floodplain river estuaries throughout the world. The estuarine portion of the Columbia River, in the Pacific Northwest region of North America, is exceptionally large and extends from the Pacific Ocean to the head of tide at Bonneville Dam, located at river kilometer (RKm) 233. Our study focused on the freshwater portion of the estuarine gradient (RKm 40 to RKm 233) of the Columbia River estuary and the corresponding continuum of hydrologic regimes and biotic communities. Several diverse forested wetland community types occurred along this freshwater estuarine gradient with major shifts in community composition corresponding to the transition from predominantly tidal to predominantly fluvial hydrologic regimes. We quantitatively characterized the floristic structure, species composition, and species richness of these tidal wetlands. Additionally, we documented variation in the avifaunal and insect assemblages associated with the floral structure. We found that freshwater tidal forested wetlands in the lower reaches of the estuary were characterized by high vegetation species richness and complex forest and scrub-shrub ecosystems, while tidal wetlands in the upper reaches of the estuary displayed a greater diversity of wetland ecosystems (forested, scrub-shrub, emergent, and aquatic bed) but comparatively lower species richness. A transitional area in the mid-estuary contained forested wetlands that exhibited some similarities to estuarine forested wetlands in both the upper and lower reaches. Likewise, avifauna and insect assemblage composition transitioned along the tidal freshwater estuarine gradient. Differences in geomorphological and hydrological regimes along the estuarine gradient appear to be the factors controlling the variation in tidal freshwater forested wetland characteristics and species composition. A thorough understanding of this complex and understudied system is necessary for predicting the potential impacts of hydrologic regime alterations and climate change and for guiding ongoing restoration efforts in the region.

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