The Ecological Biogeography of an Oregon Coastal Salt Marsh

The Ecological Biogeography of an Oregon Coastal Salt Marsh H. Peter Eilers* AcoMMON feature of coastal biogeography is an observable sequence of plant species and plant communities within the limits of tidal inundation.1 In order to learn the extent of this zonation in Oregon coastal salt marshes and the ways in which plants and plant communities are distributed with respect to elevation and duration of tidal inundation, I have investigated a portion of the Nehalem Bay salt marsh that has remained virtually undisturbed by man. Coastal salt marshes occur in environments of periodic stress because of tidal inundation and are thus the habitat for hardy halophytic or salt-tolerant plant species. Physiognomically, salt marshes resemble a graminaceous meadow in which is embedded a tortuous, dendritic system of creek channels functioning as a distributary and drainage network. The emergent nature of the Oregon coast and the high-wave energy present prevent salt marsh development in all but sheltered estuaries of major rivers, shallow water bays, and along the inland side of coastal dunes. Oregon coastal salt marshes were first surveyed in the late 1800's by the United States Coast and Geodetic Survey.2 The earliest * Dr. Eilers is Assistant Professor of Geography at California State University , Fullerton 92634. This paper was presented at the 1974 meeting of the Association at Corvallis, Oregon. 1 V. J. Chapman, Coastal Vegetation (New York: Pergamon Press, 19T4), pp. 1-2. See also M. S. Doty, "Critical Tide Factors That Are Correlated with Vertical Distribution of Marine Algae and Other Organisms along the Pacific Coast," Ecology (early spring, 1946), p. 315. 2 See for example, U.S. Army Corps of Engineers, "Survey of the Mouth of the Nehalem River," Report of the Chief of Engineers (Washington, D.C.: Government Printing Office, 1875), pp. 639-641. 19 20ASSOCIATION OF PACIFIC COAST GEOGRAPHERS biogeographic work, however, is that of House, who included a description of the Coos Bay marshes in his general treatment of the vegetation of the Coos Bay region.3 More recently, Johannessen has investigated the recent history of physical changes in several Oregon salt marshes including the marshes of Nehalem Bay.4 Other investigations of Oregon coastal marshes have dealt with insect and mollusc populations and plant succession.5 An excellent survey of literature pertaining to strand and salt marsh vegetation in Oregon has been recently completed by McDonald and Barbour.8 The West Island Setting The Nehalem salt marshes occur within the river estuary as islands and land-tied units (Figure 1). Diking for dairy pasturage has reduced the area of marshland, especially to the east of the main channel, but aside from some grazing on Lazarus Island prior to 1952 and occasional deposition of debris associated with watershed logging, a nearly pristine condition still exists. West Island, with an area of 2.5 km2, is the largest of the marsh units. Casual observation suggests that its marsh vegetation closely resembles that of the other marshes. 3 H. D. House, "Vegetation of the Coos Bay Region, Oregon," Muhlenbergia (spring, 1914), pp. 81-100. * C. L. Johannessen, "Shoreline and Vegetation Changes of Estuaries," in Some Recent Physical Changes of the Oregon Coast, S. N. Dicken, ed. (University of Oregon, Department of Geography, final report on Office of Naval Research Contract Nonr 277104 Project NR 388-062, 1961), pp. 100-140. See ako C. L. Johannessen, "Marshes Prograding in Oregon: Aerial Photographs," Science (December 18, 1964), pp. 1575-1578. " M. W. Stock, "Biological Studies of Saldula palustris (Douglas) with Emphasis on Factors Influencing Wing Pigmentation (Heteroptera: Saldidae)," unpublished doctoral dissertation, Oregon State University, 1972; K. B. McDonald , "Quantitative Studies of Salt Marsh Mollusc Faunas from the North American Pacific Coast," Ecological Monographs (spring, 1969), pp. 33-59; Carol Jefferson, "Plant Communities and Succession in Oregon Coastal Salt Marshes," unpublished doctoral dissertation, Oregon State University, 1975. • K. B. McDonald and M. Barbour, "Beach and Salt Marsh Vegetation of the North American Pacific Coast," in Ecology of Halophytes, R. J. Reimold and W. H. Queen, eds., (New York: Academic Press, 1974), pp. 175-233. YEARBOOK VOLUME 38 1976 21 NEHALEM MANZANITA "T^F"^ MOHLER DEAW OiMARSH WESTiI fiat ISL. "baleni WHEELER BRIGHTON OREGON Figure 1. Nehalem...