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Biological Communities: Coastal Dunes

Coastal Dunes
I. Climatic and Geologic Setting of Coastal Dune Communities

Plant communities along the California coastline have been subject to vastly fluctuating physical and climatic changes. Sixty-five million years ago (mya), the coastal climate and flora changed from subtropical to increasingly seasonal, i.e. dry summers and cold winters. By 8 mya the California Current had cooled and was producing fog banks, summer high pressure zones blocked storms from the north as well as tropical storms from the south, summer precipitation decreased and a Mediterranean climate prevailed (Wilken 1993). The ice age which began 2.4 mya brought about 48 warm-cold cycles (Schaffer 1993) with fluctuating sea levels pushing beaches back and forth. During the most recent cold event, the Tioga (20,000 years ago), conifers were dominant and widespread along the coast, and species which are now rare were probably common, e.g. cypresses, Santa Lucia fir, and Monterey, Torrey and Bishop pines. Warming since then has isolated conifers at higher elevations and at disjunct locations along the coast, including 4 rare species on the Monterey Peninsula alone. Concurrently, beaches have migrated significantly landward in response to a sea level rise of 120 meters.

Monterey Bay is the widest opening to the sea on the Pacific coast of the United States (Cooper 1967). Pleistocene and more recent winds drawn into that opening accumulated sands into the Monterey dunes, northernmost of the state's four major coastal dune complexes, including all of Fort Ord (ibid).

This section will describe the communities occurring from high tide to marine-influenced habitats on terrestrial soil. The coastal dune beach plant community (Barbour and Johnson 1988), also called the active coastal dune (Holland 1986) is the only vascular plant community at the shoreline, i.e. subject to the constant and direct rhythms of wind and tide. Three other dune communities also occupy coastal sands. In addition, two types of coastal plant communities live on terrestrial soils of coastal slopes: scrub and closed-cone forest. Coastal plant communities are described by Munz and Keck (1968), Mayer and Laundenslayer (1988) and systematically by Holland (1986) and Sawyer and Keeler-Wolf (1995). Most of these communities are designated as rare and/or vulnerable (California Department of Fish and Game 1994). See Table 1 for scientific names of species noted.

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