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Title: Phytosociology and succession on earthquake-uplifted coastal wetlands, Copper River Delta, Alaska.

Author: Thilenius, T.F.;

Date: 1995

Source: Gen. Tech. Rep. PNW-GTR-346. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 58 p

Publication Series: General Technical Report (GTR)

Description: The delta formed by the Copper River stretches more than 75 kilometers along the south-central coastline of Alaska. It is the terminus of the outwash deposits from a large part of the most heavily glaciated region of North American, and all major rivers that flow into the delta carry extremely high levels of suspended sediments. Coastal wetlands extend inland for as much as 20 kilometers. In 1964, an earthquake of Richter Scale 8.4 to 8.6 raised the entire delta from 1.8 to 3.4 meters above the previous mean sea level. Subtidal areas became intertidal, and intertidal areas supertidal. Marshland advanced seaward as much as 1.5 kilometers in the intertidal zone. Vegetation on many, but not all, newly supertidal levees began to change from herb to shrub. A change in frequency and duration of tidal inundation and water salinity has been thought to be the most obvious cause of this succession, but explanation is lacking. Fresh water dominates the estuarine circulation as a result of a bar-built estuary and the extremely high input of fresh water from glacier runoff and precipitation. Tides merely raise fresh water onto the wetlands. Halophytes are rare even at the seaward edge of vegetation. The characteristic species of the present intertidal marshes, Carex lyngbyei, also is characteristic of inland freshwater marshes. lnitial postearthquake invasion of woody plants was confined to natural levees. More recently, shrubs have begun to move seaward into new intertidal marshland and into supertidal interlevee basins. Current plant communities on new marshland (tidal) are Carex C-T (low marsh); Carex C-T (high marsh); Carex/Potentilla C-T (low levee); and Myrica/Carex-PotentiIla C-T (high levee). On old marshland (nontidal) the current plant communities are Alnus/Myrica-Salix/Carex C-T (foreshore levee); Myrica/Carex- Calamagrostis (foreshore levee); Carex/Equisetum-Lathyrus C-T (interior levee); Carex/Lathyrus C-T (moderately hydric interlevee basin); and Carex-Cicuta/C-T (hydric interlevee basin). Vegetation analogous to that developing on supertidal levees and basins is present on older wetland habitats further inland. Likely, the same plant successions would have occurred without an uplift. The uplift appears to have altered locations and rates, but not the nature, of wetland plant succession on the Copper River Delta.

Keywords: Copper River Delta, plant ecology, plant succession, tidal marshlands, tectonic uplift, Alaska

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Thilenius, T.F. 1995. Phytosociology and succession on earthquake-uplifted coastal wetlands, Copper River Delta, Alaska. Gen. Tech. Rep. PNW-GTR-346. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station. 58 p

 


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