RESPONSE OF MARINE DELTAIC SURFACES TO MAJOR EARTHQUAKE UPLIFTS IN SOUTHCENTRAL ALASKA

Major earthquake uplifts in south-central Alaska of marine deltaic surfaces to an inter-tidal or supra-tidal status cause drastic shifts in processes and vegetation. To assess long-term ecosystem changes as a deltaic landscape converted from a tidal marsh to a supra-tidal wetland, we studied a four-stage chronosequence of deltaic surfaces (30-yr-old inter-tidal surface, 352-yr-old inter-tidal surface, 30-yr-old supra-tidal surface, and 280-yr-old supra-tidal surface). Plots were used to gather landform, soils, and vegetation information, and landform schematics and aerial photo interpretation were used to determine their spatial distribution. Succession progressed on inter-tidal surfaces from pioneer species (principallyCarex lyngbyaei) on newly uplifted mud flats, to a mature tidal marsh with channels, levees, and basins dominated byCarex lyngbyaei with thick root mats. Uplift of the mature tidal surface to a supra-tidal status allowed freshwater tolerant species (Equisetum fluviatile, Sphagnum spp.) to invade the basins, and trees and shrubs displaced herbaceous vegetation on levees. On the oldest supra-tidal surface, basins developed peatlands (Andromeda polifolia, Sphagnum spp.), and pH decreased. Levees supported trees or shrubs on mineral or peat soils. Vegetation zonation within a basin-levee complex was evident and repeated, with some variation, across the surfaces. At the landscape scale moving inland, gradients in vegetation occurred on all surface ages.