Plant zonation in an Alaskan salt marsh. I. Distribution, abundance and environmental factors

(1) Patterns of plant species distribution, plant abundance, and environmental factors on Susitna Flats, an Alaskan subarctic salt marsh, are described. (2) Eight vegetation zones were recognized along a transect from the Cook Inlet shore to the inland shrub boundary. Peak above-ground standing crop (dry weight) ranged from a minimum of 50 g m-2on outer mudflats sparsely covered with Puccinellia nutkaensis to a maximum of 466 g m-2in more inland, waterlogged areas dominated by the sedge Carex lyngbyaei. (3) A few species, including Triglochin maritimum and Potentilla egedii, occurred over the entire range of altitude and environmental conditions. Most species were more narrowly distributed, giving rise to the zonation pattern. (4) Although there was little topographic relief and soil texture was similar throughout the Flats, the vegetation zones differed with respect to flooding frequency, rate of siltation, soil organic content, moisture content, redox potential, and salinity. In particular, combinations of soil salinity and waterlogging segregated most of the vegetation zones. However, we cannot conclude from these correlations that edaphic factors determine plant zonation.