A 5‐yr Record of Aerial Primary Production and Stand Characteristics of Spartina Alterniflora

Abstract

The purpose of this paper is to document and explain the interannual variability in aboveground primary productivity from salt marshes at North Inlet, South Carolina. A census method of measuring production was applied to salt marsh sites vegetated by the grass Spartina alterniflora, and a statistically significant relationship between stem age and cumulative leaf loss was used to estimate leaf turnover. Aboveground productivity was 2.3 times as large as the positive increment in standing biomass density due to the turnover of stems and leaves, with stem turnover accounting for 33% and leaf turnover 23% of total aboveground productivity. A numerical simulation demonstrated the sensitivity of destructive harvest methods to sampling errors that are propagated by spatial variability. Monthly measurements, made at one site for >5 yr, document a twofold variation in annual aboveground production, which has important implications for the biogeochemistry and trophic dynamics of estauries. Positive correlations indicate that mean sea level and/or rainfall are important determinants of annual production, and their effect on sediment salinity is postulated to be the proximate determinant of interannual variation in production. Monthly growth rates and standing biomass densities from two different marshes, both situated at the mean high tide elevation, have been equivalent for 3 yr despite a consistent twofold difference in stem density. Thus, equivalent aboveground productivity was maintained in populations differing in their allocation of photosynthate between stem growth and asexual reproduction.