Growth of Spartina alterniflora within native and transplant-established stands on the upper-Texas Gulf Coast

Abstract

Change in culm density and end of season above- and below-ground biomass were monitored within a native seedling stand of Spartina alterniflora. Annual trends in culm density, culm height, and above- and below-ground biomass were documented at four elevations within an established S. alterniflora marsh. Effects of two fertilizer rates and a commercial root dip treatment were studied on the survival and growth of three S. alterniflora culm types (native seedlings, high elevation dwarf-form, and low elevation tall-form) when transplanted within two soil conditions at a common elevation. All studies were located within a natural salt marsh complex at the southeastern tip of the Bolivar Peninsula, Galveston County, Texas. Density of native seedlings decreased approximately 50% between germination in January and February and late April. Tiller production was then initiated, and culm densities increased from 13 to 40-fold during the remainder of the first growing season. Culm density and high and biomass (above- and below-ground) varied according to changes in substrate elevation and with the presence of a surface silty-clay substrate layer. Culm density and height were less, but were more uniform within the stand at the end of the second growing season than at the end of the first. Culm density within the established S. alterniflora marsh was not strongly associated with substrate elevation. However, culm height and above-ground biomass tended to decrease as elevation increased and to be greatest at the lowest elevation. Below-ground biomass (culm bases, roots, and rhizomes) was not as strongly associated with elevation. Live above- and below-ground material was present throughout the year. Peak standing crop of both categories occurred in mid summer. Large quantities of dead material were present throughout the year. Root-rhizome: shoot ratios increased as elevation increased. The commercial root dip treatment had devastating effects on transplant survival of the seedling, dwarf-form, and tall-form culm types. Fertilizer treatments did not significantly affect culm survival, vegetative reproduction, or end of growing season biomass parameters...