Determinants of Pattern in a New England Salt Marsh Plant Community

Abstract

In New England salt marshes, Spartina alterniflora dominates the low-marsh habitat, which is covered daily by tides. The high-marsh habitat, which is not flooded daily, is dominated on its seaward border by Spartina patens, and on its terrestrial border by Juncus gerardi. Each of these vegetation zones has a characteristic suite of physical factors associated with differences in tidal inundation. In particular, substrate redox increases and salinity decreases with increasing marsh elevation. Although correlations between physical factors and the occurrence of specific marsh plants have been suggested to be causal, a 5-mo transplant experiment suggested that the distribution of perennials across the marsh does not correspond to their potential performance across the marsh in the absence of surrounding vegetation. While the high-marsh perennials appear to be restricted to the high-marsh habitat by harsh physical conditions in the low-marsh habitat, the lowmarsh dominant, S. alterniflora, is capable of vigorous growth across the entire marsh and appears to be excluded from the high-marsh habitat by the high-marsh perennials.Throughout the high marsh, two other plant species, Distich/is spicata and Salicornia europaea, are found associated with areas that have been disturbed recently. Physical disturbance, in the form of mats of dead plant material (wrack) rafted by tides onto the marsh, is most severe in the spring and early summer, and decreases with increasing marsh elevation. Differential plant mortality results from short-term disturbance events. D. spicata and S. alternif/ora are more tolerant of wrack burial than are the other marsh plants, and short-term disturbance increases the relative abundance of these species in the community. Longer lasting disturbance events kill all the underlying vegetation, leaving discrete bare patches throughout the high marsh. D. spicata rapidly colonizes these patches with vegetative runners, while S. alternif/ora and Sa. europaea recruit to these patches by seed. The relative abundance of these plants in recently created bare patches exceeds greatly their relative abundance in the surrounding vegetation. Over time, however, these early colonizers are overgrown and displaced in high-marsh patches by S. patens and J. gerardi, which grow slowly, as dense turfs of roots, rhizomes, and tillers.Physical disturbance and interspecific competition appear to be major determinants of the spatial pattern of marsh plant communities. These processes will need to be considered in relation to edaphic factors in elucidating the underlying mechanisms of salt marsh plant zonation.

Mechanisms of exclusion of native coastal marsh plants by an invasive grass

“…The plants in the marsh are typical of brackish and salt marshes of southern New England, with characteristic bands of perennial turf-forming grasses and rushes along a gradient of elevation (e.g. Niering & Warren 1980;Bertness & Ellison 1987;see Tiner 1987 for taxonomic authorities). The banks of tidal creeks and the low marsh are dominated by the grass Spartina alterniflora .…”

“…Floating plant litter, or wrack, is common in these coastal marshes (primarily the grass S. alterniflora, but also Phragmites), and forbs commonly find refuge in bare patches that are generated where wrack stranded in the open marsh smothers native marsh turf, but is subsequently removed by the tides (Bertness & Ellison 1987;Ellison 1987;Brewer et al 1997;Minchinton 2002a). The residency time of litter within stands of Phragmites appears to be much longer than that which typically produces bare patches in the open marsh, and few plants establish in the marsh where wrack remains in place (e.g.…”

Rapid shoreward encroachment of salt marsh cordgrass in response to accelerated sea-level rise

“…Lower species borders are controlled by physical stress tolerance to flooding and soil anoxia, whereas upper species borders are controlled by interspecific plant competition (9,10). Marsh hay and spike grass are excluded from the low marsh by low substrate oxygen levels.…”

Marine ecological research in seashore and seafloor systems:accomplishments and future directions

“…Since species and populations are the essential currency of applied ecology and the grist of evolution, future research is needed to bridge this gap from the qualitative to the quantitative. Furthermore, innovations to our understanding of the generation of population and even community dynamics can come from studies relating individual behavioral or physiological responses to environmental forcing: rarely do such studies make the connections between the individual and the population, despite a potential for enhancing predictive capacity by uncovering the underlying mechanisms for population and community change (Bertness 1992, Wootton 1993, Micheli 1997.…”