Effects of wrack burial in salt-stressed habitats: Batis maritima in a southwest Atlantic salt marsh

In coastal salt marshes, mars of wrack (dead plant stems) that are deposite d on the marsh by high tides can kill underlying vegetation and initiate se condary succession. The importance of wrack disturbance in northwest Atlant ic salt marshes has been a topic of recent debate. The importance of wrack disturbance in southwest Atlantic salt marshes, which experience a very dif ferent climate regime than do northern marshes, has rarely been examined. W orking in a Georgia salt marsh, we documented a pattern of positive associa tion between wrack and Batis,maritima biomass: and conducted experiments th at indicated that wrack was beneficial to Batis maritima. Sampling indicated that natural wrack deposition was correlated with areas of vigorous Batis growth and mild soil conditions. Natural wrack deposition occurred primarily at the highest elevations occupied by Batis maritima (t he high Batis zone). Batis plants in the high zone were taller: with more a nd larger leaves. and contained several times the biomass/unit area than Ba tis plants at lower elevations. High zone soils had lower salinities, bette r percolation rates, and a lower organic content than did soils from lower elevations. Experimental manipulations demonstrated that deposition of wrac k was partially responsible for these patterns. In each of two experiments: soil salinities were lower and plants taller and larger in the presence of wrack compared to in its absence. Although wrack lowered salinities and en hanced plant growth, the effects were not large enough to completely explai n the differences between Batis zones. Instead, wrack probably reinforced p re-existing gradients in flooding and salinity caused by differences in ele vation and terrestrial runoff. Our results contrast with previous studies from northern marshes. Because o f geographic differences in climate and plant phenology, northern marshes a re more likely than southern marshes to receive patches of wrack thick enou gh to kill underlying vegetation. Plants covered by thin layers of wrack, a s commonly occurs in southern marshes, may often grow through the wrack rat her than suffer mortality. Also because of climatic differences, wrack is m ore likely to benefit plants by ameliorating salinity stress in southern ma rshes, where soil salinities are often hypersaline, than in northern marshe s where soils are rarely hypersaline. Although ecological processes may dif fer between northern and southern salt marshes, these differences may be pr edictable based on an understanding of geographic variation in climate.