Salinity and the small-scale distribution of three barrier island shrubs

Abstract

The importance of salinity to small-scale distribution patterns was examined for three shrubs common on barrier islands of the southeastern United States. Field measurements focused on the salt marsh – upland interface zone on Hog Island, Virginia, where Myrica cerifera, Baccharis halimifolia, and Iva frutescens form distinct distributional zones. Although considerable variation in salinity occurred throughout the growth season (June through October), total soil chlorides and groundwater salinity were lowest for M. cerifera, intermediate for B. halimifolia, and highest for I. frutescens. All three species showed similar diurnal and seasonal patterns in stomatal conductance and leaf xylem pressure potential, despite the differences in salinity. However, a laboratory experiment revealed interspecific differences in water relations when the three shrubs were exposed to identical salinity regimes. The field data and water relations experiment indicated M. cerifera is least tolerant to salinity, I. frutescens is most tolerant, and B. halimifolia is intermediate. Seed germination experiments revealed a similar response, except that B. halimifolia was more sensitive to salinity than M. cerifera. The interspecific differences in soil and groundwater salinity, along with the physiological response differences, indicated that salinity may be one of the major environmental factors influencing zonation among the three shrubs; however, the absence of I. frutescens and B. halimifolia in low salinity areas implied that other factors also influence zonation patterns on barrier islands. Key words: Baccharis halimifolia, Iva frutescens, Myrica cerifera, barrier island, salinity tolerance, shrub.

Freshwater and saltwater flooding response for woody species common to barrier island swales

“…All five woody species are common on Atlantic coast barrier islands and in coastal areas (McCaffrey and Dueser 1990, Stalter and Odum 1993, Young et al 1994. Myrica cerifera is frequently the dominant woody shrub in barrier island swales (Ehrenfeld 1990, McCaffrey andDueser 1990) and is considered relatively salt intolerant (Sande and Young 1992, Young et al 1994.…”

“…Myrica cerifera is frequently the dominant woody shrub in barrier island swales (Ehrenfeld 1990, McCaffrey andDueser 1990) and is considered relatively salt intolerant (Sande and Young 1992, Young et al 1994. Iva frutescens, a halophyte, occurs most frequently at the interface between the high marsh and terrestrial systems (Bertness et al 1992).…”

“…Iva frutescens, a halophyte, occurs most frequently at the interface between the high marsh and terrestrial systems (Bertness et al 1992). Baccharis halimifolia is frequently intermediate and often overlapping in distribution between M. cerifera and I. frutescens (Dueser et al 1976) and is also considered intermediate in tolerance to soil salinity and groundwater salinity (Young et al 1994). Pinus taeda is among the first tree species to invade barrier island swales in North Carolina (Stalter and Odum 1993) and is considered sensititve to long-term freshwater and saltwater flooding (Conner and Askew 1992, Pezeshki 1992, Johnson and Young 1993.…”

“…A sample size of n=5 per treatment ensm'ed that no plants were sampled on two successive dates. Cuttings used in determining the xylem pressure potentials were retained for tissue chloride analysis by hot water extraction (Young et al 1994). Baccharis halimifolia and I. frutescens had too few leaves to allow destructive sampling necessary for xylem pressure potential measurements.…”

Evolution of a freshwater barrier-island marsh in coastal Georgia, USA

“…An understanding of these and other long-term controlling factors, and the documentation of specific wetland responses to particular biotic and abiotic processes, should provide for more comprehensive wetland management programs and may help predict responses of specific wetland systems to future environmental perturbation (e.g. climate or sea-level changcL Many ecological investigations of coastal wetlands in the southeastern United States have focused on the relationships between plant distribution, salinity gradients, hydroperiod, and flooding (e.g.. Young et al, 1994, Perry and Atkinson 1997, Tolliver et al 1997, The responses of plant taxa to these local environmental parameters provides a theoretical basis for interpreting paleoecological records and assessing factors affecting past vegetational change. Pateoecological studies typically rely on stratigraphic sequences of pollen and macrofossil assemblages, and these changes may be compared with associated changes in charcoal, sedimentology, biogenic structures, and other fossil types (e.g., foraminifera, diatoms).…”