Plant zonation in low‐latitude salt marshes: disentangling the roles of flooding, salinity and competition

Abstract

Summary 1We investigated the factors producing zonation patterns of the dominant plants in south-eastern USA salt marshes where Juncus roemerianus dominates the high marsh, and Spartina alterniflora the middle and low marsh. 2 Juncus did not occur naturally in the Spartina zone and performed poorly when transplanted there, irrespective of whether neighbours were present or removed, indicating that its lower limit was set by physical stress. 3 In contrast, although Spartina occurred naturally at low densities in the Juncus zone, it performed well if transplanted there only if neighbours were removed, indicating that its upper limit was set by competition. 4 Parallel laboratory and field manipulations of flooding, salinity and competition indicated that the lower limit of Juncus was mediated by both flooding and salinity, but not by competition. 5 The general mechanisms producing zonation patterns of vegetation in coastal salt marshes may be universal, as suggested by previous studies, but the importance of particular factors is likely to vary geographically. In particular, salinity stress probably plays a much more important role in mediating plant zonation patterns at lower latitudes. 6 Our results suggest that the nature of ecological interactions is likely to vary geographically because of variation in the physical environment, and this variation must be taken into account in order to successfully generalize the results of field studies across geographical scales.

Salt marsh ecohydrological zonation due to heterogeneous vegetation–groundwater–surface water interactions

“…(3) Intertidal salt marshes exhibit pronounced vegetation zonation, with plant assemblages configured into visually obvious spatial patterns. This vegetation zonation is partially related to patterns of soil water availability or excess [Chapman, 1938a[Chapman, , 1938bMahall and Park, 1976b;Cooper, 1982;Pennings and Callaway, 1992;Silvestri et al, 2005;Varty and Zedler, 2008], among other causes including interspecific interactions and variations in nutrients, soils, salinity, tidal exposure, and disturbance [Bertness et al, 1992;Pennings and Callaway, 1992;Emery et al, 2001;Pennings et al, 2005;Forbes and Dunton, 2006]. Interestingly, these three features of salt marsh plant-water relations have not yet been combined nor integrated with physics-based models of intertidal hydrology.…”

Spartina alterniflora with high tolerance to salt stress changes vegetation pattern by outcompeting native species

“…Inundation and salinity are two major nonresource conditions in salt marshes (Emery et al 2001, Pennings et al 2005, Silvestri et al 2005. Many studies have shown that P. australis and S. alterniflora have a high tolerance to the anoxia caused by inundation (Maricle and Lee 2002, Wang et al 2006a, b, Engloner 2009).…”

Phylogenetic relatedness, ecological strategy, and stress determine interspecific interactions within a salt marsh community

“…Salinity stress is one of a number of important factors limiting the distribution and diversity of species within coastal marshes (Bertness et al 1992;Bertness and Hacker 1994;Hacker and Bertness 1999;Pennings et al 2005). Although the salinity responses of only a few pairs of species supported the SGH in this study, the effect of salinity on species interactions is clear.…”