Plant zonation at salt marshes of the endangered cordgrass Spartina maritima invaded by Spartina densiflora

Abstract

The South American cordgrass Spartina densiflora is invading European salt marshes getting into contact with the indigenous and endangered lowmarsh dominant, Spartina maritima. This work describes the evolution of the plant zonation during 7 years in a marsh of S. maritima invaded by S. densiflora. S. maritima appeared throughout the whole intertidal gradient from 1.72 to 3.33 m over Spanish Hydrographic Zero (SHZ), showing its higher biomasses and shoot densities at low elevations. In contrast, S. densiflora only invaded upper areas ([+2.59 m SHZ) at the centre of circular tussocks of S. maritima. Above-ground biomass of S. maritima dropped drastically at maximum occupation of space by the alien, and its shoot density and above-ground biomass decreased at S. densiflora zone during the study. The competitive potential of S. densiflora was reflected in high above-and below-ground biomass and shoot densities, accompanied by elevated wrack accumulation and the absence of other marsh plants presented together with S. maritima from areas dominated by S. densiflora. S. densiflora altered the native vegetational zonation pattern through the invasion of the centre of S. maritima tussocks; however, the alien invasion may be limited by the presence of the autochthonous cordgrass at lower elevations.

Cordgrass Biomass in Salt Marshes

“…As we have shown above cordgrass above-ground biomass accumulation depends on clone architecture and shoot morphology. These traits show high intraspecific variation as described for S. alterniflora (Lessmann et al, 1997;Proffitt et al, 2005), S. densiflora (Nieva et al, 2001a;Castillo et al, 2008b), S. maritima (Sanchez et al, 1997;Castellanos et al, 1998;Otero et al, 2000;Castillo et al 2005a;Castillo et al, 2008a,b) and S. patens (Silander & 7 Antonovics, 1979). Intraspecific changes in growth form may be based on phenotypic plasticity or genotypic differences.…”

“…400-600 g DW m -2 in low salt marshes (with ca. 6000-7000 shoot m -2 ) (Nieva et al, 2001a;Castillo et al, 2008b) since S. densiflora is quite sensitive to long flooding periods (Castillo et al, 2000). In high marshes, S. densiflora accumulates intermediated biomass values between low and middle marshes (ca.…”

“…In addition, mature tussocks of S. densiflora normally to show elevated wrack accumulation (ca. 800 g DW m -2 ) (Castillo et al, 2008b). Wrack accumulation may interfere with other species colonization of inner areas of Spartina clumps.…”

“…Following the general theory of salt marsh zonation (sensu Callaway, 1992 andPennings et al, 2005): competitive dominants colonize higher elevation in the tidal frame displacing competitive subordinates to more stressful environments with long submergence periods or higher salinities. For example, invasive cordgrass such as S. alterniflora, S. densiflora and S. patens may displace indigenous cordgrasses (SanLeon et al, 1999;Chen et al, 2004;Castillo et al, 2008b). The outcome of competitive interactions changes depending on the abiotic environment.…”

Wrack burial reduces germination and establishment of the invasive cordgrass Spartina densiflora

“…(Poaceae) is invading salt marshes in southern Europe, Northwest Africa and the West Coast of North America (Bortolus 2006). In invaded marshes, S. densiflora develops very dense populations where large amounts of dead matter are deposited (Nieva et al 2001;Castillo et al 2008). Moreover, S. densiflora seeds float so they are dispersed by currents and tides together with plant debris (Howard and Sytsma 2013).…”