Nucleation and Facilitation in Saltmarsh Succession: Interactions between Spartina Maritima and Arthrocnemum Perenne

Abstract

1 The construction of a raised dike across the coastal saltmarshes of Odiel (Huelva, south-west Spain) in 1977 divided a uniform area of low-lying sediment into two lagoons with very different drainage properties. To the east of the dike, there is rapid drainage into the estuarine channel of the Odiel and Tinto rivers, whereas to the west, the development of sand spits has impeded drainage such that standing water persists long after high tides, despite the slightly higher elevation of this area. 2 Both lagoons have been colonized by isolated clones of Spartina maritima, which have locally enhanced accretion to form domed tussocks (`nucleation'). The diameter of the tussocks was highly correlated with the elevation of their sediment surface, the larger tussocks having been the earlier colonists in a generally accreting system. Spartina in the interior of the tussocks showed reduced tiller density and vigour. 3 Only in the better-drained lagoon have the central, higher areas of the Spartina tussocks been invaded by Arthrocnemum perenne, although seed is freely available in both lagoons. Arthrocnemum formed a sprawling, dense canopy and a superficial, relatively impenetrable root system; it rapidly suppressed the remaining tillers of Spartina, eventually leaving only a fringe around the edge of the tussock. Areas invaded by Arthrocnemum were characterized by a superficial layer (10 cm) of oxidizing sediment $(E_h > + 80 mV)$. Spartina-dominated areas in both lagoons remained highly reducing, even in the surface layers ($E_h < - 150 mV$). 4 In terms of successional mechanisms, primary colonization by Spartina maritima facilitates the invasion by Arthrocnemum, which only becomes established from seed on relatively well-drained, oxidising sediments. The interaction is, however, more complicated than this: declining tiller density within the tussocks prior to invasion by Arthrocnemum is consistent with an inhibition mechanism, and the superior competitive ability of Arthrocnemum, once established, suggests that a tolerance mechanism may also operate

Comparing biodiversity effects among ecosystem engineers of contrasting strength: macrofauna diversity in Zostera noltii and Spartina anglica vegetations

“…For example, ecosystem engineers may enhance diversity by facilitating the presence of other organisms or communities (e.g., Bruno et al 2003) which may eventually lead to succession (e.g., Castellanos et al 1994;Fogel et al 2004). Engineering species may also enhance diversity by causing spatial or temporal heterogeneity (e.g., excavations by pocket gophers, Reichman and Seabloom 2002; fungusgrowing termites, Jouquet et al 2004).…”

“…Spartina anglica is characterized by much taller and stiffer shoots and a larger above-ground biomass. Positive habitat complexity effects of Spartina on benthic assemblages may be counteracted by its effect on sediment properties, as Spartina forms well-defined dome-shaped tussocks (Castellanos et al 1994;Bouma et al 2007;van Hulzen et al 2007) with a relatively compact, densely rooted, well aerated, dry sediment (Van Wesenbeeck et al 2007). This effect on sediment properties may be expected to be more pronounced in mature Spartina marshes than in more recently established Spartina tussocks, as the latter will contain a lower shoot and root density.…”

Negative Plant–Soil Feedback and Positive Species Interaction in a Herbaceous Plant Community

“…The common 'phalanx' type growth strategy leads to densely aggregated clones with lower ramet density in the centre; a pattern referred to as fairy-ring or central die-back (Wikberg and Svensson 2003). The degeneration of the central area of the tussock has been interpreted as the results of the architectural development of the genet (Danin 1996), increase of interspecific competition inside the clones (Castellanos et al 1994) or, alternatively, as a consequence of changes in abiotic factors or resource levels (Falinska 1995;Wikberg and Mucina 2002). Plant-soil 'negative feedback' is a specific case of such plant-induced soil heterogeneity Bever 1994).…”

Self‐Organization and Vegetation Collapse in Salt Marsh Ecosystems

“…As a consequence, plant growth in salt marshes is characterized by positive, facilitative interaction, both among individuals (Bertness and Hacker 1994) and among species (Bertness and Shumway 1993;Bertness and Yeh 1994;Shumway and Bertness 1994). Many salt marsh plants strongly increase the deposition of clay, prevent sediment erosion by both waves and water currents (Yapp et al 1917;Castellanos et al 1994;Esselink et al 1998;Sanchez et al 2001), and ameliorate salinity levels (Bertness and Hacker 1994;Hacker and Bertness 1995;Srivastava and Jefferies 1995b). This in turn benefits the growth of the vegetation because salt stress and tidal currents are reduced by the increased elevation of the sediment relative to the average water level (Bertness et al 1992;Srivastava and Jefferies 1995a).…”