Nitrogen addition could shift plant community composition in a restored California salt marsh

At a salt marsh restoration site, fertilizer trials to improve height growt h of Spartina foliosa (a C-4 perennial grass that can reach 140 cm) appeare d to favor Salicornia bigelovii (an annual C-3 succulent under 40 cm tall) where the two species co-occurred on the marsh plain. This observation prom pted a field experiment to examine the potential for nitrogen (N) addition to shift community composition. Without N addition, total stem length and s tem density of S. foliosa did not respond to the presence or absence of S. bigelovii. But where N was added, S. foliosa growth increased only where S. bigelovii was removed from plots. S. bigelovii responded strongly to ferti lizer, with mean heights matching those of S. foliosa and 600% increases in biomass, branching, and seed production (to more than 1 million seeds/m(2) ). Soil N also increased seasonally where S. bigelovii was present, suggest ing that this species may aid accumulation of N at restoration sites with p oor soils. S. foliosa growth is greatest at lower elevations along tidal cr eeks where it occurs alone. Beyond creek edges, where S. bigelovii and othe r potential competitors occur, S. foliosa is unlikely to grow tall even wit h N addition. Thus, there is little point in trying to force mixed-species stands to provide tall S. foliosa for nesting by an endangered bird, Rallus longirostris levipes (the Light-footed Clapper Rail). A marsh construction design that maximizes tidal creek edges is thus recommended when restorati on goals include providing habitat for clapper rails.