Spatio-temporal dynamics of the invasive plant species <i>Elytrigia atherica</i> on natural salt marshes

Question In the past decades, the tall native invasive grass, Elytrigia atherica, has been increasing in frequency and dominance on salt marshes along the Wadden Sea coast. Is this rapid expansion an outcome of natural succession or is it driven by anthropogenic eutrophication resulting from atmospheric deposition? Location Salt marshes on four back-barrier islands, Wadden Sea on the coast of the Netherlands and Germany. Methods We used a combination of time series of vegetation maps and chronosequence data of four naturally developed salt marshes to address our questions. These salt marshes have not been grazed by livestock or subject to other management regimes. By comparing development within and between four different salt marshes, we were able to study the spatial and temporal dynamics of the community dominated by E. atherica on natural salt marshes. Results The expansion rate of the E. atherica community was highest on young salt marshes (up to 30yr old) with vertical accretion rates of 0.35cm center dot yr1. The rate of expansion decreased on older marshes and the direction reversed, becoming negative, on the oldest marshes (around 90yr old), which have no vertical accretion and are under waterlogged conditions. Conclusions The expansion of E. atherica on natural, back-barrier islands along the Wadden Sea coast is more influenced by the age of the salt marsh and patterns in vertical accretion of soil than by uniformly spread atmospheric deposition.