The challenge of restoring vegetation on tidal, hypersaline substrates

Hypersaline tidal wetland restoration sites are challenging to vegetate, and the specific factors responsible for transplant mortality are difficult to pinpoint. Two southern California sites (Tidal Linkage and Friendship Marsh), planted as large field experiments, had differential transplant survival (93% for a 1997 planting at the first site, and 10% for a 2000 planting in the second site). Multiple stresses (high salinity, sediment deposition, algal smothering and animal activity) are implicated as the cause of mortality in the experimental plantings. Greater hypersalinity and sedimentation appeared to be a function of site context, with greater sediment inflows and salt concentration over the larger (8-ha) marsh plain at the Friendship Marsh. Species differed in establishment rates among sites and years; the regional dominant, Salicornia virginica, performed best as a transplant and in volunteer seedling recruitment in the Tidal Linkage; hence, it was not planted at the larger site, where it has recruited without assistance. Frankenia salina had high survival in the 2000-2001 plantings; this species is also widespread in the region. Our attempts to restore salt marsh plain vegetation in Southern California led to greater appreciation of the importance of environmental stress and stochastic events and their potential for interaction. Hypersalinity and other factors are extremely difficult to ameliorate, especially in large restoration sites.