Effects of soil ph, redox potential, and elevation on survival of Spartina patens planted at a west central Florida salt marsh restoration site

Planting Spartina patens (Salt Meadow Cord Grass) is an integral part of restoring salt marshes along Tampa Bay, Florida, USA. Of the salt marsh species that are planted, S. patens often has the lowest survivorship. State managers have hypothesized that this low survivorship is related to transplant shock and to acidic soil conditions commonly found under dense stands of Casuarina sp. (Australian Pine), an exotic invasive. This study documents planted S. patens health and survivorship over 11 months at a restoration site previously dominated by Casuarina sp. Three plots of 100 plants each were established in varying soil pH, with each plot covering above and below the recommended elevation range for S. patens. Transplant shock occurred within the first thirty days after planting and affected overall survival. Spartina patens survival was not affected by soil pH (p = 0.827) as evidenced by the presence of healthy individuals outside the plots, in soil pH ranging from 4.76 to 8.94. However, there was a sharp decline in plant health when redox potentials fell below -50 mV. Although elevation and redox potential were highly correlated (p < 0.001, R-2 = 0.736), plant health varied more with elevation (p < 0.001, R-2 = 0.387) than redox potential (p < 0.001, R-2 = 0.950), suggesting that elevation, while a good coarse predictor of site suitability, may not always be the best measure. Redox potential should be monitored, in addition to measuring elevation, to avoid planting in highly reduced areas. Furthermore, adjusting the lower limit of the target elevation range to a higher elevation will increase the amount of survivorship.