The roles of seedling salt tolerance and resprouting in forest zonation on thewest coast of Florida, USA

To determine whether the zonation of seven coastal tree species in north Florida correlated with the relative abilities of their seedlings to tolerate soil salinity, we subjected seedlings of Sabal palmetto, Juniperus virginiana var. silicicola, Quercus virginiana, Celtis laevigata, Ulmus spp., Acer floridanum, and Liquidambar styraciflua to a range of salinities (～0, 2, 4, 8, 15, and 22 g synthetic sea salt/L; up to 63% full strength seawater salinity) in a 6-mo greenhouse experiment. Pots with shoot-killed plants were flushed with freshwater for ≥5 wk to assess recovery. Salt tolerance was assessed as plant survival under saline conditions and as the ability to retain green leaf tissue under saline conditions. Using either criterion, the rank order of seedling salt tolerance correlated significantly (P ≤ 0.05) with that expected based on species zonation near the coast. Agreement was better, however, using retention of leaf tissue as an index of salt tolerance. Species from forest zones that were frequently exposed to tidal water retained green leaf tissue under saline conditions. Species from zones occasionally subjected to very high tides were shoot killed but resprouted following removal of salt from the root zone. Those restricted to zones exposed only to infrequent storm surges died at salinities ≥4 g/L. Thus, differential seedling salt tolerance was consistent with tree zonation and, although the ability of young seedlings to resprout following salt removal did not appear to allow tree establishment at the extreme seaward margin of the forest, it appeared important in intermediate zones.