Ask Mr. Smarty Plants

Under normal circumstances, Galveston Island's sandy porous soil functions as an aquifer containing a zone of freshwater.  This "lens" of fresh water derives from rainwater that infiltrates through the soil and overlies a deeper zone of seawater that infiltrates laterally from the ocean and bay.  Some of the saltwater that covered the island during Hurricane Ike no doubt also filtered downward and is now above the freshwater lens.  Saltwater is denser than freshwater and so will move downward and mix with the freshwater.  The saltwater will eventually become thoroughly diluted.  In addition, the layer of mixed water will also be diluted by rainwater seeping downward through the soil.  How long that will take will depend on the amount of salt water from the hurricane and how much rainwater infiltrated.  Additionally, some of the island is built on clay deposits that are far less porous, and mixing in these areas may take longer. So, eventually Galveston Island's soil will have no trouble supporting the transplanted replacement trees—hopefully, sooner than later.  Of course, many of the plants on Galveston Island are salt tolerant.  This is quite evident since Galveston has been hit many times over the centuries by hurricanes bringing elevated salt concentrations but the island still has abundant plant life.