In areas where the soil contains an abundance of silt, oak-hickory forests predominate. Where the soil is sandy and porous, pine barrens woodlands occur. The species makeup of these forests vary greatly, and in many places these forest types intergrade. In protected areas within the intertidal zone along the shore, salt marshes form in the intertidal zone. On the South Shore, this protection is offered by barrier beaches, while on the North Shore, it is provided by natural harbors.
Wind creates large sand dunes on the barrier beaches.
Here, the morphology of the vegetation is strongly controlled by the wind. Three major aquifers lie beneath Long Island's surface, and together, contain about 60 trillion gallons of groundwater. The aquifers are supplied with water by precipitation. Where Long Island's surface is low enough in elevation to penetrate the water table, bodies of fresh water, such as ponds, streams, marshes and bogs occur. Groundwater exits the aquifer system through evaporation, stream flow and subsurface seepage into the surrounding salt water.