plants have various specialized adaptations for surviving substantial 

 periods of low moisture. The least tolerant stage lies between trans- 

 planting and the development of a new root system that is adequate to 

 extract moisture throughout a large volume of sand. Consequently, trans- 

 planting must be set deep enough for root development to occur before 

 complete drying. On most U.S. coasts, the sands are usually moist during 

 most of the recommended transplanting season; lack of moisture is a pro- 

 blem only in unusually dry seasons. 



Moisture content is more important in the gulf coast where tempera- 

 tures remain relatively high throughout most of the year, rainfall is 

 erratic, and evaporation rate exceeds precipitation. Dahl, et al. (1975) 

 found it necessary to irrigate fence-built dunes and other elevated areas 

 behind the backshore before planting, primarily to firm the sand, except 

 during and soon after heavy rains. They used sprinklers supplied by 

 water pumped from open-pit wells dug immediately behind the dune line. 

 Water was applied at the rate of about 0.5 centimeter per hour; it took 

 about a day to wet the sand to a depth of 15 centimeters. The ground 

 water was excessively saline at times but up to about 3 parts per thou- 

 sand was tolerated by the plants. 



Irrigation after planting is not generally worthwhile. Sand does not 

 dry rapidly below the 15-centimeter level and irrigation does not raise 

 the water table. Consequently, if the planting zone is moist from rain- 

 fall or preplanting irrigation, further watering adds little. Small-scale 

 plantings where intensive management is possible may justify irrigation of 

 the planting. Irrigation may be used under extreme drought conditions and 

 to leach out salt following inundation by saltwater. However, the plants 

 that are well adapted to the dune and beach environment, and have adequate 

 moisture at planting, usually grow and survive with little added help. 



Irrigation is sometimes the only way to firm the surface and prevent 

 dry sand from refilling holes or furrows before plants can be inserted. 

 Hand planting requires less than a 5-centimeter depth of dry sand but a 

 mechanical transplanter can operate through a layer twice as thick. When 

 the dry layer exceeds these limits, the only alternatives are to irrigate 

 or wait for rain. 



(2) Salinity . Salinity is a potential inhibitor to plant growth 

 along any seashore. Salt is deposited on beaches and dunes in substantial 

 quantities by salt spray or by flooding. 



Fortunately, the potential of salt damage to the establishment and 

 growth of dune plants is greatly tempered by the rapid leaching of the 

 dune sands. These sands have almost no retentive capacity for salt and 

 only a small amount of rainfall is required to remove salt from the plant 

 zone. Dune plants can tolerate moderate concentrations of salt and some 

 of them do not absorb salt through their leaves. All can tolerate some 

 salt in their root zone. In the upper beach and coastal dunes, the 

 lighter freshwater tends to float on top of the heavier seawater. In 

 humid climates percolating rainwater causes the development of lenses of 



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