anaerobic conditions. Similar effects may occur with other elements or 

 compounds but these are not known to limit marsh creation. 



b. Exposure to Direct Sunlight . Tidal submergence greatly reduces the 

 amount of light which can reach inter tidal plants. Therefore, marsh plants 

 rely heavily upon uninterrupted light exposure for photosynthetic activity 

 during low water periods. Typically, the grasses, sedges, and rushes which 

 form the intertidal marsh community are exposed to direct sunlight, because 

 this zone lacks an overstory of either shrubs or trees. 



In general, woody vegetation is not found within the intertidal zone of 

 the coastal United States. The major exception to this is the occurrence of 

 red mangroves {Rhisophora wangle) in southern Florida. On the Atlantic and 

 gulf coasts, marsh-elder (Jm frutesaens) grows on the outer margin of salt 

 marshes. This plant grows closer to the marsh than any other woody species 

 and is appropriately referred to as the "high tide bush." On the Pacific 

 coast, frankenia {Fvankenia grandifolia) is the first shrubby species 

 encountered at the edge of the marshes. These and other shrubs form the 

 transition between the marsh and the maritime forest. 



Erosion patterns may alter the normal zonation of plant communities on the 

 shore. Progressive erosion may have obliterated the marsh and shrub transi- 

 tion zones leaving a mature forest overhanging an exposed bank. Such a 

 condition will preclude the establishment of emergent vegetation for erosion 

 control because of its impact on the availability of light. In peninsular 

 Florida, the introduced Australian Pine (Casuarina equisetifolia) often 

 induces erosion along steep shorelines by shading out the native intertidal 

 plants. If the area meets other criteria for erosion control with vegetation, 

 however, the area can be planted if the overstory is completely cleared above 

 the planting area and to a distance of at least 3 to 5 meters landward (Fig. 

 11). Continued control of overstoring species will be an essential part of 

 the maintenance of such sites. 



c. Shore Width Available for Planting . The width of the beach at an 

 elevation suitable for plant establishment will determine the relative 

 effectiveness of the erosion control planting. Waves are dampened as they 

 pass through stands of marsh vegetation. The amount of dampening that occurs 

 is directly related to the width of the marsh. From a survey of erosion 

 control plantings, Knutson, et al. (1981) concluded that a practical minimum 

 planting width is about 6.0 meters. If the potential planting area is not 

 sufficiently wide, the shore must be graded to extend the planting area. 

 Grading must be done far enough in advance of planting to allow for a consoli- 

 dation of the disturbed soil to take place. Otherwise, transplants may be 

 dislodged by the first minor storm before sufficient anchoring roots develop. 



Though there is some variation in the elevation (tidal) zones in which 

 marsh plants can be established, there are regional trends which are useful as 

 a general guide. On the Atlantic and gulf coasts marsh plants can be found 

 throughout much of the intertidal zone where the tidal amplitude is less than 

 about 2.0 meters. Where the tidal amplitude exceeds 2.0 meters, the lower 

 limit of invasion is more restricted. In areas of the north Atlantic where 

 the tidal amplitude may reach or exceed 3.0 meters, plants are restricted to 

 the upper one-half or less of the tidal zone. On the southern Pacific coast 

 (Fig. 1) marsh plants seldom extend below the elevation of mean tide even in 



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