Although large areas of marsh grow on organic substrates, these 

 are generally the least desirable soils for planting. Most of the 

 marsh situated on organic substrates is the result of peat formation 

 in place under the growing marsh. The marsh was probably established 

 before peat formation began. Organic soils and particularly fibrous 

 peats are very difficult materials, both physically and chemically, 

 in which to plant marsh species. The mechanics of opening and partic- 

 ularly closing planting holes or furrows are difficult. Nutrient 

 deficiencies result in slow growth and poor survival. Direct seeding 

 of such sites is next to impossible since the seedbeds do not retain 

 seed long enough to allow germination and establishment. 



2, Salinity . 



Salinity is the one common factor that affects all salt marsh 

 plants. These plants must have some salt tolerance, a prime require- 

 ment in this habitat. Some of the more tolerant species have the 

 capacity to excrete salt through special structures (salt glands) in 

 their leaves. A number of them possess another mechanism in their 

 roots for screening toxic ions and slowing absorbtion (Waisel , 1972) . 



Plants of the .regularly flooded, low marshes, such as smooth 

 cordgrass. Pacific cordgrass, and the mangroves, are well equipped to 

 live and grow in salinities up to 35 parts per thousand (sea strength) 

 However, these plants are usually quicker to establish and more pro- 

 ductive in salinities below sea strength. Seeds and young seedlings 

 are usually more sensitive to salt concentration than are established 

 plants. 



Relatively little work has been done on salinity regimes of marsh 

 soils and their effect on plants under field conditions. Soil salin- 

 ity is not easy to investigate because of the high variability, in 

 time and space, of salt concentrations. The concentration of salt 

 required to eliminate a particular species from a site need not occur 

 often or persist for more than a few hours or days. Consequently, 

 these events may elude fairly intensive sampling. 



Toxic concentrations usually do not develop in sandy marsh soils 

 within the regularly flooded zone. The free water salinity in such 

 soils tends to remain close to that of the surrounding water. This 

 may not always be true of fine-textured soils in which salt may accu- 

 mulate through ion exclusion by roots (Smart and Barko, 1978), although 

 it does not appear to be a common occurrence in natural marshes. Salt 

 accumulation in the fine-textured marsh soils is probably held to a 

 minimum by the drainage normally provided by root channels and animal 

 burrows . 



27 



