CHAPTER SIX 



KENNETH H. DUNTON 



Marine Science Institute 

 University of Texas, Austin 



HEATHER D. ALEXANDER-MAHALA 



Marine Science Institute 

 University of Texas, Austin 



Vegetation 

 Communities 



"Ye marshes, how candid and simple and 

 nothing withholding and free 



Ye publish yourselves to the sky and offer 

 yourselves to the sea! 



Tolerant plains, that suffer the sea and the 

 rains and the sun. . ." 



♦ Sidney Lanier (1878) 



INTRODUCTION 



A primary factor affecting the growth and distribution 

 of coastal halophytes (salt-tolerant plants) is soil 

 salinity (Chapman 1974; Ungar 1974; Riehl and Ungar 

 1982; Clewell 1997). Halophytes are able to tolerate 

 relatively high concentration of sodium (Na*) and 

 chlorine (CI ) because of physiological mechanisms 

 allowing them to exclude, compartmentalize or extrude 

 salts (Badger and Ungar 1990). Several halophytes, 

 including Salkomia sp. and Suaeda sp., even exhibit 

 stimulated growth at some salinity levels (Ungar 1991). 

 However, there is for each species a salimty 

 concentration at which the effectiveness of these 

 mechanisms is compromised, and growth and 

 reproduction are limited (Adam 1990). 



High soil salinity negatively impacts the reproductive 

 ability of halophytes by decreasing seed viability. 

 Hypersalinity can result in a reduction in the number 

 of seeds germinating, a delay in the initiation of 

 germination and an increase in the number of seeds 

 remaining dormant (Ungar 1962; Chapman 1974; 

 PhilipupiUai and Ungar 1984; Ungar 1995). Each of 

 these consequences ultimately leads to decreases in 

 plant cover and increases in bare soils, which can 

 persist indefinitely until fireshwater inimdation (via 

 either precipitation or flooding) occurs diluting the 

 soils, alleviating the salinity stress and breaking the 

 osmotically induced seed dormancy (Ungar 1962; 

 Ungar 1978; Ungar 1995). Once germination takes 

 place, successful seedling growth is also salimty 

 mediated. The period of seedlmg development is 

 probably the most sensitive time during the life cycle 

 of a halophyte because the seedlings develop close to 



Chapter Six ♦ 6-1 



