EDAPHIC OR SOIL FACTORS: CHEMICAL 



197 



content of the soil solution to be the most decisive factor in the dis- 

 tribution of plant species and communities on low-level coasts. Belt 

 transects by English investigators clearly demonstrate this principle. 



Similar belt formations are also to be observed near the lagoons of 

 the ]\Iediterranean Sea, where, however, the decrease of sodium con- 

 tent inland runs parallel to and simultaneous with declining moisture of 

 the soil (Fig. 105). 



Where wet saline areas are in immediate contact with dry saline 

 soils, a very different zonation occurs. This may be seen around the 

 shotts of high Algerian plateaus, 

 whore the following zonation 

 obtains: 



1. A salt-water belt of J uncus sub- 

 ulatus and Scirpus marilimus. 



2. A little above water level a belt of 

 Salicornia fruticans. 



3. Small elevated hummocks formed 

 by a belt of Halocnemum strobilacettm. 



4. A gypsum border of the shott 

 with a belt of Frankenia thymifolia and 

 Lepidium subulatum. 



Fig. 

 Lagoon 



105. — Belts of vegetation of the 

 of Palavas (southern France) 

 according to decreasing NaCl content 

 of the soil at a depth of 10 cm. A, 

 Open water; B, Salicornietum herbaceae, 

 pH 7.3, Chlorides 1.136 per cent; C. 

 Salicornietum fruticosae, pH 7.2, chlo- 

 rides 0.948 per cent; D, Atriplex portu- 

 lacoides, pH 7.4, distinct traces of 

 chlorides; E, Atriplex and Agropyrum 

 elongatum, pH 7.4; no traces of chlorides. 



The maximum concentration of 

 salt is found in the Halocnemum 

 belt. 



The salt plants of the lagoons 

 germinate in the winter and spring. 

 Their major development occurs in the period following the heaviest 

 precipitation and therefore with the smallest salt concentration. In 

 the late summer, when under the influence of the burning rays of the 

 sun, the capillary rise of the soil salts has reached its maximum, the 

 annuals are already withered, and shrubs have reached their fruiting 

 stages. Their root hold is generally very weak and superficial, thus 

 avoiding the salt concentration of the soil at depths of 25 to 50 cm. 

 Tall bushes, as Salicornia macrostachya, root only to a depth of 10 to 

 15 cm., and it is easy to remove the entire upper layer of the soil with 

 the roots. 



The following may be cited as extremely perhaloid-anastatic asso- 

 ciations of the sodium chloride soils of southern Europe: the Suaeda 

 maritima-Kochia hirsuta association of the small lagoons in coastal 

 dunes; Salicornietum radicantis (resists the longest flooding); Sali- 

 cornietum fruticosae, which, with Atriplex portulacoides, covers 

 many square miles (Fig. 106); and the Salicornietum macrostachyae 



