Decreasing NaCl content 



202 PLANT SOCIOLOGY 



B. Keller (1923, p. 38) recognizes three associations of annuals in the 

 desert steppes near Sarepta arranged in accordance with decreasing salt 

 and moisture content of the soil: the Salicornia herhacea, Suaeda 

 maritima, and Petrosimonia crassifolia associations and two half-shrub 

 associations: the Halocnemum strohilaceum and the Atriplex verruci- 

 ferum association. The two first occur, with approximately the same 

 composition, on NaCl soils of European coasts. 



The solontschak associations of the arid steppes of Turkestan are 

 more pecuHar. According to Sprygin and Popow nine communities 

 (or associations) are distinguished with decreasing moisture and salt 

 content of the soil. 



Community 



Salicornia herhacea 

 Halocnemum strohilaceum 

 Halostachys caspica 

 Kalidium caspicum 

 Suaeda arcuata 

 Salsola crassa 

 S. lanala 



Artemisia viaritima 

 Anabasis salsa 



Halocnemum strohilaceum forms an important constituent of the 

 halophytic vegetation on the shore of the north African shotts, while 

 the Anabasis salsa association of Central Asia is represented upon the 

 sulphate soils of northern Africa by the A. aphylla and the A. articulata 

 associations of the arid desert. These deserts represent very extreme 

 xerohalophytic habitats. Stocker (1930) has found the concentration 

 of the soil solution in the upper layer of soil (1 to 10 cm.) of a wadi in 

 the Lybian desert to be 51 per cent, the osmotic concentration being 

 336 atmospheres. At a depth of 25 cm. the salt content of the soil 

 solution is 7.8 per cent, with an osmotic value of 39 atmospheres. Still 

 the spot possesses vegetation ! 



Kearney (1914, 1918) is conspicuous among the American investi- 

 gators who have examined the vegetation of the sulphate soils of that 

 continent. Upon soils with a predominance of chlorides but also with 

 considerable quantities of sulphates an association of the desert salt 

 bush, Atriplex polycarpa, prevails on moderately inclined slopes of 

 southern Arizona and in the dry regions of California. These receive 

 occasional light rains. Large areas are covered with the pickleweed, 

 Allenrolfea occidentalis, which can endure salt concentrations that 

 admit only a few grasses and shrubs but no annuals. In the region of 

 the Gila river on sulphate soil the com.posite Pluchea sericea (arrow 

 weed) forms impenetrable thickets as tall as a man. 



