THE ENVIRONMENT 



329 



vail along the ocean in coastal strands and salt 

 marshes and inland around salt lakes or saline basins. 



Inland saline habitats usually are limited to arid 

 regions where rock weathering releases salts that are 

 transported by water to collecting basins. In these 

 lakes the water may or may not be seasonal, but 

 whether they are permanent or temporary, the salin- 

 ity of the waters is usually high. In salt flats there 

 also may be a seasonal fluctuation in topsoil salts. 

 The salts may leach downward during a wet period 

 and rise again with evaporating water during the dry 

 season; with either alternative, the vegetation is lim- 

 ited to salt plants. 



Salt plants possess properties that enable them to 

 exist in situations that are impossible for most plants, 

 places with abundant water but too much salt. These 

 environments are called physiologically dry because 

 water is present, but not in a form that is usable by 

 most plants. Yet salt plants survive by one or both of 

 two general methods. The first method involves the 

 actual intake of salt with the water and special glands 

 that excrete excess salt from cell fluids. The other 

 method is a complex chemical process. 



Another and little understood specialization of salt 

 plants is the succulent vegetative form. Most of these 

 salt plants, whether they be coastal or inland (in fact, 

 both areas often share the same species), have soft, 

 thick tissues and organs that contain an abundance of 

 water — in other words, a succulent structure. Al- 

 though succulence does appear to be an adaptation to 

 store water for use during the more adverse periods, 

 this does not really explain why strictly maritime salt 

 plants should be succulents. The latter are capable 

 of extracting the water they need from high tidal 

 ocean waters and would seem to require no water 

 storage. 



Salt plants tend to be shallow rooted. This is an 

 advantage in that fresh water is made available when 

 rain leaches salts below the roots. Shallow rooting 

 also aids in aeration, because saline subsoils usually 

 are waterlogged. Although salt plants are shallow 

 rooted, they often are extensively rooted. This is 

 especially the case in those species inhabiting wind- 

 swept coastal strands where plant existence is some- 

 what dependent upon individual plants' "holding" 

 the loose sands. 



There often is some confusion between alkaline and 

 saline areas, because the two habitats share a basic 

 pH and the same or similar salt plants. However, 

 saline sites are rich in free salts and usually have a 



pH below 8.5, whereas alkaline areas have few free 

 salts and a pH often above 8.5. In spite of these eco- 

 logical differences, the habitats are similar in vegeta- 

 tion because only salt plants are uninjured by either 

 salt or alkali. 



SOIL ANIMALS 



The size of adult animals within the soil allows soil 

 fauna to be summarized in four main groups. Each of 

 these groups is distributed throughout the horizons 

 of any particular soil and the organic layer above the 

 soil (see Figure 5.1, p. 76). Therefore, fallen trees, 

 isolated logs, and any plant or animal remains upon 

 the soil are considered part of the medium of the 

 soil animals. 



Although soil animals vary a great deal, mostly in 

 relation to the characteristics of each of the organic 

 and soil horizons, the adult animals can be defined 

 as follows: 



largest animals, including small mammals, reptiles, 

 amphibians, arthropods (millipedes, centipedes, 

 and large spiders, scorpions, and insects), large 

 earthworms, and large snails and slugs. 



fairly large animals, including arthropods (garden centi- 

 pedes, most millipedes and centipedes, ticks, most 

 spiders and scorpions, harvestmen, sun spiders, 

 and most large insects) and moUusks (most snails 

 and slugs). 



smallest macroscopic animals, typified by a vast array of 

 small arthropods (pauropods, garden centipedes, 

 mites, whip scorpions, larval insects, and the small- 

 est spiders and insects) and many kinds of round- 

 worms. 



microscopic animals and protozoans, including arthropods 

 (water bears), cavity worms (roundworms and 

 wheel animalcules), the smallest free-living flat- 

 worms, and a great variety and number of proto- 

 zoans. 



The occurrence of individual species of animals 

 appears to be less restricted by soil conditions than is 

 the occurrence of plants. However, soil texture dis- 

 plays clear associations with certain animals. For 

 example, legless lizards, horned lizards, and kangaroo 

 rats may be geographically restricted more by soil 

 texture than by any other ecological factor. Each 

 group generally is confined to sandy or loamy soil. 

 In addition, the amount of organic matter, moisture, 



