THE ENVIRONMENT 



321 



treated as a saturated soil stage, because it is found 

 in both saturated and moister soils next to bodies of 

 water. 



Fringing woodland stage: This moist soil community 

 takes a variety of forms depending on local climate 

 and topography. If the stage has restricted available 

 water there may be only a few species of shrubs 

 and/or trees present; these plants are in the form of a 

 woodland. However, if available moisture is high the 

 stage may assume the appearance of a dense forest. 

 In a lush situation, the following species of plants may 

 be found; a tree layer or layers composed of maple 

 (Acer), elm {Ulmus), ash {Fraximis), sycamore {Plala- 

 nus), and cottonwood (Populus); and a shrub layer 

 composed of alder (Alnus), willow {Salix), and dog- 

 wood {Cornus). In addition, there may be well-de- 

 veloped herb, moss, epiphytic, saprophytic, and 

 parasitic life. 



Another tree often found with the above group is 

 oak {Quercus). In many cases the oak merely con- 

 tributes to a woodland-to-forest situation in con- 

 junction with the other trees and the shrubs. How- 

 ever, in some cases the entry of oaks constitutes a 

 more advanced stage in succession. Even though this 

 is the case, the other species normally remain a part 

 of the habitat. 



Dystrophic Lakes. "Bad-producing" lakes typically 

 contain acid-producing vegetation, usually sphagnum 

 moss (Sphagnum) but sometimes other vegetation, e.g., 

 sedges (Carex). The stages are only vaguely similar 

 to those found in an eutrophic lake; the lake usually 

 can be diagnosed on the basis of moss or acidity of the 

 waters (Figure 17.14). 



Open Water Stage. Very few organisms are present. 

 The stage often has only a few species when ad- 

 jacent stages are composed of acid-producing plants. 



Moss Stage. The innermost stage may consist of 

 floating moss; however, there may be a series of stages 

 comparable to the submerged-to-emergent stages as 

 they are found in oligotrophic lakes. These oligo- 

 trophic-like stages would then supplant the moss 

 stage; however, the subsequent communities would 

 be the next two listed. 



Bog Stage. This community is similar to the sedge 

 meadow stage of oligotrophic lakes in that the vege- 

 tation forms a dense, sodlike mat. However, the 

 species compositions of the two are very different, and 

 the bog stage usually extends much farther out over 

 the water. 



Shrub Stage. The dystrophic shrub community 



open 



Figure 17.14 Developmental stages in a dystrophic lake. 



normally consists of a unique assemblage of vegeta- 

 tion. In sphagnum bogs, cranberries [I'accimum) 

 and Labrador tea {Ledum) often are quite common. 

 However, sphagnum bogs and their allied vegetation 

 are uncommon in subtropical and more arid areas. 

 In these latter areas, dystrophic lakes typically are 

 not as acid and the shrub stage vegetation tends to 

 consist of the hardier, acid-resistant, semiaquatic 

 plants. 



Saturated and Moist Soil Stages. These communi- 

 ties are much the same as those found around eutro- 

 phic lakes. 



Volcanic Lai(es. These bodies of water are diag- 

 nosed on the basis of their stages, substrate, or pH 

 (acid, neutral, or alkaline). Ecologically they can be 

 similar to oligotrophic, eutrophic, or dystrophic 

 lakes. For practical purposes, it probably is best to 

 consider them as such. 



Altiali and Saline Lakes. Although these lakes are 

 chemically different, they present a similar ecological 

 situation. One can determine whether a particular 

 lake is saline or alkaline; however, further treatment 

 of subunits is very similar. 



Functionally, these lakes are dry habitats, very 

 little water being available to plants not adapted 

 to the habitat. Three developmental stages usually 

 are recognized (Figure 17.15). 



Open Water Stage. Surprisingly, perhaps, many 

 creatures often are in the open water, as well as the 

 margins, of these lakes. The species are mostly 

 arthropods but are different from those in the open 

 water stage of eutrophic lakes. Also, some neus- 

 ton, plankton, nekton, and benthos normally are 

 present. 



