186 



CLIMAX FORMATIONS OF NORTH AMERICA. 



are dominant, though Empetrum and the lichens are present. In very wet 

 areas, Vaccinium oxycoccus and Drosera rotundifolia are characteristic. Larix 

 americana grows farthest out into the bog, but Picea nigra is not far behind it. 

 In cross-section, the raised bogs show a layer of stumps at the bottom but 

 nowhere else. The peat is composed of pure Sphagnum, mixed with remains 

 of shrubs and sedges. The stump layer has arisen by the advance of the 

 Sphagnum, which cuts off the oxygen supply from the roots. The dead trunks 

 finally decay away, leaving the sound stumps in the antiseptic peat. The 

 homogeneous structure of the bogs makes it clear that they have not been 

 formed during alternations of climate such as Blytt has indicated for Norway. 



Rowlee (1897 : 690) has made a study of certain swamps in central New York, 

 and reached the following conclusions in regard to the succession in them: 



A complete swamp may be divided in accordance with the character of the 

 vegetation into three zones: (1) the lake in the center; (2) the moor comprising 

 the open area surrounding the lake, and generally grown over with Sphagnum; 

 (3) the wooded belt comprising the remainder of the swamp. In the maturing 

 of the swamp, these disappear in regular succession from (1) to (3). In many 

 places lakes have already been converted into moor, and in others, both lake 

 and moor have been succeeded by forest. 



Harshberger (1900 : 623) has described the plant communities of the New 

 Jersey strand, and has grouped them in an arrangement which suggests many 

 features of the succession: 



I. Sea-strand vegetation — Continued. 

 D. Marsh-dune formation. 



II. Salt-marsh vegetation. 



A. Tidal-flat formation. 



B. Saline-marsh formation. 



C. Converted saline-marsh formation. 



III. Bay-strand vegetation. 



A. Dmie formation. 



B. Bay-beach formation. 



IV. Bay-water vegetation, 

 (a) Buppia zone. 



(6) Nereid zone. 



I. Sea-strand vegetation. 



A. Beach formation, 

 (o) Snccxdeat zone: CakUe-Ammodenia, 



Salsola and AlripUx societies. 

 (6) Oenothera humifiLsa zone. 



B. Dime formation. 



(a) Ammophila zone. 



(b) Myrica zone. 



(c) Hudsonia zone: Rhus-Ampelopsia, 



dune-marsh and Baccharis-Rosa 

 societies. 



C. Thicket formation, 

 (a) Juniper zone. 

 (&) Mixed zone: Hudsonia, Scirpus, 



Typha, Osmunda, etc., societies. 



In a later paper (1902 : 642), attention is directed to the major features of 

 dune and marsh seres, and the successional zones are emphasized. 



Kearney (1900) has classified the plant communities of Ocracoke Island, on 

 the southern Atlantic coast of the United States, as follows. In the grouping 

 may be detected the general features of the hydrosere, and of the xerosere also: 



I. Sand strand vegetation. 



1. Treeless (open), 

 (o) Beach formation: Croton-Physalia 



association. 

 (6) Dime formation: UniolorYucca as- 

 sociation. 



2. Evergreen trees and shrubs, 

 (o) Tree formation: Qusrcus virginiana 



association. 

 (6) Thicket formation: Ilex vomitoria 

 association. 



II. Salt marsh vegetation. 



1. Creek-marsh (closed) formation, 

 (a) Spartina stricta association. 



(6) Juncus roemerianua association. 



2. Dune-marsh formation: LippiorMon- 



niera association. 



3. Tidal flat (open) formation: Sesuvium- 



Tisaa association. 



