196 CLIMAX FORMATIONS OF NORTH AMERICA. 



The center of the pond is covered with Nymphaea advena, surrounded by a 

 fringe of Sphagnum, in which grow Vacdnium, Eriophorum, and Drosera. 

 Beyond this occurs a zone of Chamaedaphne, though it is interrupted by 

 clumps of Betula, Nemopanthes, Larix, Rhododendron, and Vacdnium. The 

 next zone consists of Sphagnum, Acer rubrum, Betula, and Picea mariana, and 

 this is surrounded by Pinv,s strobus, Picea, Betula, Acer, Poprdus, Prunus, etc. 

 Harshberger (1909* : 373) has also made a further study of the structure and 

 general serai relations of the salt marshes and of the salt and fresh water ponds 

 of the New Jersey coast. 



Transeau (1909) has traced the succession in salt and fresh water about 

 Yarmouth, in Nova Scotia: 



The Laminaria formation of the submerged beach passes into the Fucus- 

 Ascophyllum formation of rocks, which is succeeded on the lower beach by the 

 Spartina glabra association. The latter also succeeds the Ulva formation of 

 mud flats, which in its turn has replaced the Zostera formation of muddy 

 shoals. The Spartina association passes into one of Spartina and Juncus, and 

 this into the Agrostis-Juncus association. The latter, as well as the Ammo- 

 phila-Atriplex formation, is succeeded by the Alnus-Myrica association, which 

 passes Anally into the Picea formation. Clearings and pastures also develop 

 the Alnus-Myrica formation and may then pass into forest as well. 



In fresh water the Potamogeton association yields to the Hippuris associa- 

 tion and this to one of Carex and Juncus. The latter may then develop into 

 the Juncus-Sphagnum association and pass through the Alnus-Myrica stage 

 into spruce forest, or it may be followed by the CaUimagrostis-Sphagnum asso- 

 ciation, and this by the Chamaedaphne-Rhodora association, either of which 

 may pass into the Alnus-Myrica stage. The Chamaedaphne-Rhodora stage 

 may be succeeded by a mixed forest of Larix and Picea, which may also pass 

 into the Picea formation. 



Chrysler (1910 : 171) has recognized the following serai zones in the fresh 

 water marshes of Maryland: 



(1) Potamogeton zone at 5 to 10 feet deep, with Brasenia, Utricularia, Lemna, 

 etc.; (2) Nymphaea zone, at 2 to 5 feet deep; (3) Pontederia zone at 1 to 2 

 feet, with Sagittaria; (4) Zizania on mud flats, with Bidens, Polygonum, and 

 Sagittaria; (5) Typha zone, often with Sdrpus, PeUandra, Orontium, and Iris; 

 (6) alder zone, of Cephalanthus and Alnus; (7) maple zone, Acer rubrum, Salix, 

 Fraxinus, etc. In the salt-marsh sere, Spartina stricta, S. polystachya, Typha, 

 and Sdrpus olneyi are pioneers in much the order named. With the last are 

 often associated Sdrpus, Cyperus, Lythrum, Pluchea, etc. The reed-grasses 

 are succeeded by Distichlis, and this by the Iva-Baccharis-Panicum associa- 

 tion, which in its turn gives way to shrubs and trees, Myrica, Rosa, Baccharis, 

 Juniperus, Pinus taeda, etc. 



. Shreve (1910) has described the marsh and dune vegetation of the Eastern 

 Shore of Maryland, and has sketched the successions in general: 



These are principally those taking place on the upland on account of changes 

 in physical condition due to erosion, and those taking place along the shore- 

 lines and due to the formation or exposure of new plant habitats. The flood- 

 plain forest is a temporary one, representing the transition from spring-swamp 

 to upland. The climax forest is probably one in which the pines predominate, 

 accompanied by oaks, gums, and maple. The feature of change in the shore- 

 line topography of the greatest effect upon vegetation is the filling-in of the 

 bays and the narrowing of estuaries. The deposition of silt in the marshes 



