Nichols: The vegetation of Connecticut 263 



Fraxinus americana Fraximis pemisylvanica 



Fraxinus nigra 



The Temporary Nature of Flood Plain Forests. — It has been 

 shown in the preceding pages that during the development of a 

 flood plain the vegetation becomes less hydrophytic and more 

 mesophytic, culminating in the formation of a mesophytic forest. 

 Such a forest is to be regarded as the climax association of flood 

 plains. But it can easily be seen that, owing to the activity of 

 the river, this forest may be relatively short lived; in other words, 

 it may represent only a temporary climax. For as the river 

 meanders about on its flood plain in serpentine curves, it is con- 

 stantly wearing away its banks on the outer, concave side of each 

 bend, while at the same time deposition is usually taking place 

 on the opposite, convex shores. In this way "a river may swing 

 quite across its flood plain, destroying all that it has built, including 

 the mesophytic forest."* Changes of this sort take place with 

 appreciable speed and may be observed along almost any 

 depositing stream. 



Ox-how Ponds. — In this connection should also be mentioned 

 the crescent-shaped curves, or ox-bows, which are a characteristic 

 feature of old-age streams. Frequently the meandering river 

 shifts its course, abandoning a loop-like channel for a more direct 

 route. The loop then becomes an ox-bow pond (Fig. i, D), and 

 as such its vegetation can best be treated wath that of ponds and 

 swamps, t 



TJie Subsequent History of Flood Plains. — One other phase of 

 river activity may be briefly sketched. It has already been shown 

 that while deposition is the main feature of old-age streams, 

 erosion is not wholly absent. In the course of time, for various 

 causes, downward cutting may be renewed, the flood plains become 

 terraces, and new flood plains may ultimately be formed at lower 

 levels. The resultant topography is well illustrated along the 

 Connecticut and others of the larger streams. The low flood 

 plains of today are comparatively recent in origin. The more 

 ancient flood plains are represented by sandy terraces, of which 



* Cowles, H. C, 1901, op. cit., p. 107. 



t See Bull. Torrey Club 42: 171. 1915. Fig. i of this paper pictures a 

 typical ox-bow pond. 



