284 



is a plant that grows best where there is an abundance of blowing 

 sand. In such situations it builds dunes to a bight of several meters. 

 In this region the Ainniophila dunes are in no case more than a meter 

 high. The dune has a very gradual slope, which is steeper on the 

 landward side. The plant spreads in lines and does not form clumps 

 as Calamovilfa does. Ammophila exceeds all other sand-binding 

 grasses in the ability to grow upwards with the accumulation of the 

 sand. At the same time the aggregation is so open that, in this re- 

 gion, it pennits the sand to be carried back into the lake almost as 

 fast as it is accumulated by the plant. This is the exact reverse of 

 conditions prevailing in the Calainoinlfa dunes, where the close bunch- 

 ing of the grass and the usually persistent dead leaves at the base of 

 the stem permit a more prominent heaping up of the sand. 



Ammophila dunes are pioneers of upper beach vegetation, but they 

 will not commence so near the drift beach as will the Calamovilfa. 

 On the other hand, Calamovilfa can capture the Ainniophila dunes 

 and replace the plants by which they were formed. 



The Ammophila dune association is so poorly developed in this 

 area that an adequate description of it is not possible from the data 

 at hand. An extended description is given in a paper by Cowles 

 (1899:179-181). The secondary species that occur have scarcely any- 

 thing to do with the growth of the dune. They merely represent 

 beach species whose seeds have lodged among the Ammophila stems. 

 Lathyrus maritimus, the beach pea, is the most abundant and best de- 

 veloped. Its procumbent stems trail in and out between the Am- 

 mophila stems for several decimeters. Like the other secondary 

 species, it occurs just over the crest, as viewed from the lake. The 

 main part of Figure 2, Plate XLVIII, is occupied by an Ammophila 

 dune. 



LIST 01^ THE SPKCIHS OF THE AMMOPHILA DUNE ASSOCIATION 



Dominant Species 

 Ammophila arcnaria 



Secondary Species 

 Calamovilfa longifolia Potcniilla anscvina 



Lathyrns maritimus 



Relic Species 

 Euphorbia polygonifolia Xanthium commune 



Invading Species 

 Calamovilfa longifolia Salix longifolia 



Prunus puniila Solidago graminifolia 



