304 



though this region is no longer a breeding place for gulls. The sand- 

 plain is very flat, and slopes down away from the lake rather than to- 

 wards it. Ordinarily the sand is fixed; but when storm waves are 

 able to effect entrance, the sand is released and is usually blown into 

 the lake. 



Hcologlcal Characteristics. — A comparatively thin growth of grass 

 sufficiently dense to prevent blowing but not sufficiently dense to ob- 

 scure the yellowish color of the sand, is the prevailing feature of this 

 association. Secondary species occur here and there but are nowhere 

 of much importance, since they occur as scattered individuals among 

 the grass plants, which form about 90 per cent, of the area. Near the 

 lake the grass plants are separated two to three centimeters (see 

 foreground, Fig. i, PI. XLVI). On the ridges nearer the western 

 boundary, however, the grass plants grow much closer together and 

 form a true sod, which is usually effective in preventing further suc- 

 cession. 



The Association. — The grass, Poa compressa, is the dominant spe- 

 cies and thoroughly characterizes the association. The secondary 

 species are, for the most part, merely sand plants which happen to be- 

 come established. Some of them are relics of the Qiiercus velutina 

 association in places where oaks have been removed, others are nor- 

 mal beach-plants, and several are weeds that grow readily in sandy 

 ground. Ecesis (establishment) is not difficult for the weeds, since 

 the ground is so open. A few species are indicative of successions. 

 Near the lake the presence of small plants of Juniper us horisontalis and 

 /. coniniunis deprcssa look toward a heath, but in some other places 

 the dense growth of this grass has been responsible for the dying out 

 of the junipers. On the ridges farther inland the occasional pres- 

 ence of seedling trees indicates the approaching development of a 

 forest. 



LIST 0^ THE SPECIES OE THE POA COMPRESSA ASSOCIATION 



Dominant Species 

 Poa compressa 



The most important secondary species near the lake shore 

 Monarda punctata Cenchriis caroUnianns 



Sporobo his cryp tandriis 



Other secondary species near the lake shore 

 Verbena hastata Achillea inillefoliuni 



Brigeron canadensis Anaphalis niargaritacea 



