293 



been constructed and fixed by planting willows upon it. For the most 

 part it is tenanted by species of willow, especially Salix longifolia and 

 S. glaiicophylla. The bushes form a fairly dense tangle about 1.4 me- 

 ters high, and mixed with them are individuals of wild rye (Bh'iiius 

 canadensis), horsemint (Monarda punctata), butter and eggs (IJn- 

 anaz'idgaris), wormwood (Artemisia caudata) and ya.rrow (Achillea 

 mill e folium). In a few places the dune is fronted by Junciis balticus 

 littoralis. Upon the west side of the dune the sodded ground extends 

 to its base. The south end is not sufficiently well protected, and con- 

 sequently the wind is undermining the willows to some extent. 



THE TRAVELING DUNE 



For reasons given before, this kind of a dune is not a feature 

 of the region; in fact there is but one present in the area. Its hight 

 above the lake-level is nine meters, and a few oaks have been partially 

 covered by it. 



The Upper Beach Associations 



THE ARTEMISIA- PANICUM ASSOCIATION 



This association, which is so wide-spread on Prescpie Isle and is 

 of general occurrence along the shores of Lake Michigan, is but 

 poorly represented in this region. A majority of the species men- 

 tioned by Cowles (1899:168 et seq.) occur upon it, but from 40 to 60 

 per cent, of the area is taken up by invading plants of the bunch- 

 grass association, which borders and is extending rapidly into it. 



Location and Physical Characteristics. — The area which stretches 

 back from the fringing dunes, is largely composed of sand whose 

 grains are about 0.5 mm. in diameter. The relative amount of sand 

 decreases in going away from the lake. At the same time the rela- 

 tive amount of gravel increases. The change is uniform, though 

 gradual. The Artemisia-Panicmn association occupies the sandier 

 parts of the upper beach, and thins out quite rapidly as the amount of 

 gravel increases. The reverse of this is true with respect to the bunch- 

 grass association. The sand is somewhat mobile, but not much so be- 

 cause of protection by the fringing dune and by the vegetation of the 

 bunch-grass association. Water is near tlie surface and is easily 

 available, but food materials dissolved in it are low in amount. The 

 aeration of the sand, aided by the relatively large spaces between the 

 grains and the sudden changes of temperature, is very thorough, 

 which leads to rapid eremacausis and consequent absence of humus. 



Ecological Characteristics. — Except for the absence of wave ac- 



