THE ECOLOGICAL RELATIONS OF THE VEGETATION 
ON THE SAND DUNES OF LAKE MICHIGAN. 
HENRY CHANDLER COWLES. 
[Concluded from p. 308.) 
D. THE ESTABLISHED DUNES. 
1. The basswood-maple series. 
IMwas shown in another place how the steep lee slopes of the 
slowly advancing dune-complex are first captured by social per- 
Be te like Ammophila and Asclepias. Then shrubs like 
_iimts Salix, and Prunus grow up and gradually drive out the 
herbs which grew there first, because they are ill-adapted to the 
“ade. With these shrubs there often develop many young trees 
| a basswood, Tilia Americana. As these trees grow rapidly, 
cob ns long before the thicket becomes a little forest, in which 
Ye dominant tree is the basswood. The basswood dune, more 
ei other type of established dune, is sui generis. It is to 
i along the entire coast between Dune Park and Glen 
the conditions that determine the development of the won- 
omg characteristic flora are very obscure. The gee 
Pe vt always very steep and relatively near the lake. Umilke 
* established dunes there is no approach to 4 vegetation 
ae he sandy soil is loose and bare and evidently piles 
iy and a5 The movement of the sand is due directly to ee 
tion hae indirectly to the wind. The only obvious : # 
‘Omp| ich favors the rich development of plants 1s the alm 
Protection from the wind. 
trees —- of the basswood dunes grow as thickly t 
Sts saad and much more thickly than in ant 0 
ther i 2684 where the basswood is the dominant 
a €gins to approach it in importance, althoug 
361 
ogether as 
ther dune 
tree ; no 
h Populus 
