WIND-BLOWN SAND 



47 



movement begins. As pointed out above many plants are able to 

 sustain themselves in competition with a growing dune, but they 

 are helpless when a dune is blown away from around them. The 

 roots which were sent out from the trunk are exposed to the air 

 and the tree perishes. Examples, as shown in Figure 4, are com- 

 mon in a dune region where trees grow. Plant life, however, es- 

 pecially the sand reed, resists dune-destruction and remnants of 

 the dune may be found held together by the closely woven root 

 system of the plant (Fig. 5). 



Aside from dune-building and dune-destroying wind-blown 

 sand acts like a ''sand-blast" and frequently cuts the bark from 

 the windward side of tender branches and shrubs; erodes away 

 the softer parts of tree trunks; polishes rocks and pebbles, or 

 the bones of some unfortunate animal that has perished in the 

 sand; or carves the exposed rock ledges into many fantastic 

 forms. 



Plant Life. 



The plant life of a dune area will vary with the prevailing 

 climate hence one description will fit only the specific case. If 

 the south end of Lake Michigan be taken as an illustration the 

 principal floral units are as follows : The beach is without vegeta- 

 tion, as the sand is alternately dry and wet and is affected severe- 



FiGURE 5. — Sand reed and other vegetation actin< 

 binders and preventing dune migration. (Fuller.) 



as sand- 



