82 ANIMAL LIFE AND SOCIAL GROWTH 



At times the lake winds may rip off the plant 

 cover in a weak or particularly exposed spot and 

 start what is graphically called a "blow-out." 

 These are more frequent in the fore-dune region 

 but may occur elsewhere in the dune complex. 

 When one is formed, its recapture covers many of 

 the stages and shows the majority of the processes 

 that have been outlined for the dune succession 

 as a whole until finally it too becomes completely 

 captured by the climax vegetation. 



Professor Cowles of Chicago, a pioneer student 

 of dune vegetation, found that plants appear to 

 be unable to stop the movement of a rapidly 

 shifting dune. Such a travelling dune is first 

 checked by a decrease in wind energy due to in- 

 creasing distance from the lake or to the growth 

 of barrier dunes which may form across the mouth 

 of a widening blow-out. Such barriers are formed 

 about pioneer vegetation just as in the growth of 

 the original fore-dunes. 



Throughout the whole process the animals and 

 plants form a series of units which exhibits the 

 loose co-operation characteristic of any community. 

 After the plants come into the succession on the 

 fore-dunes, they are the dominant force either 

 living or physical. The animals aid in preparing 

 the soil for their coming and in enriching it so 

 that still others can tolerate dune conditions. 



