.^f^^ 



FIG. 8-7 Sand sere at Ludington State 

 Park, Michigan, (a) the lower beach 

 (at right center) is washed by ordinary 

 waves; the middle beach (in center) 

 contains driftwood left by heavy 

 storm waves; the upper beach (at left) 

 has a sand dune well anchored by 

 grass and sand grape (light areas), 

 shrubs (dark areas), and Cottonwood 

 trees, (b) grass stage, showing 

 blowouts devoid of vegetation; a mixed 

 pine stage is shown in the distant 

 background (courtesy R.E. Rundus). 



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sere is as complete and as complex in the Lake Mich- 

 igan region as it would be anywhere. 



Habitat 



The sand dune habitat is characterized by ex- 

 treme fluctuations in physical conditions, generally 

 resembling those of a desert (Chapman ct al. 1926). 

 Temperatures, especially at the ground surface, are 

 very high during bright sunny days ; relative hu- 

 midity is very low. Evaporation from spherical at- 

 mometers is 2.5-3 times higher than in forest hab- 

 itats at the same time of day. At night the ground 

 surface temperature may be even lower than that of 



the air since there is little or no surface covering to 

 prevent rapid heat radiation. 



Correlated with the diurnal changes of tempera- 

 ture, relative humidity, and light, the kinds of animal 

 active on the sand during sunny days are quite dif- 

 ferent from those active on cloudy or rainy days and 

 at night. When the temperature of the sand nears 

 50°C, all insects leave the surface. Some climb 

 grasses to get off the ground, others enter their bur- 

 rows. Insects flying above the sand can select an 

 optimum temperature from widely different tempera- 

 tures merely by changing their elevation only a few 

 inches. They make hurried landings when entering 

 their ground burrows. The female velvet-ants are 

 usually among the last to retreat into their burrows 



106 Habitats, communities, succession 



