10 REULAMATION OF CAPE COD SAND DUNES. 



The problem of controllinjy the drifting sand.s of the Cape has con- 

 cerned the municipal, State, and National authorities for two hundred 

 years, and the extensive planting of beach grass as a means of protec- 

 tion dates back for more than a centiuy. 



The ph3'siographic and botanical phases of the subject presented 

 are based upon the writer's personal observ^ations and collections. 

 The bibliography indicates the source of the historical features. Many 

 of the details were derived from an examination of the statutes and 

 town records, together with what covdd be deduced from local testi- 

 mony and personal observation. The details of the earl}' work of dune 

 control were obtained from the records on file in the War Department, 

 all the work of harbor protection on the part of the General Govern- 

 ment having been under the supervision of that Department. 



ecoiiogicax. relations of the vegetation. 



Ecological Factors. 



The ecological factors which are of the most importance in the con- 

 sideration of the sand-dune areas are light and heat, wind, soil, and 

 moisture. The low specific heat of the sand causes it to respond very 

 quickly to any change of temperature in the surrounding medium. 

 The sand becomes excessivel}' hot on the side of the dune exposed to 

 the direct ra^'s of the sun and for the same reason the cooling process 

 at night is (piite as marked. The extremes of temperature incident 

 to this condition are severe upon any form of vegetation and probabl}' 

 constitute the chief reason for the absence of many species which 

 might otherwise be present. The oceanic location of the area tends to 

 produce an equable climate. The tliermometer rarely registers tem- 

 peratures below 2'^ F. in winter or above 8.5" F. in summer, except 

 immediately upon the bare sand areas, where the conditions are much 

 less equable. 



The wind is an important factor for several reasons. Its effect upon 

 transpiration, especially when augmented by the high temperatures 

 incident to the heated layers of air at the surface of the sand, is very 

 marked. The distortions of the trees so often noticeable along the 

 coast are not present, as the rejuvenescence of extensive forested 

 dunes has destroyed the wood}' vegetation to beyond the limits of the 

 injurious effect of the un})roken salt-laden winds. The bombardment 

 by the sand which the wind hurls against the vegetation is especially 

 severe. The presence of sand as large as wheat grains (one-eighth to 

 one-sixth inch in diameter) in great quantities on the dunes testifies 

 to the force of the winter gales which swept it there from the beach 

 below. The force of this bombardment may be realized when walking 

 across a dune area during a strong wind or by examining the effect 

 of the sand blast upon the windward side of the exposed vegetation. 



