194 SEEDING AND PLANTING 



10. WANDERING DUNES. Dunes pass through a progressive 

 series of changes. Along the coast and large inland bodies of 

 water they originate near the beach and travel inland. These 

 wandering dunes have a more or less definite form and an abrupt 

 slope to the lee. They travel with the wind at a rate depending 

 upon its velocity and constancy. In the course of time as the 

 dune recedes from the beach a new one is formed near the shore 

 until a whole series finally appears as undulating sand ridges or 

 hills, often extending several miles inland. In their progress they 

 overwhelm all forms of vegetation, often burying forests that are 

 40 or more feet in height. So long as a dune is active it sup- 

 ports but little vegetation as the shifting sand prohibits its becom- 

 ing established. 1 Inland dunes are chiefly due to excessive grazing 

 or other factors which effect the removal of the vegetation. 2 They 

 often start as blowouts at the top of hills. The blowouts become 

 more and more enlarged through undermining the surrounding 

 vegetation and in time a wandering dune may result. The great 

 loss from active dunes is not only in their non-productive 

 character but also in their encroachment upon arable land, the 

 overwhelming of forests, cultivated fields, and other valuable 

 property. 



11. FIXED DUNES. As the wandering, or active, dunes move 

 from their place of origin, whether it be on the beach or on an in- 

 land sand hill, the action of the wind becomes less forcible. As a 

 result, the movement of the sand becomes more intermittent and 

 slower and vegetation has a better chance to become established. 

 During wet periods seeds germinate and gradually the active 

 dune is changed into a fixed dune. If the vegetation, although 

 scanty at first, is undisturbed, it becomes denser and in regions 

 of adequate precipitation it culminates in a forest. Thus, we find 

 many of our coast forests on fixed dunes. 



Any factor which adversely disturbs the vegetation may re- 

 convert a fixed dune into a wandering one. Thus, large areas, 

 both in this country and abroad, which were formerly fixed dunes 

 covered with forests have, with their removal, become wandering 

 dunes. 



1 Cockayne, L.: Report on the dune-areas of New Zealand. (Dept. of 

 Lands. Wellington, 1911.) 



2 Bates, C. G. and Pierce, R. G. : Forestation of the sand hills of Nebraska 

 and Kansas. (U. S. Forest Service, Bui. 121. 1913.) 



