The Plant Societies of Monterey Peninsula 15 7 



beyond Pescadero is not known. It is very evidently less well 

 adapted to establish itself in localities subject to the action of 

 heavy winds than is its associate the Monterey cypress, which 

 grows upon uninviting granite cliffs and in the very teeth of the 

 wind. 



Between the pine forest and the sea the wind has for a long 

 time been piling up a series of sand dunes that serve the forest 

 as a windbreak, and under the protection thus afforded a certain 

 percentage of each year's seedlings escape destruction. 



The innermost dunes have encroached upon the outer limits 

 of the forest to such an extent as to bring about the destruction 

 of some large trees; and it is not improbable that as the destruc- 

 tion of forest vegetation continues the inner limits of the dunes 

 may in the course of generations be found much farther inland 

 than at present. 



Cowles, in his studies of the Lake Michigan sand dunes, has 

 pointed out the interesting fact that where the growth of a dune 

 is slow, pines and certain other trees are capable of maintaining 

 themselves for many years, though the gradual accumulation of 

 sand renders the life of the afflicted tree much shorter than it 

 might otherwise be under perfectly normal conditions of growth. 

 This fact is likewise true of the Monterey pine, as may be seen 

 by a comparison of figures three and four. Figure three is a 

 good illustration of the advance of dune formation through a 

 part of the forest. Here the accumulation is slow and the trees, 

 though somewhat impaired in vigor and development, are man- 

 aging to hold their own very much more satisfactorily than are 

 the trees shown in figure four where the growth of the dune is 

 markedly much more rapid. The living pines seen at the left 

 stand in a pocket of some depth, but this, too, is gradually filling 

 up, and the trees occupying it are certainly doomed to an ulti- 

 mate burial. 



It would indeed prove interesting to carry on an extended 

 Study of this problem of the relation of the sand dunes to the 

 forest; for without doubt trees existing under such conditions, 

 exposed as thev are to the action of severe winds and advancing 

 sand, must undergo some interesting physiological and structural 

 changes. 



