FORESTS OF SAN JUAN ISLAND 



181 



trees on the three elevations referred to seems to be no greater 

 than in other places where the forest flourishes in spite of the 

 influence of wind on the tree tops. On Spieden Island occasional 

 trees are found on the southern slope and even these are practi- 

 cally free from wind effects. Many of the trees on the southern 

 slope of Spieden Island are Quercus garryana, a very few are 

 Pseudotsuga taxifolia. A good many specimens of Quercus 

 garryana are found on the summit of the ridge, while only occa- 

 sional ones are found in the forest on the northern slope, and 

 these only near the summit. 



Fig. 4 The south slope of Spieden Island (photograph by Ethel M. Bar- 

 dell). 



The conditions here of a transition from a yellow clay soil 

 producing a fir forest to a gravelly soil producing pract cally no 

 trees is strikingly similar to the conditions found near Tacoma, 

 Washington, where the forest borders the open gravelly prairie. 

 The fringe of oaks between the forested area and the open prairie 

 occurs in both cases. 



It is seen, then, that of the four conspicuous cases of barren 

 southern slopes and forested northern slopes above referred to. 



THE PL.txT WORLD, VOL. 16, NO. fl. June, 1913 



