828 JOURNAL OF FORESTRY 



Hawley and Hawes'^ include the island in the northern spruce re- 

 gion ; in reality it is at the edge of this region and contains several 

 features of the white-pine region. This location in the tension zone be- 

 tween two forest regions offers unusual opportunities for studying suc- 

 cession in forest types and for determining whether or not the north- 

 ward migration of plants which followed the retreat of the ice-sheet is 

 still going on.^ Fortunately the setting aside of 5,000 acres of the island 

 as a national monument will permit the making of long-time studies cov- 

 ering these and other matters of interest to foresters and ecologists. 



The topography is of the most varied, from a rolling plain to almost 

 sheer precipices nearly a thousand feet in height. This offers, as may 

 readily be imagined, a wealth of habitats. 



Climate 



The climate is marine, the ocean tending to keep the temperature 

 uniform but cold, for the island lies beyond the influence of the Gulf 

 Stream. Parts of the island are, however^ so shut off from the ocean 

 winds as to have a climate almost continental and are subject to con- 

 siderable fluctuations in temperature. The large areas of granite rock 

 (see geology below) take up and radiate enormous quantities of heat, 

 causing temperature fluctuations which, particularly in places protected 

 from the ocean winds, must have a distinct bearing on the vegetation. 

 The mean annual temperature at Bar Harbor is 44° F., running from 

 a monthly mean of 21° for January to 65.5° for July- 



The average annual precipitation is 48.3 inches, of which only one- 

 third, or 16. 1 inches, comes in the growing season (May to September, 

 inclusive). Although this amount should be more than ample, there 

 are periods during the summer when lack of moisture is an important 

 factor in coniferous reproduction, especially on rocky sites. 



Geology 



A brief glimpse of the geology^ of the island will aid in understand- 



' Hawley, R. C, and Hawes, A. F. : "Forestry in New England." New York, 1912. 



^Griggs, R. F. : "Observations on the behavior of some species at the edges of 

 their ranges." Bull. Torrey Botanical Club 41 : 25-49, I9I4- See esoeciall-"^p. a?. 

 For indications of this phenomenon on Mt. Desert Island, see under "The Vegeta- 

 tion, General," p. 830. 



Gleason, H. A. : "The vegetation of the inland sand deposits of Illinois." 

 Bull, of the 111. State Lab. of Nat. Hist., Vol. 9, article 3, pp. 23-174, 1910. Es- 

 pecially pp. 44 and 45. 



'Davis, Wm. M. : "An outline of the geology of Mt. Desert." In Rand and 

 Redfields "Flora of Mt. Desert Island, Maine," pp. 44-71, Cambridge, Mass., 1894. 



Shaler, N. S. : "The geology of the island of Mt. Desert. Maine." Report 

 Secretary of Interior to ist Session of 50th Congress, Vol. 3, part 2, pp. 987- 

 1063, 1889. 



