360 Proceedings Portland Society Natural History 



occupied the crests. In the case of most cliffs the possible 

 lower limit of tree growth as determined by wave action dur- 

 ing the winter storms is located at the very edge and often 

 the forest has been able to colonize the entire available sur- 

 face. In such locations there is an abrupt transition be- 

 tween the coniferous woods and the bare rock face with no 

 intermediate stages, a condition illustrated in Figure 19. 

 More often, however, even though the trees extend to the 

 edge of the bluffs, there is a narrow fringe of Empetrum 

 present and overhanging the cliffs. Again, as in the condi- 

 tion described above, there may be a definite area at the 

 summit where trees have failed to develop and the ground is 

 occupied by the prostrate shrub association-type. 



When trees are present on these sea cliffs they frequently 

 show the effects of the constant exposure to which they are 

 subjected by their gnarled or stunted growth, or in some 

 other manner. On the Eastern Ear of Isle au Haut where 

 the forest is exposed to an almost incessant buffeting of 

 wind and spray, the trees back from the crest, in this case 

 the white spruce, are so dense that, according to Norton 

 (25), "a person of two hundred pounds weight may walk 

 from the ground to the summit on the ends of the densely 

 matted and tangled branches." 



Association-types of headlands 



Where conditions are very extreme the treeless zone ex- 

 tends back a considerable distance from the crest of the 

 bluffs, and a barren headland results. The lower limit of 

 possible tree growth in such an area may still be at the edge 

 of the cliffs or even nearer the water, but the presence of 

 various retarding influences, such as the nature of the rock 

 surface, the steepness of the slope, and the degree of ex- 

 posure, commonly prevent the occupation of the area by 

 forests. Figure 18 pictures such a headland in which the 

 forested portion is restricted and the trees show the effects 

 of exposure. 



