ECOLOGY OF ISLE ROYALE. 139 



The Yellow-legs, Spotted Sandpiper, Bittem and Marsh Hawk range 

 far to the north, even to the Barren Grounds, and thus suggest chances, 

 as in the case of the aquatic association, of an early arrival and suc- 

 cession upon the island. 



With the growth of the island, there has been a corresponding ex- 

 tension of the outer and inner shore habits, although the encroaching 

 vegetation has had a marked tendency to restrict the area of the inland 

 habitat. The dominant environmental influences in this habitat appear 

 to be, 1, the physical character of the shore and beaches; 2, the dynamic 

 forces of the water bodies and streams; 3, the encroachment of the 

 vegetation; 4, the downward migration of the shore; and 5, the habits 

 and structure of the birds. 



As a general rule, we may say that the beach of the outer lake 

 tends to be succeeded by either the bog or upland associations, and 

 .those inland by the bog associaition. 



c. Bog-forest Association- and Habitat. 



As just stated the outer coast or an inland one may develop into 

 a marsh or bog habitat or association. In the bog, the Tamarack, 

 Black Spruce and Arbor "Vita? are the pioneer trees in transforming 

 the open marsh into a forested one; while upon the outer shore the 

 alders and aspens tend to precede the conifers as a general rule. 

 Prom the bog forest the transition to the Balsam-White Spruce forest 

 may be perfectly continuous, and thus there will be a series character- 

 ized by the dominant conifers. In places Arbor Vitse may form the 

 dominant swamp forest, but this is only a variation in the conifer domi- 

 nance. With improved drainage or the accumulation of vegetable 

 debris, these habitats become converted . into the Balsam-spruce climax 

 forest and hence the environmental dynamic tendency. 



As the forest encroaches iipon the open bogs the Tamarack, Black 

 Spruce, Arbor Vitse, Cassandra, Labrador Tea and alders are accom- 

 panied, by birds characteristic of this early stage; such as the Eed-- 

 breasted Nuthatch, Yellow-bellied Flycatcher, Golden-crowned Kinglet, 

 Cedar Waxwing, Chickadee, Canada Jay, White-winged Crossbill. 

 Where alders abound the conditions are favorable for the Redstart and 

 the White-throated Sparrow. But later, as the bog conifer forest 

 becomes continuous and dominant, the Waxwing, Redstart and White- 

 throated Sparrows diminish in numbers and finally disappear. Still 

 later, as the swamp becomes eliminated with the development of the 

 climax forest, the Yellow-bellied Flycatcher will also become excluded. 



This is perhaps the simplest succession from the water to the climax 

 forest, via the bog forest. This series is very perfectly preserved in 

 all stages and has an extensive range. The number of species in the 

 association is rather large when compared with the preceding asso- 

 ciations. 



d. Aspcn-Mrch Association and Eal)itat. 



This series develops from the beach and the waves fall from the 



ridges or low rock surfaces and leave the bare expanses. As the rock 



disintegrates, decomposes, and humus accumulates, a soil is formed, 



mainly in depressions or at the bases of the ridges, and from these 



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