136 Adams, Ecological Succession of Birds. [\d11 



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. 

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

 forest may be perfectly continuous, and thus there will be a series 

 characterized by the dominant conifers. In places Arbor Vitse 

 may form the dominant swamp forest, but this is only a variation 

 in the conifer dominance. With improved drainage or the accu- 

 mulation of vegetable debris, these habitats become converted into 

 the Balsam-spruce climax forest and hence the environmental 

 d}Tiamic tendency. 



As the forest encroaches upon the open bogs the Tamarack, 

 Black Spruce, Arbor Vitse, Cassandra, I^abrador Tea and alders 

 are accompanied by birds characteristic of this early stage; such 

 as the Red-breasted Nuthatch, Yellow-bellied Flycatcher, Golden- 

 crowned Kinglet, Cedar War^ving, 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. Siill 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 associations. 



d. Aspen-hircli Association and Habitat. 



This series develops from the beach as 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 it tends to encroach upon the open places with a zone of Jack 

 Pine, aspens, or White Birches. These areas are largely strips 

 along the crests of ridges or small park-like openings on rather 

 level rock. In no case are these single areas large, so that the 



