138 Adams, Ecological Succession of Birds. [^"'^1 



The easily inflammable character of these conifers, even \\lien in 

 a green condition, makes it Hkely that natural causes, such as light- 

 ning or marsh gas (cf. Penhallow, '07), may haA'e been influential. 

 The proximity of the gas supply and the conifers is of interest as 

 this may influence their liability to fire and thus to this sort of 

 reversal of conditions. Thus liability to fires is rather character- 

 istic of the region, and man's influence has tended merely to rein- 

 force rather than to introduce this feature. Thus it seems probable 

 that fires have been a factor in supplementing the natural park-like 

 openings. In addition to the burned areas found upon Isle Koyale, 

 other limited open areas are due to cultivation and are kept open. 



The birds characteristic of the more open situations are the Sharp- 

 tailed Grouse, Song and Chipping Sparrows, Flicker, and the Purple 

 Finch. The Grouse is a Plains form, is near its eastern limit, 

 and is perhaps a late arrival upon the island. The other species 

 are wide ranging in the Canadian coniferous forests but are not of 

 such northern range as the aquatic and shore associations. There 

 is nothing in their range to suggest their arrival earlier than the 

 forest association. Taking all the birds of the openings together, 

 it is not improbable that they arrived at about the same time as 

 those of the forests, but frequented different situations, — the 

 forest kinds occupying the slopes and drier valleys, and the others 

 the openings. 



e. The Climax Association or Formation and Habitat. 



The climax association should not be considered in such a way 

 as to lead one to think that it is distinct from the other associations. 

 It belongs to all of them as the end of their series under existing 

 biotic and environmental conditions. Thus the aquatic associa- 

 tion, through the bog conifers, is transformed into the Balsam- 

 spruce association; and from the beach through the aspen-birch 

 association again to the balsams and s]:>ruces. The climax asso- 

 ciation is the condition of adjustment toward which all societies 

 move under the present conditions. For this reason the earlier 

 stages, conditions and associations of the climax have been outlined 

 in the preceding discussion. 



In the dominant forest the dense shade prevents an extensive 



