ECOLOGY OF ISLE ROYALE. ' 141 



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 laiquatic and shore associations. There is nothing in their 

 range to suggest their arrival earlier than the forest association. Tak- 

 ing 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 fre- 

 quented different situations, — thie forest kinds occupying the slopes 

 and drier valleys, and the others the openings. 



e. The Climax Association or FormaUon and HaMtat. 



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 association, 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 spruces. The climax association is the condition of ad- 

 justment toward which all societies move under the present conditions. 

 For this reason the earlier stages, conditions and associatioins of tlie 

 climax have been outlined in the preceding discussion. 



In the dominant forest the dense shade prevents an extensive ground 

 cover of herbaceous plants; and although Ground Hemlock is abundant 

 locally, yet in places the forest floor is quite open and free from lower 

 shrub growth. The remarkable preservation of trails or roads through 

 such tracts shows clearly how slowly changes take place. Such a 

 habitat must be relatively equable in its temperature and moisture 

 relations. 



Geographically speaking, the primary characteristic of the climax is 

 its relative staMlity, due to a dominance or relative equilibrium pro- 

 duced by the severe environmental and biotic selection and adjustment 

 throughout the process of succession. 



At this point attention should be called to the fact that dominance 

 is a resultant of an equilibrium produced by neutralizing or overcoming 

 other forces and influences. We may think of the process of succession 

 as a stream of forces whose development may be compared with the 

 transformation of a drainage line, — such as, for example, that of a 

 rivulet into a creek, and then. into a river. The stream and the char- 

 acter of the gi-ound mutually influence each other and the course fol- 

 lowed is a resultant of the mutual adjustments. The stream is deflected 

 by one condition and then another, just as succession varies with local 

 conditions; yet the water continues to run down grade and seeks an 

 equilibrium, and similarly, biotic succession continues on its course de- 

 flected here and there by local influences, jet forever tending toward a 

 state of biotic equilibrium. The dominance of the climax society or 

 formation, considered as a process rather than a product, has much in 

 it that is analogous to the dominance produced by the process of base- 

 leveling. 



The characteristic birds of the climax forest are: — the Chickadee, 



