1913] COOPER—ISLE ROYALE II 
climax forest of that portion of the northeastern conifer region 
under consideration; in other words, that upon Isle Royale it is 
the final and permanent vegetational stage, toward the establish- 
ment of which all the other plant societies are successive steps. 
It is the “climatic” forest of the region, permanent while the 
climate remains essentially as now. 
The evidence in support of this conclusion lies along four lines: 
(1) extreme mesophytism of the forest; (2) its uniformity of 
development; (3) all successions lead to it; (4) maintenance of 
equilibrium. These lines of evidence will now be considered in 
order. 
1. Mesopuytism.—The balsam-birch-white spruce forest is the 
most mesophytic of all the plant societies of the island. The truth 
of this statement will appear during the discussion of other points 
and so no further treatment is necessary here. 
2. UNIFORMITY OF DEVELOPMENT.—In all places where it 
occurs, whether upon rock surfaces or reclaimed bogs, upon the 
part most recently emerged from the lake or upon the highest 
ridge, the dominant forest is essentially uniform in character. The 
tree species are the same, and they bear everywhere the same 
relations to each other. 
3. ALL SUCCESSIONS LEAD TO THE BALSAM-BIRCH-WHITE SPRUCE 
FOREST.—In a later portion of this paper the various successions 
are treated in detail, and it is shown that all end with the establish- 
ment of the balsam-birch-white spruce forest. In other words, 
those phases of the vegetation that are not uniform in character 
with the main forest mass are plainly tending toward uniformity. 
The successions upon Isle Royale may be classified as follows: 
A. Primary successions 
I. Xerarch* successions 
1. The rock shore succession 
2. The beach succession 
* The terms xerarch and hydrarch are here used for the first time, for the purpose 
of indicating a natural and important classification of plant successions. The former 
is applied to those successions which, having their origin in xerophytic habitats, such 
as rock shores, beaches, and cliffs, become more and more mesophytic in their succes- 
sive stages; the latter to those which, originating in hydrophytic habitats such as 
lakes and ponds, also progress toward mesophytism 
