VEGETATION 
Vegetation is important to bird 
life, and in a large measure deter¬ 
mines the variety of habitats avail- 
*t>le <U> . Isle Royale has two basic 
climax forest types, sugar maple- 
yellow birch and spruce-fir-white 
birch. The relations between these 
two types were studied by Cooper (4) 
and Linn ( 37 ) * 
Extensive fires have reduced 
climax forests to about half of the 
island. Succession on fire-denuded 
areas usually proceeds through an 
aspen-white birch cover to climax 
conditions. Two major periods of 
burning are evident: one dates from 
the mining era of about 100 years 
ago, when extensive fires were set 
to denude the rock strata to facili¬ 
tate search for copper, and the 
other from 1936, when about a quarter 
of the island burned in a series of 
fires of uncertain origin. 
In addition to the major cli¬ 
maxes, a significant part of the 
island is occupied by bog forest 
types, mainly white cedar and black 
spruce. 
The island's woody vegetation 
currently may be grouped into five 
general types on the basis 
of pres- 
ent cover conditions (9): 
Per¬ 
Sq. 
cent 
Mi. 
l.Sugar maple-yellow birch 
9 
20 
2.Spruce-fir-white birch 
36 
73 
3 .Aspen-birch-conifer 
25 
52 
(100-year-old burns) 
4.Aspen-birch (1936 burns) 
23 
50 
5.Bog forests 
7 
15 
The sugar maple-yellow birch 
climax forest type is largely con¬ 
fined to the higher slopes of the 
Greenstone Ridge on the southwestern 
third of the island, extending about 
10 miles from near the head of Wash¬ 
ington Harbor to Lake Desor (fig.l). 
Of the two dominant species, sugar 
maple is much more abundant. Trees 
of both species are often overmature, 
and specimens 20 inches in diameter 
are common. The understory consists 
of a dense growth of sugar maple 
reproduction 2 to 10 feet high, with 
some mountain ash, mountain maple, 
American yew, beaked hazel, yellow 
birch and Canadian honeysuckle. In 
places where drainage is poor, white 
cedar and balsam fir are also found. 
Aspen, white birch, juneberry, fire 
cherry, white spruce, red-berried 
elder, roundleaf dogwood, black ash, 
and an occasional virgin white pine 
occur scattered in this type. 
In the spruce-fir-birch climax 
forest type, balsam fir is most 
abundant, with white birch and white 
spruce scarce to common (figs. 2, 3, 
and 4). Parts of this type which 
have been subjected to fires most 
recently also contain scattered, 
relict aspen. This type is main¬ 
tained by the cooling influence of 
the lake water, and therefore is 
found on the lower slopes of the 
island shore. The northeast section 
of the island where most of the land 
is quite close to water, is covered 
largely by this type or by serai 
stages leading to it. Low vegeta¬ 
tion is usually a mixture of moun¬ 
tain ash, mountain maple, willow, 
ground hemlock, red-osier dogwood, 
mountain alder, and highbush cran¬ 
berry. 
The aspen-birch-conifer type 
is largely confined to the north¬ 
eastern section of the island, where 
there were extensive fires in the 
last century (fig. 5). This type, 
intermediate between the aspen-birch 
and the spruce-fir-birch climaxes,is 
characterized by extensive, pure, 
even-aged stands of aspen and white 
birch. Balsam fir and white spruce 
are invading rapidly in some areas, 
while white cedar and white pine 
occur occasionally. Ground vegetation 
3 
