MICHIGAN ACADEMY OF SCIENCE. 
C9 
INVADING SPECIES. 
Tsuga canadensis. 
Pi mis strobus. 
Pic ea c a na den s i s . 
Betula lutea (young and old trees). 
Tiiia americanci (very few but one Pyrus americana. 
tree large) . 
Betula alba pap yr if era. 
Popuhis ire mul aides. 
The Picea-Abies Association. 
This more northern association may have been better represented in 
the region at an earlier date, but at the present time it is suggested by 
the extensive development of white spruce (with some black spruce) 
and balsam near the upper end of the gorge which opens into Burt 
Lake. The ground is kept water-soakt by the cold springs at the 
head of the gorge but differs from the typical bog situation in being 
fairly rapidly drained. 
As mentioned above, the extensive development of spruce and balsam 
characterize the association. Mixt in somewhat with them but particu- 
larly above their upper margins on the sides of the gorge are a number 
of large red and white pines. On raised portions between the springs 
and between the streams that flow from some of the different springs, 
there are some large-sized trees of Betula lenta , Betula lutea, Tiiia, 
americana, Acer saccliariim. and seedlings of these same trees, but 
particularly Acer saccharum together with seedlings of Fraxinus 
nigra and Fagus grandifolia. Towards Burt Lake the association grades 
off into the typical cedar bog. Thruout the association, but best de- 
velopt near its margin with the cedar bog, is the mountain maple ( Acer 
spicatum) . There is virtually no ground vegetation in the denser parts 
of this association. 
From the character of the seedlings and young trees that are present 
the higher parts of this association are tending towards a hardwood 
forest while the lower parts will remain a mixtur of this association and 
the cedar bog. 
Lumbering and light burning in this association lead to the instiga- 
tion of the fi reweed association followed almost immediately or at 
least within a year by the bramble association which in due course of 
time is replaced either by hardwood in the drier, better drained situa- 
tions or by Picea-Abies in the lower, wetter situations. No severe burns 
were found in this immediate area but it can probably be safely pre- 
sumed that in the advent of a severe burn the drier, better drained parts 
would go to aspen and i hen to pine, while the lower, wetter parts would 
become dominated by cedar bog species, possibly with, and probably 
without a tamarack stage. 
List of the Species of the Picea-Abies Association. 
DOMINANT SPECIES. 
Pi cea canadensis. 
A bies balsamea. 
Petal a lutea. 
