MICHIGAN ACADEMY OF SCIENCE. 
73 
lias been a rather high representation of Firms strobus and P. resi- 
nosa. The depletion of the soil by tire has been the greatest single 
factor in overturning the normal genetic trend. 
When hardwood land is severely burnt over, the humus is burnt out 
of the soil and the succession that is instigated goes thru the fireweed 
associations to aspens or occasionally thru Finns banksicma to Finns 
strobus. If the burn is not so severe, fireweeds appear to be almost im- 
mediately succeeded by birch with some aspen, which in turn is quite 
likely to be followed by hardwood, altho this is not always the case. 
In case the burn is light, hardwood succeeds hardwood, altho there 
may be a number of fireweeds and seedling birches present for a time. 
Altho hardwood species — represented by both seedlings and older 
trees— are not infrequently present in the Picea-Abies and the Thuja 
bogs, as they occur in this region, there is no evidence to show that any 
definit succession is taking place. On the other hand the greater part 
of the evidence goes to show that no succession is taking place. It is 
presumed that in the case of a general change in water , table level 
succession might take place because the tension line between hardwood 
and Thuja is very sharp and agrees almost perfectly with a definit liiglit 
around each bog where these associations occur in juxtaposition. 
last of the Species of the Beech-Maple Association: 
A. Trees. 
DOMINANT SPECIES. 
Fagus grandifolia m and s. 1 Betula 1u tea m and s. 
Acer saccliarum m and s. Tilia americana . m and s (few old 
Tsuga canadensis m and s. trees). 
SECONDARY SPECIES. 
A b ies b a ha 1 n ea m a n d s . 
Bet ui a tent a, m and s. 
Fraxinus americana m and s. 
Populus balsam if era (near edge) m. 
litmus americana (few) m and s. 
Fr unus serotin a ( few ) . 
RELIC SPECIES. 
Quercus rubra (old trees). 
Finns strob'us (old trees). 
Acer rubrum (few). 
Th uja occidentaVis. 
Picea canadensis. 
Betula alba pa pgr if era (old trees). 
Fraxinus nigra (few young). 
Primus pcnnsylvaniea (few). 
INVADING SPECIES. 
(In clearings or openings only.) 
Finns strobus (seedlings). 
Quercus rubra (seedlings). 
Betula alba . papyrifera (seedlings 
and young trees). 
Fopulus trermdoid.es (seedlings). 
’“m’^matur trees, “s”=seedlings. 
Populus gran d i dent a ta. 
Primus pennsylvan ica. 
Acer saccliarum. 
Fa g i is g i 'a i id i fo lia. 
(Seedlings and young trees.) 
