silvicultural management of black spruce in minnesota 13 



Succession in Natural Stands 

 swamps 



Black spruce occupied extensive areas of swamp prior to settlement 

 and logging in Minnesota, chiefly because very few other tree species 

 were adapted to the poorly drained peat soils. This was quite the 

 reverse of the situation on uplands, where trees of many kinds grow 

 vigorously and display rather definite patterns of ecological succession. 



Black spruce is one of the first trees to invade primitive treeless 

 swamps, although it usually is slightly preceded by tamarack. Black 

 spruce also generally continues as the dominant kind of vegetation in 

 swamps through later stages when the peat soil is gradually elevated 

 by the further accumulation of organic matter and fertility condi- 

 tions are improved. In these more mature stages of swamps in Min- 

 nesota, there is some increase in the occurrence of balsam fir and paper 

 birch, but they seldom are of importance. Black spruce and its gen- 

 erally less numerous associate tamarack form a remarkably stable 

 forest type with no effective competitors over a wide range of condi- 

 tions of peat swamps. 



In some swamps tamarack seems to become established more readily 

 than black spruce. Although the fundamental reason for this differ- 

 ence is not apparent, tamarack sites in their most distinct phases almost 

 always can be distinguished by a rather abundant occurrence of 

 speckled alder (Alnus incana) in contrast to black spruce sites that 

 have shrubby vegetation composed mainly of heath plants, the most 

 common of which are leatherleaf (C hamaedaphne calyculata) and 

 Labrador tea (Ledum groenlandicum) . Gradations between spruce 

 and tamarack sites are common. Black spruce grows well on tam- 

 arack sites but does not become established readily. The distinction is 

 important because it accounts for many of the examples where spruce 

 has failed to regenerate on deforested or poorly stocked swamp land. 



There is another class of swamps in which black spruce occurs but 

 where northern white-cedar predominates. Since white-cedar is un- 

 able to endure as acidic soil conditions (7) , it is rather sharply limited 

 in occurrence. White-cedar is longer-lived and more shade-tolerant 

 than black spruce; accordingly, black spruce has little chance of 

 reproducing under natural conditions in swamps where vigorous 

 white-cedar is present. 



UPLANDS 



In the spruce-fir type, where black spruce occurs most frequently on 

 upland soil, almost all native tree species are present to some extent, 

 but balsam fir, paper birch, quaking aspen, and white spruce are most 

 common. It was concluded by Cooper (9) that on Isle Roy ale, Lake 

 Superior, balsam fir, paper birch, and white spruce together formed 

 the dominant elements of the plant association that succeeded all other 

 tree species under natural conditions. More recently, Lee (&£) in 

 studying forest successions at Lake Itasca, Minn., decided that balsam 

 fir and white spruce would form the climax forest in that locality. 



It is significant that black spruce has not been considered a member 

 of the climax forest. It indicates that black spruce has less natural 

 ability for self-perpetuation in the spruce-fir type than it has in 

 swamps. 



