10 



CIRCULAR 791, U. S. DEPARTMENT OF AGRICULTURE 



ing conditions for spruce seem to be similar to those on moist mineral 

 soil. 10 The natural development of the peat has also been disturbed 

 repeatedly and extensively by a number of factors, both natural and 

 man-caused, including forest fires, and raising or lowering of the water 

 tables. Therefore, swamps are exceedingly complex and diverse for- 

 mations as to site quality for the growth of black spruce or other trees. 

 No other native Minnesota tree, except tamarack, can endure such a 

 wide range of growing conditions as that regularly exhibited by black 

 spruce in different swamps or different parts of the same swamp. 



Figure S. — Black spruce stand in a swamp. The wide right-of-way is caused hy 

 an agricultural drainage ditch at the right. The ditch has been abandoned, as 

 have many similar ones in Minnesota. 



The characteristic pattern of productivity in swamps is for the 

 best growth to be at the border and progressively poorer growth to- 

 ward the center. Unless the slope of the adjoining upland is abrupt, 

 there usually is a border transition zone which is neither true upland 

 nor true swamp. In northeastern Minnesota the swamp border types 

 sometimes are as much as 30 or ±0 acres in size. In such instances 

 they commonly are underlain with boulders. Almost invariably the 

 best growth occurs in this band of "swamp border." The decline in 

 growth rate toward the center of a swamp may be steplike or regular, 

 slow or fast. In small pocket swamps, which are common in north- 

 eastern Minnesota, the average heights of dominant trees about 80 

 years in age often range from 60 feet down to 20 feet within a distance 

 of 150 feet. In larger sw T amps, the transition in site quality ordinarily 



10 The term '•swamp*' is used throughout this paper to include all peat forming 

 areas, as has been advocated by Waksman {29), in the belief that attempts to 

 differentiate between swamps, bogs, muskegs, moors, etc., are inexact and 

 confusing. 



