SILVICULTURAL MANAGEMENT OF BLACK SPRUCE IN MINNESOTA 27 



F-377810 



Figure 18. — Black spruce layers that originated from stumps in foreground. 

 The "Mother" trees were felled 6 years previously. The young trees are now 

 growing vigorously. 



GROWTH AND YIELD 



Black spruce is a small and slow-growing but moderately long-lived 

 tree (fig. 19) . A height of 85 feet is exceptionally tall for this species 

 in Minnesota and diameters seldom exceed IT inches at breast height. 

 The greatest ages attained are about 250 years. However, most trees 

 are considerably shorter, smaller in diameter, and younger than these 

 near-maximum figures. Typical merchantable trees are 40 to 65 feet 

 tall, 6 to 12 inches d. b. h., and 60 to 150 years old. 



The height growth rate of upland black spruce while young is slow 7 er 

 than those of its common competitors but a little faster than that of 

 white spruce. In a planting experiment using 2-year-old seedlings, 

 on the Kawishiwi Experimental Forest, black spruce and white spruce 

 had average heights of 1.9 and 1.4 feet respectively 4 years after field 

 planting. In an 18- to 20-year-old mixed natural stand in the same 

 locality, the average height of the black spruce was 9 feet and the 

 white spruce 8.1 feet. Many of these trees had been overtopped by 

 aspen and birch of the same age. The tallest individual black spruce 

 was 21.5 feet in contrast to 14.5 feet for white spruce. After the 

 age of 20 years, white spruce gradually catches up with and finally 

 outstrips black spruce on upland soils. At the age of 70 years, white 

 spruce is likely to exceed black spruce in height by about 10 or 15 

 feet. 



Growth of unsuppressed trees at early ages in the more fertile 

 swamps is only slightly slower than on typical upland sites. Numer- 

 ous counts of annual rings at d. b. h. and at the ground line have 

 shown an average difference in age of 13 years. Under heavy shade 

 or on poor sites height growth is much slower ; it is not at all unusual 

 to find seedlings 15 years old that are only 6 to 12 inches tall. 



