522 JOURNAL OF FORESTRY 



total height of 70 feet in that time, while balsam will attain a diameter 

 of 11 inches and a total height of 83 feet. Density figures are only 

 available for spruce. In 100 years, the number of trees per acre is 

 reduced on Quality I sites to 415 from over 2,000 trees at 20 years of 

 age. Yield data exist for both red spruce and paper birch. The former 

 will yield on good sites 7,400 cubic feet in 100 years, while paper 

 birch will give 5,500 cubic feet with an understory of spruce ready to 

 take its place when the intolerant paper birch is cut out. 



Northern Hardwood Type 



The northern hardwood type in which the characteristic species are 

 red spruce, beech, yellow birch, and sugar maple has a slightly longer 

 growing season than the spruce type. This is natural because it is 

 located just below the spruce type in altitude. The total annual pre- 

 cipitation averages slightly less. Forty inches is a good figure for the 

 type throughout its range, although it ranges from 30 inches in the 

 Lake States to 45 inches in Maine and New Hampshire. The run-oft 

 will be approximately the same as in the spruce type because the 

 higher temperatures and longer growing season are offset by the less 

 acute slopes. Likewise there is little difference in the evaporation of 

 the two types, although there would naturally be slightly more from 

 the hardwood type on account of the longer growing season. The 

 total amount of available moisture is unquestionably less than in the 

 spruce type on account of the lower total annual precipitation and the 

 slightly greater evaporation. However, the vigor with which spruce 

 grows in this type indicates that there is comparatively little difference 

 between climatic conditions. What advantages there are, are in favor 

 of the hardwood type with its longer growing season which permits 

 greater diameter and height development. 



On account of the lack of pure stands yield figures for the hard- 

 wood type are neither abundant nor satisfactory. As yet we have 

 done comparatively little to determine yields of our mixed stands. 

 Mr. Hawes has, however, worked up some yield figures for Vermont 

 hardwoods from which it is estimated that they will yield in 100 years 

 7,000 cubic feet. The Forest Service figures on aspen also permit of 

 an estimate of the possible returns from this species in the same 

 length of time. Thirteen thousand cubic feet seems to be a conserva- 

 tive figure for aspen in spite of the fact that it is an intolerant species 

 and the density is low. It is improbable that there will be more than 



