FOREST MENSURATION. 175 



by considering 1,000 cubic feet as the equivalent of from 

 4,000 to 7,000 feet board measure, according to the size 

 of the trees, young growths giving much less than old 

 growths. 



The Conversion of Cubic Feet Firewood into Cords is 

 accomplished by the use of the factors which experience 

 has shown to be practically accurate. A cord of wood 

 piled up occupies 128 cubic feet of space, but on account 

 of the shape of the sticks much of this is air space, and 

 the actual wood content much less than 128 cubic feet. 

 In Germany a cord has been found to contain 83.2 cubic 

 feet of wood. In Saxony, Dr. Schenck says that eighty-six 

 cubic feet make a cord of ordinary firewood, and that 

 25.73 cubic feet of branch stuff will pile up to a cord. At 

 the Minnesota Experiment Station by actual measurement 

 of round, straight sticks, a cord has been found to contain 

 as high as 102 cubic feet. This factor of 102 cubic feet 

 may apply very well to straight, well- trimmed spruce, 

 tamarack, etc., free from knots and limbs, but will be too 

 high for Oak and similar wood, which is inclined to be 

 more crooked, and does not pile so closely. A cord of small 

 oak averaging 3.4 inches in diameter and ranging from 

 1.5 to 7.5 inches, consisting of 274 four-foot sticks, meas- 

 ured 69.67 cubic feet. Averaging these two extremes, 

 85.85 cubic feet is found in a cord of mixed wood, corre- 

 sponding very nearly to the figure given by Dr. Schenck. 



RATE OF GROWTH. 



The Accretion of a Tree is the Increase in Wood Con- 

 tent as the Result of its Activity During the Growing 

 Periods. The rate of growth is indicated by the increase 

 in diameter, in height, or in mass, and may be considered 

 as annual or as periodic. The diameter accretion is 

 equal to twice the thickness of the annual rings for the 



