BATE OF INCREASE IN TIMBER. 161 



forty feet high. But such trees are then growing very fast, 

 and as the approximate increase in volume of the tree 

 is as the square of the proportionate increase in diameter 

 and the waste in working greatly decreases with the size 

 of the trees, the cutting of them at such an early age 

 would be at a loss of future profits. Such trees have very 

 little, if any, heart wood, and yet this kind of timber 

 is being grown and marketed in many of the Eastern 

 States. In fact, there is very little heart to any of the 

 pine now cut in the New England States, as it is practi- 

 cally all young second growth, and is generally marketed 

 about as soon as it attains sufficient size to be salable, 

 without regard to the fact that it is then making its most 

 rapid growth. 



From careful observation, the Experiment Station 

 of the University of Minnesota estimates that on land 

 adapted to the White Pine, with a thick growth of this 

 kind of trees eight inches in diameter, the annual increase 

 should be about fifty cubic feet, or 500 feet board measure, 

 per acre. In some cases this rate of increase has been 

 more than doubled, but under ordinary good conditions 

 not over one-third as much increase need be expected. 



The Thickness of the Annual Rings on trees varies 

 with the conditions under which the trees make their 

 growth, and is therefore a good index to these conditions. 

 Trees that are crowded so that they make a very rapid 

 upward growth form very thin rings, and when this up- 

 ward growth ceases owing to the removal or suppression 

 of surrounding trees much thicker rings are formed. Trees 

 that are grown in the open, produce throughout their 

 lives thick annual rings, which vary in thickness accord- 

 ing to varying climatic conditions. Those of the White 

 Pine vary in thickness from one-sixteenth of an inch or 

 less in trees that are severely crowded to one-third of 

 an inch in open-grown trees in good soil. Willows some- 



