106 NEW BRUNSWICK FORESTRY CONVENTION 



by Mr. H. S. Graves, in connection with his studies, prosecuted inv 

 the Adirondack region, under conditions which give them exceptional 

 value. 



In regions of dense forest and cool Climate, a deep layer of humus, de- 

 rived from the decaying foliage, accumulates upon the forest floor and serves 

 to retain enormous volumes of water, which is liberated slowly, and finds its 

 way to the adjacent streams. If now such a forest be thinned, and freer 

 circulation of air and the greater access of the sun's rays serve to bring 

 about a more rapid disintegration of the humus, with the result that an in- 

 creased amount of plant food becomes available, while the drainage of the 

 stored water will permit the roots to be influenced by a somewhat higher 

 temperature. These conditions serve to explain the immediate increase of 

 growth which is consequent *upon them, but it must also be evident that 

 as the humus is gradually exhausted, the effect will be a diminishing 

 one, and it must finally cease altogether. How long a time will 

 intervene before this takes place is not altogether certain, but Prof. Hartig r 

 of Germany, estimates it, under favorable conditions, at a limit of ten years. 

 In addition to these influences, it is also true that the thinning of a forest 

 tends to the development of a larger and more efficient root system for 

 the absorption of food supplies, and, similarly, to the development of 

 a more perfectly - organised system for the digestion of such food materials 

 as may be furnished by the roots and leaves. There are, in other worda, 

 more perfect conditions for the individual development, and this is expressed 

 in an increased growth, both in diameter and height. 



AVERAGE RATE OF GROWTH IN DIAMETER 



From a critical study of 1,593 trees, Mr. Graves has been able to reach 

 the conclusion that the effect of thinning produces accelerated growth to the 

 extent of 18 per cent., and that while, in the original growth, it re- 

 quired nine years for an increase in the diameter of one inch, the thinned 

 timber required only five years to attain the same increment. 



From these and similar studies, it has been possible to determine 

 the periods of time within which a forest may recover from the effects 

 of the first cutting, according to the dimensions of the trees left, and these 

 data are reduced to tabular form, in what are designated as Yield 

 Tables. 



