24 FOREST COMMISSIONER'S REPORT. 



over which it is spread the volume of the yearly growth up to the 

 period of old age groivs steadily greater. 



A great number of interesting and valuable facts might be 

 brought out here as to the habits of tree growth, but for the present 

 purpose they would be only distracting. I shall merely ask and 

 answer the question — how much does a tree add to its bulk in a 

 year? The answer may be found more fully elsewhere with a 

 detailed account of how the figures have been obtained. As a 

 practical and usable figure it may be said that a large and healthy 

 spruce tree in the forest may add to its stem half a cubic foot of 

 wood a year. The larger it is the more wood it will grow up to 

 the period of decline, while young trees even though the rino- of 

 wood may be much thicker than in the larger tree, grow compara- 

 tively but a trifling amount. Ordinary sized trees in our culled-over 

 forests, such as are, say 10 to 14 inches iu diameter, breast high, 

 might grow from a quarter to a half of a cubic foot a year. The 

 test of the matter is the crown. If that is large, thick and free, 

 growth may be expected whatever the size of the trunk. The 

 crown indeed, its condition and the access it has to light, are the 

 chief factors in the growth of a tree. The supply of moisture 

 comes next, too much or too litlle being alike injurious. Of the 

 mineral constituents of the soil trees require but little ; and it is 

 seldom that a spruce tree when there is enough for foothold, will 

 not find also a supply of mineral food. 



Leaving the individual tree for the present, I pass on to other 

 branches of the inquiry. 



In all careful explorations of timber the acre is the basis of esti- 

 mate. The stand of sample acres is closel}' taken - unless indeed 

 the explorer have such skill as to be able to arrive with one step 

 at final results — and the yield of the whole tract estimated in com- 

 parison. Figures on growth therefore would be best put iu terms 

 of acres, and that has, in this work, been done. Jn this case as 

 before, the field notes on which I base my calculations were col- 

 lected in the employ of the national forestiy division. Recording 

 as they do not merely the dimensions and quality of the merchant- 

 able timber, but a count of every tree large or small on the tract 

 chosen, with a description of each species and size in trunk, crown 

 and general development, these figures tell vastly more than the 

 things we are now after. 



To illustrate by one case the mode of field work. On the third 

 day of January last with my companion, I brought up at Davis' 



