Forestry in Canada. 



91 



the leaves — all these have been put 

 forward in explanation and probably 

 each has an influence, but we are still 

 face to face with one of the most interest- 

 ing unexplained problems of nature. 

 The quiet, forceful and economical way 

 in which nature elevates her water 

 supply is no less a locked secret to the 

 scientist than it is to the city engineer 

 and the plumber. 



The leaf, the great digestive apparatus 

 of the tree, is not less important than the 

 root. Requiring sunlight to carry on 

 the process of disintegration of the 

 substances on which it feeds, it spreads 

 out its canopy of leaves arranged in- 

 geniously and methodically in such a 

 way as to present the largest surface to 

 the light. Coniferous trees make up for 

 the narrowness of their leaves by their 

 greater number. Carbon derived from 

 the air is the main food of the tree, so 

 that it requires little but moisture from 

 the soil and can therefore live on poor 

 soils, lands useless for agriculture. The 

 Norway pine and jack pine flourish on 

 sandy soil useless for other vegetation. 

 The white pine, the spruce, the maple, 

 may be found grasping the almost bare 

 rock with their roots and finding a 

 livelihood where other vegetation would 

 fail. 



The influence of light on tree growth 

 is one of the most important factors the 

 forester has to consider and the trees 

 have been classified as tolerant and 

 intolerant according to their ability to 

 grow in the shade. For Canadian species 

 the list might run as follows, commenc- 

 ing with those most tolerant of shade: 

 hard maple, beech, hemlock, spruce, 

 balsam, soft maple, birch, white pine, 

 black cherry, ash, bird cherry, poplar, 

 tamarack, jackpine, red pine. This 

 knowledge is important, for the forester 

 must give the degree of light which will 

 favor the species he wishes to bring in. 

 Spruce and pine will not flourish under 

 the hea^'y crowns of the hardwoods, and 

 spruce would have the advantage over 

 pine in heavy shade. 



The water, with traces of mineral 

 salts, coming from the roots, and the 

 carbon compounds from the leaves are 

 built up into wood cells, the active work 

 of tree building going on in the cambium 

 or outer cells of the wood next to what 

 is termed in general phrase the bark. 

 These active cells are large and thin- 

 walled and form the sapwood of the 



tree. The heartwood is formed of such 

 cells which have gradually thickened 

 their walls and contracted their aper- 

 tures and which are to all intents and 

 purposes dead. In the earlier years most 

 of the wood is sapwood, in the later 

 years the heartwood is the greater: and 

 as this latter is much more valuable for 

 lumber a strong argument is found in 

 this fact for allowing trees to grow to a 

 mature age. The annual rings, so charac- 

 teristic a feature and one which enables 

 the forester to determine the age of trees, 

 are the result of the diff'erence between 

 the active spring growth of cells with 

 thin walls and large apertures contrast- 

 ed with the wood of the later summer 

 with contracted thick-walled cells. 



When does the tree reach its best 

 development? With spruce and pine 

 the rotation adopted in Germany is 

 from sixty to eighty years, though trees 

 required for special purposes maj^ be 

 left longer. Trees which are now being 

 cut in the mills at Ottawa for lumber 

 will run between one hundred and two 

 hundred years of age. A growth under 

 forest conditions of an inch in diameter 

 in five or six years on an average is the 

 best that can be expected. 



"For Nature, also, cold and warm, 

 And moist and dry, devising long. 

 Thro' many agents making strong, 

 Matures the individual form." 



Examples of individual trees grown on 

 open lawns or other favored places in 

 short periods are not a criterion for 

 forest conditions any more than are 

 trees grown in wind-swept or other un- 

 favorable conditions. Growth will vary 

 under conditions of moisture, soil, etc., 

 but anyone who expects the renewal of 

 a spruce or pine forest in thirty years or 

 any such period is hugging a delusion, a 

 general acceptance of which would be 

 disastrous. 



Enemies of the Forest. 

 The forest has many enemies. Wounds 

 caused by fire or other agency give en- 

 trance to fungi, which finally work 

 through the tree, breaking down its 

 structure and destroying its usefulness, 

 as has occurred with a large extent of 

 poplar on the Riding Mountain Forest 

 Reserve. Insects have done a like 

 service for one of the few remaining 

 patches of spruce on that reserve. 



