320 



FORESTRY AND IRRIGATION. 



August, 



Thus the forest is divided into three 

 classes dominant, intermediate, and 

 suppressed trees. This struggle for ex- 

 istence goes on during the entire life of 

 the forest, and is apt to so reduce the 

 growing space of each dominating tree 

 that it cannot reach its fullest develop- 

 ment, and on account of crowding is 

 likely to assume a long, lanky shape, 

 which is very easily damaged by wind 

 and snow. It is this state of affairs 

 that the owner should strive to obviate 

 by thinning his trees. Thinning is the 

 cutting out of such tree-growths as in- 

 terfere with the healthy development, 

 and hence the future value, of the crop. 

 This form of thinning is termed the 

 " weeding " out of the undesirable 

 trees. 



A single tree growing in the open 

 and in the complete enjoyment of light 

 will develop a full crown and root sys- 

 tem and lay on a maximum volume of 

 wood, but growth under these condi- 

 tions has several serious drawbacks : 



I St. Trees growing in this manner do 

 not always produce the greatest volume 

 of wood per acre. Although every tree 

 in a crowded woods has a smaller vol- 

 ume than the isolated one, yet, owing 

 to the greater number of trees, the 

 crowded stand generally has a larger 

 total volume per acre, and therefore 

 greater stumpage value. 



2d. Isolated trees usually grow short 

 or crooked, while trees in thick woods 

 are, as a rule, straight. 



3d. Trees in the open generally have 

 branches low down on the trunk ; con- 

 sequently they produce knotty and less 

 valuable timber. Moreover, open stands 

 are not apt to improve the fertility of 

 poor soil on account of exposure to the 

 light, which dries out the moisture; 

 hence open stands can be grown best 

 only in naturally fertile soils. 



These few conditions govern profit- 

 able growth in all localities. Thus 

 while in one case it would be proper to 

 remove all suppressed and dominated, 

 and even a part of the dominating, 

 trees, in another case it would be nec- 

 essary to look carefully after all of these 

 classes in order to secure the maximum 

 growth and the highest timber value 

 from the land. 



Certain important changes are gradu- 

 ally taking place in the growth of trees 

 in the forest, both individually and col- 

 lectively. There are changes in the soil 

 in which they grow, in the surrounding 

 atmosphere, and changes wrought even 

 upon the inhabitants in the neighbor- 

 hood These changes are chemical and 

 mechanical. A growing tree takes from 

 the soil the elements that are essential 

 to its development, but restores them to 

 the soil through its fallen leaves and 

 branches in the form of carbonaceous 

 and nitrogenous matter. Thus, under 

 normal conditions the soil grows richer 

 and capable of supporting larger and 

 more luxuriant forests. The mechanical 

 changes are more easily traced. The 

 roots of trees change the composition of 

 soil b}' forcing their way into it, thus 

 disintegrating the rocks and earth and 

 allowing the free access of air and water. 



In dividing the trees of a forest into- 

 classes an account must be taken of the 

 dead trees. These should be removed 

 at every thinning, as they can be of no- 

 benefit to the other classes, but may be 

 a constant source of danger from insects,, 

 fungi, and, in many cases, fire. 



All thinnings are carried on with one 

 of two objects in view : first, the pro- 

 duction of the greatest quantity of ma- 

 terial ; second, the production of the 

 highest quality of timber. The means- 

 of attaining these ends differ consider- 

 ably. 



Experience has taught that the great- 

 est quantity of timber is produced in the- 

 shortest time by the vigorous develop- 

 ment of the dominating trees. These 

 are removed and converted into lumber 

 as soon as the undergrowth is of suffi- 

 cient density to protect the soil (Fig. i ) . 

 The first thinning is made as soon as the 

 struggle for existence commences that 

 is, when it is found that the trees are 

 contending with each other for light and 

 space. If the owner of the woodlot has 

 gone over his land in the earh' stages of 

 its tree growth and weeded out the un- 

 desirable trees, this fir.st thinning ma)' 

 be delayed till the tenth or fifteenth 

 year, when the trees taken out may be 

 utilized for firewood or temporary fence 

 posts. The thinning should be heavy 

 enough to give the trees that remain the 



