1906 



FORESTRY AND IRRIGATION 



531 



necessary tools and implements and 

 prepare the soil. As much as is prac- 

 ticable at present is, however, being 

 done, pursuing the general plan fur- 

 nished, "following along the numerous 

 ridges, plowing a belt a short distance 

 from the military crest, with the inten- 

 tion of planting from three to five 

 rows of trees in each belt. The total 

 length of these belts, when completed, 

 will be betwen twelve and fifteen miles 

 and the belts will contain about fifteen 

 thousand broad-leaved trees and about 

 five thousand pine trees. The latter will 



be furnished by the Bureau of For- 

 estry, and the former will have to be 

 purchased from nurserymen in this 

 state and in Nebraska. . . . It is 

 also proposed to plant many thousand 

 acorns, blackberries, pignuts, etc., on 

 the slopes of the ravines below the rim 

 rock. This plan pursued systematical- 

 ly and intelligently for several years, 

 will greatly increase the military value 

 of the reservation and, incidentally, 

 this plan will also beautify the reser- 

 vation and, in time, bring some return 

 in fuel." 



STRENGTH AND STIFFNESS OF WOOD 



How It Is Affected by Moisture Experiments by Forest Service 



"WERY little is definitely known 

 * about the influence of moisture on 

 the strength of wood, even by those 

 experienced in handling the material. 

 Since the whole subject is one of great 

 importance, the Forest Service has 

 been making a thorough study of it 

 during the past three years and is 

 about to publish the results of its in- 

 vestigation in an exhaustive technical 

 bulletin entitled "Effect of Moisture 

 Upon the Strength and Stiffness of 

 Wood." 



The chief points presented by the 

 study are: 



i. The relation of moisture to 

 strength follows a definite law which 

 can be graphically expressed. Proper 

 drying very greatly increases the 

 strength of all kinds of wood, the 

 amount of increase in strength de- 

 pending upon the species and the dry- 

 ness. The increased strength given to 

 green wood by thoroughly drying it is 

 so great that it will surprise many, 

 tor example, the strength of a piece 

 of unseasoned red spruce may be in- 

 creased over 400 per cent by a thor- 

 ough drying at the temperature of boil- 

 ing water. Strength decreases again, 

 however, as the wood reabsorbs mois- 

 ture. Air-dried wood, protected from 

 the weather, and containing 12 per 

 cent of moisture, is from 1.7 to 2.4 



times stronger than when green, vary- 

 ing with the species. Stiffness is also 

 increased by drying. These conclu- 

 sions, however, are drawn from small- 

 sized pieces not exceeding 4 by 4 inch- 

 es in cross section such as are used in 

 vehicle work, tools, etc. Large tim- 

 bers require years of drying before the 

 moisture is reduced to the point where 

 strength begins to increase. It must 

 also be taken into consideration that 

 more or less checking always occurs 

 when large timbers dry ; and if this 

 checking is excessive it may cause 

 weakness to counterbalance, partially 

 or entirely, the strength gained in dry- 

 ing. Consequently, it is not safe to 

 assume that the average strength of 

 large, so-called seasoned timbers is 

 much greater than that of green or 

 wet ones. 



2. The fiber saturation point of a 

 number of species has been determined. 

 This point, which varies with condi- 

 tions and species of wood, designates 

 the percentage of water which will sat- 

 urate the fibers of the wood. It has 

 been found that, under normal condi- 

 tions, wood fiber will absorb a definite 

 amount of moisture ; beyond this the 

 water simply fills the pores of the 

 wood like honey in honeycomb. Only 

 that water which permeates the wood 

 fiber has an influence upon the 



