TIMBER CRUISING 



1487 



cent of the tract. Where the spacing is 5 chains, 20 per 

 cent of the tract is covered. For any but very small 

 areas, a 20 per cent cruise is sufficiently accurate even 

 for high priced stumpage. 



The second brings in the use of "Volume Tables." A 

 volume table for any kind of timber, Douglas fir, for 

 example, is a table that gives the average scale for 

 Douglas fir trees according to diameter breast-high (1. e. 

 4J/2 feet above ground) outside the bark, and merchant- 

 able length. Thus, from a volume table prepared by 

 the United States Forest Service, one can read that a 

 fir 36 inches in diameter, and having a log length of 170 

 feet, contains on the average, 2,020 feet if scaled with the 

 Scribner Rule. The volume table is made up from a 

 large number of measurements of trees of all sizes, taking 

 the diameter breast-high outside the bark (which can 

 always be actually measur- 



ed, and, therefore, does not 

 need to be estimated) and 

 the scale of the whole tree 

 by logs according to the log 

 rule. Of course, these meas- 

 urements are taken from 

 felled trees, and the scale 

 of the trees 36 inches in 

 diameter breast-high, for 

 instance, is averaged, so 

 that one volume figure is 

 obtained that will apply to 

 all trees of that species 36 

 inches in diameter and 

 within a certain range of 

 merchantable height. 



In using a volume table it 

 will be borne in mind that 

 figures are average 

 figures, and that local 

 measurements must always 

 be taken on each tract so as 

 to determine whether the 

 timber on the particular 

 area cruised will scale bet- 

 ter or poorer than the aver- 

 age shown by the table, 

 poorer. 



From 80 to 95 per cent of all sound trees of any species 

 within any type of stand fall within a normal range of 

 variation as to form of bole, and the relationship between 

 base diameter and average volume can readily be deter- 

 mined by taper measurements on a comparatively small 

 number of trees within each type in conjunction with 

 volume tables based on taper measurements of large 

 numbers of trees. The base diameters of these sound 



40 Chains 



normal trees are tallied as measurements, giving an im- 

 personal volume control of the sound timber. Allow- 

 ances for abnormal form and visible defect are tallied 

 by trees as opinions. Allowances for unseen defect, 

 breakage in falling, and other shortages, are made by 

 types, or other subdivisions, rather than by trees. 



The form in which the results of a cruise, or forest 

 survey are presented, is an important consideration. A 

 topographic map, with contours, and timber types dis- 

 tinctly outlined is most essential. This furnishes a bird's- 

 eye-view of all conditions of interest to an owner, opera- 

 tor or prospective purchaser. The cruise figures may be 

 put directly on the map, or tabulated separately by units 

 of area. A separate cruise sheet or sheets furnish a com- 

 pact summary of kinds, quantities, and sizes of timber. 

 A written report covers all points not graphically shown 



on the maps and cruise 



Cruise Line 



\ 



PLAN SHOWING ARRANGEMENT OF CRUISE LINES ON QUARTER 

 SECTION 1 Kill ACRES) 



The dash lines represent the cruiser's line of travel. The light solid 

 lines on either side of the dash lines are boundaries of the strip within 

 which all trees are tallied. The topographic features between cruise 

 lines are mapped as far as can be seen on the line of travel, thus filling 

 in from line to line. 



and how much better or 



sheets, including a discus- 

 sion of logging conditions, 

 markets, etc. The whole is 

 calculated to give the fol- 

 lowing results : 



1. A reliable basis for 

 valuation. 



2. A basis for an effec- 

 tive plan of operation. 



3. The best possible 

 location of roads, camps 

 and other improvements. 



4. A reduction in loss 

 from windfalls and normal 

 decay. The felling areas 

 can be adjusted with refer- 

 ence to the need of prompt- 

 ly cutting damaged or over- 

 mature timber. 



5. The preservation of 

 knowledge relating to the 

 property. Without a sur- 

 vey system, much informa- 

 tion may depart with those 

 who happen to possess it. 



6. Reduction in loss in- 

 change of management in an operating 

 An adequate forest survey provides a new 



cident to 

 company. 



manager with a mass of essential knowledge ready for 

 his use. 



7. Efficiency of fire protection system. 



The cost is not the least important point in connection 

 with forest surveys and cruising, though it has been left 

 until the last. The charge for a complete showing as 

 outlined above, rarely exceeds two cents per thousand 

 feet, and usually is nearer one cent. 



A CHRISTMAS SUGGESTION 



Are you puzzled about the selection of Christmas gifts? 



Why not give a year's subscribing membership in the American Forestry Association as a gift. It will cost 

 you $3.00, and the member will receive American Forestry Magazine for a year. 

 This will be an ideal Christmas gift for a child or an adult. 

 Send the money to the Association and a Christmas Card will be sent you to present on Christmas Day. 



