FOREST EESEEVE MANUAL. 49 



and in board feet, of trees of any given- height and diameter. 

 The estimator should be able to approximate at a glance the 

 number of logs of any length in a tree, the average diameter 

 of these logs, and the number required to make 1,000 feet 

 B. M. Where the timber is to be used for sawed lumber, he 

 should note the probable proportion of the tree which will 

 furnish clear material. In all cases the probable percentage . 

 of cullf or decay should, at least, be approximated. Forest 

 officers should familiarize themselves with the condition of 

 each species within their district, and endeavor, by observa- 

 tions at mills and logging camps, to learn the average propor- 

 tion of unsound in each. Little timber will cull less than 10 

 per cent., and 30 to 40 per cent, is not uncommon in certain 

 species. The outward signs of defect, such as "conks," 

 "punk knots," exudations of resin, etc., should be carefully 

 studied. 



While officers, familiar with some particular methods of esti- 

 mating, may often do more accurate work by them than if they 

 attempt to learn entirely new systems, they should at least 

 acquaint themselves with as many as possible. Since for many 

 species of reserve timber the Government has prepared vol- 

 ume tables based on height and diameter at breast-high (4i feet 

 from ground), it is important to be able to estimate the latter 

 dimension readily. Given the number of trees of each diam- 

 eter upon a tract and a table showing the average contents in 

 board feet for these diameters, accurate computation of the 

 stand is simple. 



When these tables are not available, the breast-high diam- 

 eter may still be used by estimating the number of logs and 

 allowing a taper of about 1 inch in diameter to every 10 feet 

 in length. This taper varies slightly with the height and 

 species of timber, and the estimator should verify it by meas- 

 urements of fallen trees. 



Assuming, for illustration, that the estimator finds his tract 

 averages to the acre 25 14-inch trees, 13 16-inch trees, 14 

 18-inch trees, etc. ; also that all trees below 18 inches have an 

 average log length of 22 feet, and those above 18 inches a log 

 length of 26 feet, and, allowing a 2-foot stump and a taper of 1 

 inch to 8 feet, he finds that the average 14-inch tree contains 

 a 22-foot log Hi inches in diameter (outside bark) at the small 

 end. Or, if he wishes to reckon by smaller logs, it will make 

 4495—02 4 



