FOREST PER CENT 77 



per cent drops below 3% or whatever per cent may reasonably be 

 demanded by the owner, the stand is no longer worth holding. 



While the calculation is quite simple the actual determination 

 in the woods is not easy and is never more than an estimate rein- 

 forced by measuring the outer rings of a few trees. 



From these measurements the Pv or growth in volume in per 

 cent is determined by Schneider's formula; the per cent growth in 

 quality is estimated on a basis of diameter at beginning and end of 

 the period, and the per cent increase in market price is a figure 

 worked out for several years in any given district. Having this, the 

 growth of the stand is expressed in per cent for the three lines and 

 Pressler conceived the idea of simply using these as follows : assum- 



Ym 

 ing the actual growth in value per year is: (Fv -f Pq + Ps) 



100 

 and that this growth is made on a capital Ym + Se. 



TU / . , ^ Ym (100') , , . . ""■ 



Then pr =(pv -j- p, -.|-p.) — . „„, =(pv + p, -f-pO 



and 



To illustrate : If the stand is worth $250 and land $10 per acre 

 p» =1.3% 



Pa=I 

 ps=:l 



then pt = (1.3 +1+1)^^^^ or 3.1%. 



Since this method or inquiry is usually applied only to older 

 stands where the value of the timber is very large as compared with 



Y„ 

 the value of the land, the value of may be put = i and for 



Y„+Se 



ordinary purposes, therfore, it is quite sufficient to state : 



Pf =Py + Pa + Ps ; in the above case Pt = 1.3 + i + i = 3-3%, a 



very convenient form. 



In the United States where at present the value of timber is 

 usually by M. ft. b.m. on rather uniform price per M. feet, the case 

 of working out the data for p; may take the following form : 



Assume stand of pine, pure, even aged, 80 years old; volume 

 table exists for species and district ; from borings or felling the 

 diameter growth of the timber is ascertained, the stand is calipered 



