THE DOUGLAS FIR IN SCOTLAND. 



235 



The following extract shows the mean volume of solid wood in 

 a well-stocked silver fir wood growing in a locality classed as 

 belonging to the first quality up to an age of 140 years, beyond 

 which asre no figures are available : — • 



In order to prepare a similar table for Douglas fir, it is necessary 

 to ascertain the total sectional area per acre, the mean height, and 

 the form figures for the years 50, 75, 100, 125, and 140 ; 

 and this, with the scanty material at present available, can only be 

 done in a rough and preliminary manner. 



Sectional Area. — We know that the sectional area of a dominant 

 (or leading) tree is as follows : — 



In order to ascertain the total sectional area per acre at these 

 periods, we must ascertain the number of trees which a well-stocked 

 acre is likely to contain at the same periods. We know (1.) that a 

 ■well-stocked acre contains 202 Douglas firs at the age of thirty-two 

 years; (2.) that 101 silver firs 140 years old, of a mean sectional 

 area of 3-495 square feet, find room on an acre ; (3.) that generally 

 a Douglas fir requires at least as much room as a silver fir of the 

 same sectional area, and, in fact, somewhat more, owing to the 

 somewhat more spreading nature of the branches ; and (4.) that a 

 Douglas fir 140 years old shows a sectional area of 4-307 square 

 feet. 



