60 



DEVELOPMENT OF FOREST TREES. 



moderately heavily thinned from their youth onward, hut this 

 interferes often seriously with the ([uality of the timber. 



Ajiart from these general considerations, a great difference 

 exists in the vohime produced by the several species when 

 grown in regular woods ; in this respect some of the more 

 important kinds may, according to the latest investigation, be 



l-'ir. 



Scotfh Pill.; 



AGE, IN YEAKS. 



Fig. 3. — Diii^iiiiii illustrating the rrodiiction of Titiiln- per Aiic, on Lociilitii.s ol 

 tlif First (iuality. l)y Spnuc, Beech, Scotch I'iuc, iiiul Silver Fir. 



arranged in the followhig manner, commencing with that 

 species which produces the greatest average increment, 

 ralcnliitcd for a proloiuicd .sjxicr of' time : — 



Douglas fir. 



Silver fir. 



Spruce. 



Weymouth pine, Larch. 



Jieech. 



