THE THEORY AND PRACTICE OF WORKING PLANS 65 



might be termed the ' pathological rotation.' " The species in 

 mixed stands can usually be worked on the same rotation unless 

 they mature at different ages or are markedly different in 

 value, e.g., a mixed forest of Engelmann spruce and white fir 

 {A. concolor) will often require a higher rotation for the spruce 

 than for the fir; because the fir deteriorates at an earlier age 

 and becomes almost valueless at a time when the spruce is just 

 fully matured. 



Where the species are not intermingled but form pure groups 

 or stands in the same working group, the rotation is determined 

 separately for each species comprising more than one-third of 

 the total volume, and the results are then averaged. 



Note. — In connection with rotations involving financial calculations, see chap- 

 ter in Roth: " Forest Valuation," on " Relation of Capital and Income in 

 Forestry," pp. 73-82; also, Chapter VIII, pp. loo-ng in Chapman: "Forest 

 Valuation." 



