REVIEWS AND NOTICES OF BOOKS. 89 



Methods of ascertaining the increment in pure, even-aged 

 forests, in uneven-aged, and in mixed forests are treated by the 

 authors very comprehensively. In pure, even-aged forests, the 

 type of forest most frequently used for investigations of this 

 kind in Britain, the following is an outline of the procedure 

 advocated : — 



"The increment in pure, even-aged forests, is best studied by 

 laying out a large number of plots and measuring the 

 trees thereon. From these measurements, yield-tables 

 are constructed from which the increment can be obtained. 

 If, in the selection of the stands, wide ranges in age 

 and quality of site have been observed, maximum and 

 minimum curves can be drawn, and, depending on the 

 large number of site qualities to be recognised, inter- 

 mediate curves can be interpolated which will harmonise 

 with the maximum and minimum curves, and also make 

 the breadth of bands equal for any given age." 



Three chapters, xii. to xv., are devoted to the subject of 

 Forest Organisation, that branch of the subject which concerns 

 itself with the organisation of a forest property for management 

 and its maintenance, ordering in time and place the most 

 advantageous use of the property with the ultimate aim of 

 securing the sustained yield. The normal forest is a standard 

 with which to compare an actual forest in bringing out its 

 deficiencies for sustained yield-management ; the conception of 

 an ideally regulated or organised forest. The term "normal" 

 is used in the sense of conforming to a standard rule or principle 

 — a model. Such a forest does not actually exist. 



The normal growing stock may be obtained (i) from yield- 

 tables ; (2) by formula. In the determination of N V from yield- 

 tables constructed by measurements of fully stocked stands, the 



formula used is: — NV = N( a -t-(^-|-r-F ...-'] where N = number 



of years separating each age-class (step of the yield-tables, 

 say ten years), and a, b, c,...?n volume per acre given in the 

 table for each age-class. 



N V may also be expressed by the formula — N V = — 



2 



where r = rotation, / = mean annual increment, or more 



correctly by the formula NV = <:/-/ where c, a constant, is first 



