16 



associated Conifers such as Araucaria Cunninghami, A. Bldwilli and Damnmra robusta, 

 do not grow fast enough for mixed culture. 



PRODUCTION OF WOOD. In the case of Gums, the rate of growth may he ascertained 

 accurately, as there are sufficiently old plantations of the kind in Natal. Mr. Topham's 

 plantations near Maritzburg may be taken to be a fairly average one. The oldest plot, 40 

 acres in area, is 17 years old and consists of mixed Eucalyptus globulus, E. longifolia and 

 E. rostrata, the rate of growth of each appearing not to differ widely. The trees are 

 planted 12 feet apart, so that there are 302 to the acre ; they average 4 feet 10 inches in 

 girth at three feet from the ground, and 115 feet in height. Adopting the form factor 

 of 0'450, deduced from Mr. D. E. Hutchins from measurements in plantations on the 

 Nilgiris*, the contents of each tree average 96'3 cubic feet and the standing stock per 

 acre 29,083 cubic feet, representing a yearly increment of 1,711 cubic feet per acre. The 

 weight of a cubic foot of E. globulus (dry wood with bark) averages 40 Ibs., equal to 56 

 cubic feet per ton, according to Mr. Hutchins, and the average density of the wood of the 

 other species differs so little that it may be taken as being the same. The annual 

 increment in tons of dry wood per acre is thus 30*5 tons, and this is a marvellous rate of 

 growth. Individual trees even greatly exceed this rate, one specimen of the E. longifolia, 

 17 years old, being 12 feet 6 inches in girth at three feet from the ground, and 115 feet 

 in height. In India, the rate of growth of E. globulus averages in seven plantations on 

 the Nilgiris 1T24 tons of dry wood per acre, per year. 



We may take a yearly acre increment of 1,000 cubic feet to represent the average 

 growth, in Natal, of the faster growing Gums. This growth corresponds to an increase 

 in diameter of about an inch a year, when the trees are planted 12 feet apart, a rate 

 which is exceeded at Howick and elsewhere. 



Data respecting the growth of Pinus insignis are insufficient to make it possible to 

 form a conclusion as to the average rate of growth. Individual trees, partially isolated, 

 grow at Howick at the average rate of nearly 6 inches in girth a year, attaining a height 

 of 45 feet in 10 to 12 years. 



MONEY RETURNS. From a financial point of view, a forest or plantation may be 

 regarded as capital returning an annual yield of wood, in the same way that a sum of 

 money produces interest. The highest return is secured by adopting the rotation which 

 gives a highest prospective value to the forest, this consisting of the present value of all 

 sums receivable in the future, less the present value of all sums expended or to be 

 expended. 



Taking the case of a plantation of mixed Gums, 2,500 acres in extent, and adopting 

 for the calculation of present value, a rate of interest of three and a half per cent., which 

 is the current cost, to Government, of money borrowed, the outlay will consist of the 

 sum of : 



* D. E. Hutchins, Report on measurements of the growth of Australian trees on the Nilgiris, Madras, 

 1883, p. 15. 



