Timber Production and Groivth Curves. 3 



-conditions, thickness of planting, etc. It is evidently before the 

 50th year and after the 40th year. The curve rises somewhat 

 sharply from the 30th to the 40th year, and falls from the 50th to 

 the 60th, so that the maximum groAvth occurs between the 40th and 

 50th years. This is in accordance with the view that has been put 

 forward from time to time. But although the tree reaches maturity, 

 say, at its 50th year, it would not be correct to say that the tree is 

 then fit for milling. The sap-wood is about 1 inch thick, and this 

 represents so much waste. Further, the value of the wood produced 

 in the next decade, that is, from the 50th to 60th year, may still 

 give a good return on the money invested. But there is the further 

 advantage in leaving the tree to grow on for a further period. 

 Although the tree may have reached its maximum growth period, yet 

 it cannot be deduced that the wood has reached its maturity; for it 

 is quite probable that this wood will improve in quality during the 

 next twenty years. From observations of the logs coming into the 

 mill, it may safely be concluded that the tree at 80 years is still in 

 health, and therefore there need be no fear of heart rot. 



In Fig. 4 is given the total area of cross section during each 

 decade. There is a gradual rise of the curve, indicating a gradual 

 increase in diameter; but as in the other figs, we get a gradual 

 flattening of the curve after we pass the 70th year. This flattening 

 of the curve would indicate that the tree is losing its vitality, and is 

 hence open to attacks of all kinds. This is borne out by a study of 

 the standing forest, for tliere is a very intimate connection between 

 the paucity of foliage on these old trees, and the small amount of 

 wood produced in the older years. 



From the study of the annual rings, then, we may conclude at 

 present that the Mountain Ash reaches its maturity l^etween the 

 40th and 50th years; but we are not entitled to conclude that the 

 tree is then fit for milling. In view of the fact that in the future 

 a large proportion of this timber will probably find its way on to 

 t?ie market in a dressed and seasoned condition, the tree cannot be 

 said to be fit for milling until the Avood is ripe. It may well be, that 

 so long as the tree maintains a good head, i-he timber is improving in 

 quality, and therefore it m.ay be inadvisable to cut it during this 

 period. There are other factors as well to be considered with regard 

 to the time of harvesting the timber. The upkeep of this forest ig 

 small, at present, as compared with that of the forests of the old 

 world. Hence interest charges will be much smaller, and we could 

 therefore allow the forest to stand for a longer period than is the' 

 ■case with old world forests. 



2a 



