1 66 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



The mean annual increment is obtained by dividing the 

 estimated growing crop for any particular year by the number 

 of years which have elapsed since planting. The current 

 annual increment is obtained by applying the percentage rate 

 of growth to the estimated growing crop of that year. No 

 account has been taken of intermediate thinnings of which no 

 records exist. 



The Japanese larch have been placed first although the 

 observations only cover five years, owing to the remarkable 

 nature of the results obtained. The trees are growing on a 

 bank at about 300 feet elevation with south-east aspect. It will 

 be observed that the crop had become measurable within eight 

 years from planting, and that the current annual increment 

 for 1917 was 183 cubic feet per acre, without any sign of 

 diminution. The percentage rate of growth is also very high. 

 It is scarcely to be expected that growth can continue very 

 long at this rate, and in view of the widely held opinion that 

 Japanese larch ceases to make satisfactory growth at a 

 comparatively early age, it will be interesting to see how far 

 this view is supported by actual observation. It is doubtful 

 whether any other species, unless Douglas fir, can show a 

 correspondingly rapid rate of growth. 



The spruce in Plantation D are growing on good soil but the 

 crop is rather thin, and has been dominated to some extent by 

 scattered hardwood trees. These conditions are reflected in the 

 comparatively poor mean annual increment. It is only in 

 recent years that the crop has begun to escape from these 

 conditions, and the current annual increment has now reached 

 the fairly good figure of 113 cubic feet per acre per annum. 

 In this as in other cases it will be observed that a falling 

 percentage rate of growth does not necessarily mean a falling off 

 in the total increment per acre, for the reason that the percentage 

 is each year calculated upon a larger total quantity. 



The spruce in Plantation B represents a different class of soil 

 and situation, the crop being grown upon what was formerly 

 hill land not previously under trees. The results are on the 

 whole favourable, the current annual increment remaining still 

 fairly constant at over 100 cubic feet per acre per annum. 



The spruce in Plantation K also represents a crop growing 

 on what was formerly hill pasture. The soil in this case is 

 somewhat poorer, and the current annual increment shows signs 



