REVIEWS 687 



by the followinor considerations : Although the height growth is so 

 similar in both countries that the same height curves could be derived, 

 it was found when the sample plots in each quality class were examined 

 that the data from the two countries could not be combined. In Scot- 

 land the number of trees, basal areas, and volumes per acre were con- 

 sistently higher than in England, though the remarkable fact appeared 

 that the relationship between quarter-girth and height was not af- 

 fected by this difference in stocking. No certain explanation can be 

 given as to the cause of this difference. 



It seems likely that in Britain the greatest practical utility of yield 

 fables at the present time is in connection with problems of replanting 

 and afforestation. On large areas suitable for planting operations 

 there are generally to be found a few scattered plantations of one or 

 more species, and by comparing their mean heights with the height 

 graphs some indication may be obtained as to the quality class of the 

 area for these species. When the quality of the locality has been de- 

 termined the tables can be applied in order to assess the probable pro- 

 duction, the rotation, and so on. As, however, they are prepared for 

 fully-stock areas it is necessary to employ a reducing factor to allow 

 for land not actually planted, such as rides, etc., for possible damage 

 by wind, fire, insects and fungi. The actual factor will depend upon 

 the nature of the area to which the figures are applied. 



The yield tables enable a comparison to be made of the rate at which 

 average woods of larch, spruce and Scots pine develop in Britain. In 

 the following extract from the tables the 60-foot classes of larch and 

 spruce are compared with the ."iO-foot class of Scots pine. These 

 classes are taken as representing an average rate of growth for the 

 respective species. 



It will be seen that in early youth larch grows fastest and spruce 

 slowest. This "hanging back" of spruce is typical of the species, and 

 is found in all qualities. In volume development, however, spruce 

 takes the lead at an early stage and maintains it throughout life. As 

 shown in the above table, spruce yields at 30 years of age 50 per cent 

 more volume of timber per acre than larch, and nearly double the vol- 

 ume of Scots pine. At 70 years of age the average spruce wood con- 

 tains one and three-quarter times the volume of the average larch 

 wood and one and a half times the volume of the average Scots pine 

 wood. Moreover, at this age every quality of spruce except the poor- 

 est carries a higher volume per acre than even the best qualities of 

 larch or Scots pine. 



