Part II. ] 
Caccia : Development of Sal. 
201 
from that of a single tree both as regards increment in height and dia- 
meter, basal area and volume ; and it is impossible to deduce the pro- 
gress of the volume increment of a whole wood from that of a single tree 
in the crop. In a whole wood, in the struggle for existence, the least 
vigorous stems disappear : what is now the mean tree of a crop must 
formerly have been a dominant tree. Consequently both the mean 
height and the mean diameter of a crop increases more quickly than that 
of the individual trees. Again, when a tree passes into the “Minor 
Part ”of the wood (intermediate class), the basal area and the volume of 
the Principal or “Major Pari ” of wood is reduced by that amount. 
Consequently the total or Final Yield of a whole wood at any given age 
is equal to the volume of the wood at that age plus all intermediate 
yields previously exploited. 
The collection of data relating to the development of whole woods is 
of the greatest practical utility to the forester, since it leads to the pre- 
paration of Yield Tables, which are indispensable in the systematic work- 
ing of forests, besides indicating, sufficiently accurately, the normal 
growing stock corresponding to a given quality of locality and rotation. 
Yield Tables may either be prepared for a particular district of limited 
extent, or for a whole province or country : but local Yield Tables are 
undoubtedly to be preferred. The Forest Research Bureaux of Europe 
have agreed to show in each Yield Table the development of normal 
woods of five different quality classes, namely : — 
Class I.— Best Quality Locality. 
,, II. Qood ,, ,, 
,, III. — Medium ,, ,, 
„ IV. — Mediocre,, ,, 
,, V. — Inferior „ „ 
The quality class to which a wood belongs is indicated by its cubic 
contents at the age of 100 years.* Thus a normal Scotch Pine wood, 
100 years of age, yielding a volume of 7,500 cubic feet per acre or over 
would belong to the first class ; one yielding 6,000 cubic feet per acre 
falls into the second class ; and so on. 
In making use of Yield Tables considerable difficulty is sometimes 
experienced in determining the quality class to which a particular wood, 
whose future development it may be required to ascertain, belongs. 
Considerable divergence of opinion exists as to the particular index to be 
accepted ; the locality (soil and climate), the height growth, the diameter 
increment, the basal area, and the volume of the wood have each been 
*Accordiiig to the decision accepted by the Forest Research Rureaux of Germany at 
a Forest Conference held at Ulm in 1888. 
