222 A MANUAL OF FORESTRY. 



with the more rapid development of the trees constituting 

 the final crop, leads to more favourable financial results. 



On the other hand, the early isolation of a portion of 

 the trees has weighty drawbacks. In the case of many 

 species it affects injuriously the height-growth of the 

 trees. Then, isolated trees maintain their side branches 

 low down, and even develop fresh ones, which seriously 

 reduce the value of the stems for many purposes. In 

 the case of conifers the quality of timber will also be 

 lower, owing to the formation of exceptionally broad 

 concentric rings. Isolated trees are further liable to 

 form more tapering boles than those grown in crowded 

 woods. Above all, in the majority of cases a sufficient 

 layer of humus and a suitable degree of moisture cannot 

 be preserved. It follows that, except on really fertile 

 soils, other means must be devised to preserve the con- 

 tinued activity of the soil. This is done by the intro- 

 duction of an underwood, or soil-protection wood. But 

 even then it is found that the extra increment, laid on 

 after isolating the trees, will only hold out on soils of 

 some quality, while on indifferent soils it will after some 

 years sink back to its previous amount. 



The general theory of the method of treatment in the 

 case under consideration may be shortly described as 

 follows : 



Commencing with the first thinnings, the most promising 

 trees are singled out, and these are isolated sufficiently 

 by increasingly heavy thinnings, so as to permit the 

 introduction of an underwood. As soon as the latter 

 has established itself, and is capable of protecting the 

 soil, a further heavy thinning is made, by which the 

 remaining trees are completely isolated. Subsequently 



