298 



The Thinning of Woods. 



earlier and more frequent assistance than shade-bearing 

 trees. 



Finally, soil and situation must also be taken into 

 account ; for on inferior soil, and on an exposed or otherwise 

 unfavourable situation, there exists a greater necessity for 

 shortening the natural struggle than on favourable soils 

 and situations, where the conflict between the stronger 

 and the less vigorous stems is shorter, sharper, and more 

 decisive. 



In thinning operations the dead and dying stems should 

 invariably be removed, as they are apt to form breeding 

 grounds for noxious insects and nidi for the propagation ot 

 fungous diseases. If confined to these, however, the operation 

 can only be considered a slight thinnmg. A moderate thin- 

 nmg removes also the suppressed class of stems, while a 

 heavy thinning eliminates the dominated stems in addition 

 thereto. Even in a heavy thinning the extent to which the 

 dominated stems should be removed depends in each case on 

 the concrete factors above referred to, the limitations of the 

 thinning being dependent on the energy of the growth in 

 height and on considerations regarding conservation of the 

 soil. From the age of 15-25 years onwards, pole-forests of 

 Oak, Ash, Larch, and Scots Pine should be thinned, if prac- 

 ticable, about once every five years ; while similar woods of 

 Spruce, Silver Fir, Beech, and Maple ought not to require the 

 operation till between the twentieth to thirtieth year, and 

 after that not more than once every eight or ten years.* The 

 best rule for thinnings is to begin them early, to conduct 

 them moderately, and to repeat them frequently, bearing in 

 mind that on inferior classes of soil the conservation of its 

 productive capacity demands that the thinnings should be 

 slighter, but more frequently repeated, than on good soil. 



* In Continental forestry the term thinning is applied only to operations in which 

 the value of the stems cut out cover, or more than cover, the cost of the operation. 

 Previous to that, the operations conducted on the same principles for the benefit of the 

 growing crop are called weedings and cleanings, " weedings " referring to the removal 

 of other kinds than the main crop, and " cleanings" to the elimination of weaklings or 

 superfluous portions of the latter. This is a purely arbitrary technical definition, which 

 indicates that charges for weeding and cleaning are debitable to the growing crop 

 while thinnings either cost nothing or else form a source of revenue, with which the 

 land and the crop must be credited. 



