204 THE PRINCIPLES OF 'HANDLING WOODLANDS 



might be such a small density that intermediate or even 

 suppressed trees should be left to fill gaps. 



TOLERANCE OF SPECIES. Tolerant species suffer from 

 overcrowding less than intolerant species. To maintain 

 a full crown and rapid growth, the latter must be thinned 

 the more heavily. Conversely, to secure wood of high 

 quality, the stand must be kept denser with the tolerant 

 species. 



DANGER FROM WINDFALL. If there is danger from 

 windfall, the stand is thinned early and heavily in order 

 that there may be developed trees with strong roots. If 

 an older stand is dense, and there is danger from wind- 

 fall, the thinnings must be very moderate. 



SITE. On good soil the trees are vigorous and the 

 differentiation into crown-classes is more rapid and 

 sharply defined than on poor soils. The trees respond 

 quickly and energetically to thinnings, and fill very rap- 

 idly any gaps that have been made. Heavy thinnings 

 may be made on good soils without danger of exposing 

 the soil to drying influences. The poorer the soil, 

 usually the greater is the need of thinnings to secure 

 good growth, but the greater is also the danger of ex- 

 posing the soil. 



Time of First Thinning. The best results are ob- 

 tained if thinnings are begun early in the life of the 

 stand. It would be a benefit if light thinnings were made 

 as soon as the active crowding and sharp separation into 

 crown-classes begin. This would ordinarily be when 

 the trees are between 10 and 20 years old. In some 



