PURE AND MIXED WOODS 37 



a time, deteriorate. This must be prevented by growing the 

 light-demanders mixed with shade-bearing soil-improving 

 trees. In certain circumstances it is, however, legitimate to 

 plant the light-demanders pure, afterwards underplanting 

 with a shade-bearer. Such a wood is a mixed one for the 

 greater part of its life. 



4. By mixing different species together the damage done 

 by wind, fire, frost, insects, and fungi is usually reduced. 

 Thus, by mixing a deep-rooted species like Douglas fir with 

 a shallow-rooted one like spruce the danger from storms is 

 minimised ; an additional advantage of such a mixture is that 

 each species draws its nourishment from different layers of 

 the soil, which is, therefore, utilized to the fullest extent. 

 Conifers are less exposed to danger from fire when mixed 

 with broad-leaved trees. Frost-tender species like beech 

 escape damage by frost when planted under, or between, 

 hardy, light-foliaged species like oak or birch. Insects are 

 less dangerous in mixed woods as they usually attack only 

 one species, and the isolation of the stems and crowns by 

 other species retards the progress of the insect pest. Fungi, 

 like the larch disease, do less damage as the spores cannot 

 spread so easily, each tree being more or less isolated from 

 other trees of the same species. 



5. Mistakes made in the selection of species can be more 

 easily put right, as unsuitable species can be removed in the 

 thinnings without leaving the ground bare. 



6. The demands of the market may be better met from 

 mixed than from pure woods. If there is only one species in 

 a wood and the demand for that species, for some reason, is 

 reduced, there is nothing to sell except at a sacrifice. Too 

 much stress, however, should not be laid on this, as if one has 

 a large quantity of well-grown timber of any species one can 

 usually obtain a good price for it. 



7. Mixed woods are usually more beautiful than pure ones, 

 and are also better for sport. 



