46 PURE AND MIXED WOODS 



latter are left so far apart that they grow short and branchy. 

 If, on the other hand, the conifers are left standing too long, 

 the oaks are suppressed and the wood becomes practically 

 a coniferous one, the so-called permanent crop being ruined. 

 It is better to do without nurses. When oak is planted pure 

 and dense, each tree nurses its neighbour, and if the wood 

 is underplanted with beech, a far better crop is eventually ob- 

 tained than under the system of planting with conifer nurses. 



Although mixed woods are recommended wherever the 

 area is extensive, yet pure woods are quite admissible under 

 certain circumstances, more especially if the species is a soil 

 improver ; thus pure woods of beech, hornbeam, spruce, silver 

 fir, and Douglas fir may be -grown if desired, though the 

 conifers are more likely to suffer from insect and fungoid 

 attacks. Coniferous woods are often found pure in nature, but 

 in such places the soil and climate are usually thoroughly 

 suited to them and they therefore do not suffer so much from 

 insects and fungi as they do when artificially grown pure 

 in less favourable spots, and if we plant them pure, we must 

 understand that a risk is taken. 



Scotch, Weymouth, Austrian and Corsican pines, and sweet 

 chestnut are capable of preserving the fertility of the soil up 

 to thirty or forty years and may therefore be grown pure, 

 provided they are to be cut at this age to provide pit-wood or 

 other small produce. 



Other cases where pure woods are allowable are, when the 

 soil is obviously suited for one species only, e. g. Scotch pine 

 on poor, dry, sandy soils; or when only one species is saleable 

 at present, and when it is unlikely that other species will be 

 saleable in the future. 



Ash, elm, maple, sycamore, poplars, and tree willows are 

 never found in large masses in natural woods, and they do not 

 flourish in artificially formed pure woods. They should, there- 

 fore, always be scattered here and there in small groups in 

 woods consisting chiefly of other species. 



