70 BRITISH FOREST TREES 



the axe is freely used. On the poorer qualities of soil 

 spruce never really ranks much higher than underwood, but 

 is even then of great advantage to the pine in maintaining 

 and stimulating the productive power of the soil, and in 

 hindering the formation of a rank growth of whortleberry or 

 heather. 



When older forests of Scots pine have an admixture 

 of spruce forming canopy along with them, they are 

 usually characterised by a good cylindrical form of bole 

 and large production of cubic contents per acre. They 

 also suffer far less than pure forests from various dangers, 

 and when the foliage of the pine has been stripped by the 

 caterpillars of swarms of moths, the spruce can often take its 

 place in the blanks formed, except when the ' Nun ' moth 

 (Liparis monacha) has been the cause, for then spruce is 

 usually much more injured than pine. In such mixed 

 forests breakage from snow is much less frequent than in 

 woods of pure Scots pine. Although in general advan- 

 tageous, there are however two cases in which an admixture 

 of spruce is not advisable ; namely, in the first instance, 

 on the better class of pine soils, where the pine is of deci- 

 dedly quicker growth than the spruce, and where the 

 interests of the proprietor are best served by growing the 

 pine pure and then later on under-planting with spruce, 

 and in the second instance, on the poorer classes of pine 

 soil where the spruce is unable to thrive. But on dry, im- 

 poverished mountain soil a mixture is often preferable, as 

 in pure forests the pine soon thins itself and does not pro- 

 tect the soil sufficiently, whilst the spruce has only a sickly 

 growth without any nurse. In such cases it depends on 

 circumstances whether the treatment to be accorded will 

 result in the mixed forest being pine with spruce, or spruce 

 with pine. Many of the present middle-aged mixed crops 

 of Scots pine and spruce in Germany arose from the 



