120 FORESTS, WOODS, AND TREES 
Extensive plantations of conifers are lable to wide- 
spreading attacks of fungi and insects, and to great damage 
from gales and fire. It is advisable, then, to interrupt the 
continuity of great areas of conifers by planting, at suitable 
distances, wide bands of broad-leaved trees. Beech is the 
most suitable species for this purpose ; but ash, sycamore, 
wych elm, alder, etc., may be added in varying proportions 
according to the nature of the soil. The influence of 
broad-leaved trees is manifold. Judiciously distributed in 
belts or in groups they act as wind-breaks; they are 
visited by birds which prey upon noxious insects; and the 
humus, due to their decaying leaves, brings health and 
vigour to the coniferous tracts. Broad-leaved trees may 
also be planted along the rides, rowan and grey alder being 
of use at high elevations. 
We are not limited in our choice of species to our few 
native trees. These are late immigrants from the Continent 
after the glacial epoch, and are by no means the trees that 
are most suitable to the climatic conditions of the present 
day, or that are most fit for producing, as quickly as 
possible, valuable timber. 
The Scots pine, our solitary native conifer of forest im- 
portance, was widely spread over the British Isles in the 
dry, warm, continental climate that prevailed at the begin- 
ning of the neolithic period ; but it has, with the advent of 
our present humid, cool climate, gradually disappeared from 
all parts of the country, except in the mountain massif of 
the Scottish Highlands. It is most suitable for districts 
characterised by a low annual rainfall and much sun in 
late summer and autumn, as in Speyside, Deeside, and Tay- 
side in the north, and in the sandy heaths of the south and 
east of England. In such districts it regenerates itself 
freely, and attains a great height, producing a satisfactory 
volume of timber of good quality. 
Fortunately we are not restricted to native trees. Dur- 
ing the eighteenth century, spruce, silver fir, and larch from 
the Continent began to be largely used in our plantations. 
The movement towards extensive use of exotic trees was 
