TREES FOR WATER CATCHMENT AREAS 131 
climatic requirements. It has not proved very successful 
as an isolated, ornamental tree in the milder parts of the 
British Isles, being prone to Chermes attacks, and often 
weakened by excessive production of cones. It is much 
more at home in the colder parts of Scotland, where it 
promises to be a valuable tree, as it is quite unhurt by the 
severest frost and is never injured by the heaviest snowfall. 
At Durris, Ardverikie, and Corrour, it is extremely hardy 
(Fig. 28) and resists wind better than any other conifer. 
Planted out on exposed sites, it has done well even on 
peaty soil. At Ardverikie it is the most vigorous of all 
the trees that have been planted there, enjoying immunity 
from fungus and insect attacks and producing natural 
seedlings in great abundance. Seedlings raised at Durris 
and Ardverikie from home-grown seed are very vigorous. 
It does not bear much shade, and fails where there is lime 
in the soil. In its own home it produces the most 
valuable timber of all the American silver firs, the wood 
being heavy, hard, and firm, and working easily and well. 
At Durris the wood is white and soft, but closer in the 
grain than that of Abies grandis. 
This species should be planted pure in the protection 
zone, when this is pushed high up in the heather moor. 
In this way in the west of Scotland it may be planted up 
to 1200 or 1300 feet, making a useful belt above the 
limit of the main-crop trees. It seems to be the most 
suitable species for use in an attempt to raise the timber- 
line on exposed sites on peat in the Highlands of Scotland 
and in the west of Ireland. Useful in this way at high 
altitudes it should never be planted at low elevations. At 
Craigo, near Montrose, not far from the coast at a low 
elevation a plantation of six acres of this species, 40 years 
old, shows only moderate growth, the trees ome about 
46 feet high by 4 feet in eirth, 
Douglas Fir.—This is perhaps the most valuable tree 
that has been introduced. It produces an enormous volume 
of excellent timber, and comes to maturity in a short term 
