TREES FOR WATER CATCHMENT AREAS 135 
namely, the Sitka spruce, Picea sitchensis, and the white 
spruce, Picea alba, both natives of North America. 
The common spruce is one of our most valuable trees, 
but its cultivation in this country has seldom been properly 
carried out. It has often been planted in unsuitable 
mixtures upon low-lying land; and when grown pure has 
almost invariably been over-thinned. Its real use is to 
produce a large volume of timber per acre in hilly or 
mountainous districts, as it makes good growth at altitudes 
where Scots pine and larch fail. In other words, spruce 
is the main tree for the afforestation of the higher parts of 
the hill pasture zone. Spruce is a superficially rooting 
species, and grows upon the thinnest soil, provided there is 
sufficient moisture available during the growing season. 
At high elevations, where exposure to the wind and little 
depth of soil are the chief obstacles to the growth of trees, 
spruce will produce a considerable volume of timber. 
Spruce can be raised and planted out with great ease 
and at a cheap rate, and it is a very hardy tree. It 
endures much shade, and when grown in close order covers 
the ground speedily, improves the soil by its layer of decay- 
ing leaves, and in due time cleans its stem, and produces 
timber of excellent quality. Used as a nurse for trees like 
larch and pine, its branches persist indefinitely, and coarse 
timber with large knots is the result. It should be planted 
pure as a rule, though in some cases, as on cold clay soil, it 
may be mixed with hornbeam or on dry soils with beech. 
As evidence of the considerable yield of spruce at high 
elevations, some statistics are available in Journal of Board 
of Agriculture, xvii. pp. 265 and 353 (1910), and Sup- 
plement No. 9 (1912). <A shelter belt on the summit 
of Kerry Hill in Wales, fully exposed at 1525 feet eleva- 
tion, the soil being four inches of peat on yellow loam, had 
a volume of timber of 2880 to 3160 cubic feet (quarter- 
girth measurement) per acre, corresponding to an annual 
increment of 70 to 75 cubic feet per acre. At 1400 feet 
elevation with less exposure, the soil being shallow loam, a 
plot 43 years old had a volume of 3870 cubic feet 
