TREES FOR WATER CATCHMENT AREAS 159 
As a main crop it is ripe for felling at 60 years old; and 
coppice of it is cut every 15 years. 
Chestnut has a very limited use in afforestation, as it 
can only be grown commercially in favoured spots. It can 
rarely be planted in the hills; and is quite unsuitable for 
low damp places or for situations that are exposed to wind. 
Chestnut bears shade when young; but after 30 years 
requires much light and space. It may, however, be grown 
as a pure crop on suitable sites ; but the stems stand far apart, 
scarcely exceeding 60 to 100 per acre on good soil at 60 years 
old. It is suitable for mixture with ash or larch, if the soil 
suits these species. In such mixtures, the chestnut can be 
cut over and kept as coppice, amongst which the ash and 
larch will grow well as standards. In other cases, the larch 
may be removed as thinnings, and the chestnut allowed to 
remain. In Quarterly Journal of Forestry, vi. 20 (1912), 
there is a description of a very successful plantation of 
larch and chestnut on heavy loam in Gloucestershire; the 
trees were planted 6 feet apart, the two species being in 
alternate rows. 
Elm.—None of the species of elm as a rule form pure 
woods, but are almost invariably in the wild state scattered 
singly or in small groups in the broad-leaved forests. Of 
the various species in this country, practically only the 
wych elm is found naturally in woods. The other kinds 
are seen in hedgerows, parks, or avenues; and if, as is 
probable, they also are native, the original forests in which 
they grew have long since disappeared, giving place to farm 
land. All the elms bear shade in youth, but later they re- 
quire considerable light and space. They need a soil of 
at least moderate fertility and depth, and there must be 
sufficient moisture. Elms are quite unsuitable for very dry 
soils, such as dry sand, stiff clay, or thin chalk. The 
various elms have marked differences in their climatic re- 
quirements, which will be pointed out in the following brief 
account of each species. None, however, ascend to a great 
elevation, and elms are not grown above the agrarian zone. 
