TREES FOR WATER CATCHMENT AREAS 155 
in height growth and gets above the frost zone. Alder has 
one great advantage in that it is scarcely ever attacked by 
rabbits, and may be planted without the expense of wire 
netting. It has been found useful in planting pit-mounds, 
slag-heaps, etc.; and this illustrates the fact that alder, while 
most successful in wet soils, is not confined to that situation, 
as it grows even in chalk. 
The wood of alder is at the present time of little im- 
portance ; but it is still used for making clog-soles, backs of 
brushes, mop and rake handles, inferior cigar boxes, hat blocks, 
etc. Itis very durable under water, and may be used for piles. 
Grey Alder.—The grey or white alder (Alnus incana) 
is not a native of Britain, but is widely spread on the 
continent, attaining its largest size, about 70 feet in height, 
in Sweden. It is considerably hardier than the common 
alder, and is remarkable for its vigorous growth in youth 
and its indifference to the nature of the soil. It grows 
on gravel and on cold clay, and flourishes in the frostiest 
localities. It is used in the Swiss Alps for preliminary 
planting in difficult situations at high altitudes, where as 
soon as it has formed canopy, it is underplanted with beech 
or silver fir, which are destined to be the final crop. It 
may be used for a similar purpose in this country, especi- 
ally for killing grass in low-lying frosty situations. When 
this is effected, the grey alder may be heavily thinned, and 
common spruce or Sitka spruce be planted under the 
protection of the trees that are left. Grey alder can 
also be used in planting pit-mounds, gravelly borders of 
streams, disused quarries, etc. As a permanent crop, it is 
best treated as coppice on a long rotation, of about 
30 years. Grey alder has been used with great success 
in the planting of pit-mounds in Belgium and France, but 
has not done quite so well as the common alder on the 
mounds in Staffordshire. Here it is, however, making good 
fertilising nodules on its roots, and is expected ultimately 
to thrive well. See Martineau, in British Association Report, 
Newcastle-on-Tyne, 1916, p. 494. 
