852 ESSENTIALS OF BOTANY 
while to start large pieces of woodland by seeding or by 
transplanting young trees. The cheaper plan is to leave 
trees enough in the tracts cut over by the lumberman to 
re-seed the land and so keep up the covering of forest. 
But in treeless regions, as the prairies and the Great Plains, 
it is often a matter of much importance to secure belts of 
trees or considerable wooded areas (Sect. 423). This may 
be done by planting the seeds of the desired species in the 
places where the trees are to remain, or by setting out seed- 
ling trees procured from nurseries. The latter plan is 
much the more certain to insure success, as young trees 
that have been once or twice transplanted have no long 
roots and are not much checked in their growth by being 
set out where they are finally to grow. Coniferous and 
broad-leaved trees are freely planted on a large scale. 
Among the most desirable species of the former are sev- 
eral spruces, and the white pine, the Scotch pine, and the 
Austrian pine. Broad-leaved trees which are consider- 
ably planted, especially in the Central Plains region (e.g., 
Nebraska) are cottonwood, silver or white maple, green 
ash, honey locust, hardy catalpa, black walnut, eucalyptus, 
and red oak. 
423. Influence of Forests on Climate and Water Supply. 
— The effect which forests have on the temperature of the 
air and on the amount of rainfall in their neighborhood 
has not been fully determined. But it is well known that 
woodlands and even narrow belts of timber are of great 
service in winter by shutting off cold winds. For thus 
acting as wind-breaks coniferous evergreen woods are of 
course more effective than deciduous ones. ‘Tree belts 
have been largely planted in the more northerly prairie 
states for the protection which they afford. 
