352 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. 



