FOREST PLANTING IN THE EASTERN UNITED STATES. 17 



Another objection to pruning is the danger of overdoing it. If a 

 tree is pruned too far up it may become top heavy and be broken off 

 in a severe wind. Catalpa, ash, and black cherry are particularly 

 susceptible to injury in this way. The stems of young black cherry 

 and ash, when pruned far up, bend over by their own weight nearly 

 at right angles. Sucker sprouts then shoot up from the bent stems, 

 making a deformed tree. In a stand of black cherry 8 year,s old in 

 Indiana, where the trees were pruned to a whip, 11 per cent had been 

 broken off by the wind. 



Pruning also reduces the amount of leaf surface, the food-making 

 part of the tree, and hence reduces its rate of growth. 



Especially valuable species and trees with very persistent branches 

 should be trimmed at least of their dead breaches and sometimes of 

 their living ones. Of the species commonly planted, white pine, 

 black walnut, hardy catalpa, and black locust sometimes need 

 pruning. 



The lower branches of white pine are large and persist for many 

 years after dying. Sometimes, but not as a rule, it will be profitable 

 to prune the best trees in the stand by simply knocking off the limbs 

 with an axe after they are dead and have become brittle. Black 

 walnut seldom needs pruning, though occasionally dead branches 

 persist for a number of years which are likely to form loose knots 

 in the lumber. Such branches should be removed. Hardy catalpa 

 has very persistent branches, though the presence of knots in fence 

 posts, the chief product of catalpa plantations, scarcely impairs 

 their value. The dead branches are objectionable, however, because 

 they become loose and allow the entrance of wood-rotting fungi. 

 Since, therefore, these branches are a menace, they should be removed. 

 Catalpa, moreover, does not form a terminal bud, but ordinarily 

 develops three buds at each node. From those at the node nearest 

 the tip of the last year's shoot three new shoots arise, any one of 

 which may develop into a leader. In order to increase the devel- 

 opment of one of these shoots and thus control the tree's form, one 

 or both of the other two shoots on the node should be removed. 

 An effective and cheap way of doing this is to pinch off these shoots 

 just as they are developing from the buds. Black locust ordinarily 

 prunes itself readily, but when widely spaced the main stem often 

 forks into two or more main branches. In one young plantation 

 of black locust in Illinois, spaced 8 by 11 feet, fully 43 per cent of the 

 trees showed this fault. Such trees should if possible be pruned of 

 all but one of their leaders. 



The lower branches of Norway spruce are very persistent, but 

 not very large; hence for ordinary purposes the tree requires no 

 pruning. The ashes ordinarily prune themselves of their lower 

 60370°— Bull. 153—15 3 



