27 



should be covered with paint or tar oil to prevent decay. Pruning 

 should be done in winter or early spring. 



THINNING. 



Thinnings consist in the removal of some of the trees in a grove in 

 order to give the remaining trees more room. The smaller and less- 

 promising trees are usually the ones cut. 



In many cases thinnings are necessary, since the trees removed can 

 be used for fuel, posts, stakes, etc., while the remaining trees are bene- 

 fited by the larger growing space. However, in this region of sun- 

 shine, with light- foliaged trees and rather wide spacing, thinnings 

 are of doubtful value, especially since most of the groves are to serve 

 as windbreaks. Farmers in renting their estates usually stipulate in 

 the agreement " that none but dead trees shall be cut." 



Occasionally dense willow groves in moist situations have been 

 thinned by their owners *with good results. Some of the river-bottom 

 groves furnish all the fuel consumed, as well as other material. Thus 

 the groves become a constant source of revenue in addition to their 

 value as a protection. In general, thinnings are advisable so long 

 as they do not make the growth of weeds and grasses possible. Grass 

 in a grove is always a detriment, and indicates that the leaf cover is 

 not dense enough. Light thinnings which interrupt the leaf canopy 

 only temporarily may be beneficial where a heavy thinning would be 

 positively harmful. Where thinnings are made a good rule is : " Be- 

 gin early, thin lightly, and repeat frequently." 



REGENERATING GROVES. 



In woodlots and shelter plantations permanence is especially de- 

 sirable. Whenever they begin to mature or deteriorate steps should 

 be taken to renew them. The trees planted in this region usually are 

 prolific seeders. All but willow and cottonwood are able to repro- 

 duce themselves to some extent under partial shade. Especially is 

 this true of boxelder and green ash. When trees of these species 

 grow close to cottonwood groves their seedlings often come up in 

 dense thickets as an understory. Russian mulberry, hackberry, red 

 cedar, and other species are occasionally introduced into a grove by 

 birds. However, instead of depending upon such chance or volun- 

 teer reproduction, or allowing grasses and weeds to grow it is ad- 

 visable to underplant. 



Underplanting is an operation which few have performed in the 

 past treatment of their groves. It is a very practical method of re- 

 newing them. Since a good many groves, particularly the older 



[Cir. 145] 



