EFFECT OF THE DHOLiTH ON FOREST TREES 227 



OTHER EFFECTS OF DROUTH. 



While an excess of water in compact soils, as are found in portions 

 of the irrigated sections of Nebraska, becomes injurious through impeded 

 aeration of the tree roots, this trouble being made apparent in the pallor 

 of the leaves, a deficiency of water in a season of drouth produces similar 

 premature pallor or yellowing of the leaf. This is apparent mostly in 

 single or individual branches, and records the fact that nearly formed 

 rootlets supplying that branch with soil moisture have been killed by 

 the drying out of the soil. A shortening of the year's growth and the 

 drying out of the portions of the bark, as described in reference to the 

 white pine, are other results of the shortage of soil moisture. » 



Foresters call a dead topped tree a "stag headed" tree. The 

 most common cause for a stag headed tree is dearth of soil moisture , 

 at the roots. The lower branches may obtain sufficient nourishment to 

 maintain a normal appearance, yet with shortened growth, and with con- 

 tinued drouthy soil conditions the creeping paralysis of stag headedness 

 creeps annually downward until the tree completely succumbs. 



Drouthy conditions at the root may be independent, however, of 

 drouthy atmospheric conditions. The roots may be in too moist soil and 

 the physiological effect upon the tree may be the same as that of too 

 little moisture; the moisture may not be available to the tree, because of 

 the presence of humic acids from the decay of humus in the water. 

 These acids may induce an "outward" flow from the rootlets rather than 

 the necessary "inward flow," just as alkali in solution in soil water 

 causes an "outward" flow from the rootlets. 



PRACTICAL APPLICATIONS. 



While we can not alter the climatic conditions and can not prevent 

 drouths, we can to certain extent mitigate their consequences. 



1. We can use tree stock that has been grown from seed in this 

 climate, and, if possible, from seed obtained from trees grown here. 



2. We can choose species adapted to rigorous climates, especially to 

 those in which drouthy conditons are not uncommon. 



3. When planting young trees we can select specimens with well- 

 developed root system, such as is obtained from transplants. 



4. If not using home-grown tree stock or trees native to the state, 

 we can use stock grown in as arid or more arid situations, or use trees 

 adapted to even more drouthy conditions than prevail here. This, how- 

 ever, can be overdone, as, for instance, the drouth-enduring western yel- 

 low pine will not thrive in the moister parts of Nebraska. 



5. Just as through cultivation and the preparation of a finely 

 pulverized soil mulch mitigates drouth in agriculture, the same soil treat- 

 ment is beneficial with trees. If the trees are in young plantations, cul- 

 tivation can be carried on in a manner similar to the treatment of the 

 corn crop. With larger trees in a wood lot this, of course, becomes im- 

 practicable, but with lawn and street trees a deep spading, following with 

 raking finely the surface, will do much to help the tree through the crisis. 



