32 



ILLINOIS NATURAL HISTORY SURVEY CIRCULAR 51 



and proper installation of brace rods and cables may prolong the 

 life and improve the appearance of a tree. Trees which produce 

 brittle wood, or which have narrow, V-shaped crotches (Fig. 30), 

 such as honey locust, poplar, Siberian elm, soft maple, and wil- 

 low, are especially susceptible to breakage from wind and ice 

 storms. Such trees frequently need artificial support to overcome 

 their structural weaknesses or to correct for storm injury. Usu- 

 ally bracing and cabling is hazardous work and should be per- 

 formed by trained individuals who have the proper skill, mate- 

 rials, and equipment. 



Grade Changes 



Removing or adding soil around trees frequently causes 

 injury to roots. Excavating over 6 inches of soil usually injures 

 or destroys numerous fibrous roots through which trees obtain 

 water and nutrients (Fig. 31). Limiting the supply of water and 

 nutrients retards growth and causes branch dieback, general de- 

 cline, or death of the affected trees. 



Frequently trees can be maintained by building retaining 

 walls (Fig. 32) to avoid lowering the soil where most of the 

 fibrous roots are growing, although the adjacent grade may be 

 lowered considerably. If such corrective measures are not prac- 



Fig. 29 (Left).— Cabling 

 prevents branches or sec- 

 tions of trees from split- 

 ting or breaking. Such 

 protection is especially im- 

 portant during wind and 

 ice storms. 



Fig. 30 (Below).— Nar- 

 row, V-shaped crotches 

 (left) are weak because 

 the wood tissues are not 

 uniformly united and 

 patches of bark become 

 embedded in the tissues. 

 Crotches with wider angles 

 (right), called U-shaped 

 crotches, are strong. 



