TREES TO USE IN STARTING WOODLOTS 69 



height of the trees. Groves and sometimes forests are also 

 grown for protection from the wind. 



The influence of a windbreak is proportional to its height 

 and density. The influence is appreciable for a distance equal 

 to five times the height of the trees in the windward direction 

 and fifteen or twenty times the height to leeward. The dis- 

 tance increases with the velocity of the wind. 



Windbreaks have a somewhat damaging effect on crops, 

 due to the shade cast by the crowns of the trees, and also to 

 the sapping of the soil moisture by the roots. Species having 

 narrow crowns or light foliage and which do not extend their 

 roots far should be selected where the injury is likely to be 

 considerable. 



Sapping the soil moisture by the roots of trees can be over- 

 come in large measure by very deep plowing each year to cut 

 off surface roots of the trees. Cultivating the soil near the 

 trees will tend to induce them to secure their food closer to 

 the trunks. Tap-rooted species like white pine, Norway pine, 

 oaks, hickories and maples can be used. Green ash, osage 

 orange and mulberry do not extend their roots far. Often 

 the value of the timber and other products, as well as the 

 protection secured, will more than repay any loss from the 

 crops. 



The trees in windbreaks should be planted closely together 

 so that the branches will interlace and make an effective 

 shelter. The narrower the belt the closer the trees should be 

 planted. Trees with slender crowns can be planted closer than 

 those with wide-spreading crowns ; slow-growing trees closer 

 than fast-growing species. In general the trees should not be 

 planted farther than 5 or 6 feet apart. The rows are often 

 spaced 5 to 6 feet apart and the trees in the rows spaced much 

 closer together. 



In starting a windbreak the protection is desired as soon 

 as possible. To secure this a fast-growing tree should be 

 selected, even though it may not be a particularly desirable 



