, 



Fig. 8. After 10 years, rows 3 and 7 are cut from the shelterbelt and replanted. 



Fig. 9. After 15 years, the remainder of the' old planting, rows 4, 5 and 6, are 

 cut out and replanted. 



456 



Fig. 10. After 20 years the youngest trees, in the interior of the grove, rows 

 i, 5 and 6, are 5 years old and the oldest, rows 1 and 9, are 20 years old. 



