Methods 



Artificial defoliation was studied in a 5-year-old white 

 pine plantation at the Memorial and Mohican State Forests in 

 Ohio in 1960 and 1961. Sixty healthy white pines were ran- 

 domly selected from trees growing on similar sites. Four dif- 

 ferent treatments were compared: complete defoliation, re- 

 moval of current needles only (those that grew out in 1960), 

 removal of all foliage except current needles, and no defolia- 

 tion. One-third of the 60 trees were treated in July 1960 

 during the growing season, one-third in late September 1960 

 during the dormant season, and one-third in April 1961 before 

 candle elongation. Five trees received a particular treat- 

 ment each time. 



Growth in 1960 was compared with growth in 1961, height 

 of each tree and annual growth of four of its shoots being 

 measured. Both tree height and shoot growth were analyzed 

 statistically to establish significance of response to all 

 treatments. Radial growth was not measured because it is 

 difficult to accurately record in young trees. Vigor and 

 survival were taken into account in final records. 



Results 



In some cases all five of a group of treated pines died 

 and it was not possible to compare growth before and after 

 defoliation. But number of defoliated pines killed gave some 

 idea of importance of the particular needles removed and the 

 effect of time of defoliation. Complete defoliation killed 

 all five trees so treated in July and all five so treated in 

 April. But it killed only three white pines out of the five 

 so treated in September. When carried out in April, removal 

 of current needles also killed trees, only one white pine out 

 of five treated at that time surviving. But when current 

 needles were removed in July and September, all trees sur- 

 vived. When current needles were retained but all others re- 

 moved, all trees survived, regardless of season of defolia- 

 tion. 



Growth and vigor of trees surviving were more influenced 

 by age of needles removed than by season of defoliation. The 

 two trees that survived complete defoliation displayed 

 chlorotic dwarf-like symptoms of shortened internodes and 

 chlorotic needles (figs. 1 and 2). Their shoot growth was 

 greatly reduced (table 1). 



