FIELD PERFORMANCE OF CONTAINERIZED BLACK SPRUCE SEEDLINGS WITH ROOT SYSTEMS DAMAGED BY FREEZING OR PRUNING

Roots of 2-year-old black spruce seedlings (Picea mariana [Mill.] B.S. P.) were exposed to freezing temperatures to destroy 20, 40, 60, and 8 0% of the root systems. For comparison, other root systems were pruned to eliminate the same proportions of roots. Treated and control seedl ings were planted in spring 1992 at Foret Montmorency (the Universite Laval forest research station, 50 km north of Quebec City). From 1992 to 1995, survival, shoot height and stem diameter were measured. Morta lity mainly occurred in 1993, the year after planting; pruned seedling s showed practically no mortality while seedlings with 20, 40, 60, and 80% of their root systems affected by frost showed mortality rates of 0, 6, 17, and 24%, respectively. Shoot height and stem diameter decre ased with increasing root damage when compared to controls. After thre e years on the planting site, shoot height was reduced by 2, 8, 11, an d 18% while stem diameter was reduced by 4, 21, 25, and 24% for 20, 40 , 60, and 80% frost damage, respectively. For pruned seedlings, shoot height was increased by 3% at 20% damage and was decreased by 1, 3, an d 13% for 40, 60, and 80% root damage while stem diameter was reduced by 1, 4, 8, 19% for 20, 40, 60, and 80% respectively. Use of damaged s eedlings on the planting sites should be limited in order to reduce th e cost of replacement planting.