Survival and growth ofPicea glaucaseedlings as a function of freezing temperatures and exposure times during budbreak and shoot elongation

The impact of freezing temperatures and exposure times during budbreak and shoot elongation on 10-month-old containerized white spruce seedlings [Picea glauca (Moench) Voss] was studied. Seedlings were exposed to 0, −2, −4, −6, −8 and −10°C for 0, 1, 2, 3, 4, 5 and 6 h at four stages of budbreak and shoot elongation (stage 1: unswollen bud; stage 2: swollen bud; stage 3: bud scales parted by emerging needles; stage 4: 1–5 cm of terminal shoot growth). Seedling and terminal bud survival, viability of first-year needles (developed before frost exposure), terminal shoot length, stem diameter and aerial dry mass were measured 90 days after freezing exposure. Frost severity had a much greater influence on seedling survival, damage and subsequent growth than exposure time. The bud development stage at which freezing temperatures were applied also affected survival and subsequent growth.