Root pruning, wrenching and overwinter cold storage : effects on the morphological and physiological condition of transplant Picea glauca [Moench] Voss nursery stock

Abstract

The objectives of this thesis were to; 1) evaluate the effect of a single early spring root pruning followed by a series of five root wrenching treatments at three week intervals on the morphological condition of rising 2+2 white spruce nursery stock, 2) to determine the effect of wrenching and several overwinter cold storage environments on bud dormancy progression, root regenerating potential and planting stock performance, 3) to assess wrenching as a method of conditioning bare root nursery stock for fall lifting and overwinter cold storage. Root pruning and wrenching was applied to rising 2+2 white spruce in nursery trials one in 1982 and another in 1983 at the Ontario Ministry of Natural Resources Forest Station, Thunder Bay Ontario. The root pruning and wrenching treatment reduced current height increment, reduced the number of primordia in the winter buds, and in 1983 significantly increased root area index. Root pruning and wrenching increased the overall root regenerating potential of stock during overwinter cold storage. Wrenching and root pruning did not significantly alter bud dormancy progression or patterns of root regeneration during the winter. Both the control and the root pruned and wrenched stock was overwinter cold stored in 3 storage environments. The progression of bud dormancy and root regeneration potential of this stock was monitored monthly for a seven month period during the winter. Stock that was fall lifted and overwinter stored had the same winter bud dormancy pattern as stock overwintered in the nursery bed but a different pattern of root regenerating potential. Cold storage delayed bud flushing in the spring and prevented frost damage from occuring after spring outplanting. A six week spring warm up conditioning treatment at +2 C in cold storage increased root regenerating potential. The exposure of fall lifted stock to natural photoperiods while overwintering in an unheated polyhouse did not appear to improve planting stock quality over that of the same stock overwintered at -2 C in complete darkness.