Effect of Cold Storage on Bud Break, Root Regeneration and Shoot Extension of Douglas Fir, Paper Birch and Green Ash

Abstract

Dormancy level, days to bud break, root regrowth and rate of shoot extension were determined for 18-in seedlings of Douglas fir ( Pseudotsuga menziesii (Mirb.) Franco), paper birch ( Betula papyrifera Marsh.) and green ash ( Fraxinus pennsylvanica Marsh.) subjected to varying durations of cold storage. Douglas fir seedlings did not break bud unless exposed to at least 4 weeks of cold storage, but bud break was unaffected by further time in cold storage. The number of regenerated roots increased with time in cold storage until 12 weeks of chilling and decreased sharply thereafter. Days to bud break of paper birch and green ash decreased as chilling time accumulated. Full dormancy release and maximum root regeneration of paper birch coincided at 10 weeks of chilling. Green ash achieved full dormancy release after 14 weeks of cold storage. The number of roots regenerated increased with cold storage duration for green ash. Shoot extension rate of all species was little affected by chilling duration. Implications for transplanting are discussed.