TEMPORAL VARIATIONS IN THE ROOTING ABILITY OF CUTTINGS OF POPULUS-BALSAMIFERA AND SALIX-PLANIFOLIA FROM NATURAL CLONES POPULATIONS OF SUB-ARCTIC QUEBEC

Temporal variations in the rooting ability of cuttings from five clones of Populus balsamifera L. and five populations of Salix planifolia Pursh from the Great Whale River valley in subarctic Quebec were determined. Cuttings were sampled monthly from May through October and rooted in a greenhouse. Root number and length of the longest root per cutting were determined 35 days after planting. There were significant variations among the six sampling dates in the rooting potential of cuttings of both species. A higher percentage of cuttings formed adventitious roots in May and June before or shortly after bud break than later, during the growing season; root number and length followed a similar trend. There was an increase in the rooting ability of cuttings of both species towards the fall period. Salix planifolia produced more roots per cutting than P. balsamifera early in the season (i.e., May and June), but later in the season the differences between the two species were not great; root length showed no such trend. Differences among clones-populations in the rooting potential of cuttings were large for both species. Coefficients of variation for root number were lower in spring than later, during the growing season, for both P. balsamifera and S. planifolia. Seasonal trends in coefficients bf variation for root length were not as evident as for root number. These results have significant implications for site restoration in the Subarctic. To optimize the rooting ability of cuttings and minimize the differences among clones-populations in rooting potential, cuttings should be sampled early in the season before bud break or shortly thereafter.