Several kinds of seedbed mulch were used in an experiment to study frost heaving of white spruce (Picea glauca (Moench) Voss) in a nursery. Treatments consisted of silica gravel (of three sizes), hardwood sawdust, vermiculite, shredded sphagnum, mixed silica and sphagnum, and rye straw (the regular nursery mulch). These were applied to beds sown in the fall of 1958, 1959 and I960. Shading of beds during the winter between the first and second growing seasons was also examined.During the first growing season, several counts were made of the number of trees and weeds. At the beginning of the second growing season a count was made of the trees heaved and the residual stand. At the beginning of the third growing season, samples were taken for laboratory measurements of top length, root length, stem diameter, oven-dry weight and top-root ratio.The sawdust mulch was superior in most respects. It permitted the highest germination and survival, better prevention of heaving than rye straw, and better weed control than rye straw. Although the sawdust mulch treatment produced small and poorly balanced trees this was believed due chiefly to high bed density, and compared favourably with the rye straw. The use of hardwood sawdust as a mulch offered considerable advantage over the presently used rye-straw.Heaving was found to be a minor cause of mortality over the three year period examined. Shading of the beds offered no advantage in reducing this loss.
Methods for Successful Afforestation of a Weed Infested Clay Soil
