DEVELOPMENT OF WHITE SPRUCE AND ALPINE FIR SEEDLINGS ON CUT-OVER AREAS IN THE CENTRAL INTERIOR OF BRITISH COLUMBIA

Abstract

Germination of white spruce and alpine fir was similar on mineral soil at all forest sites studied and averaged 33 per cent for spruce and 6 per cent for alpine fir.Mortality of seedlings in mineral soil was confined to the period of summer droughts. During this period maximum air temperatures approached 100° F., mineral soil exceeded 120° F. and humus 135° F. Water content of the upper 20 to 40 mm. of mineral soil was reduced below the wilting point and approximately 45 per cent of the seedlings died. The average root length of seedlings which died was 18 mm.; of those which survived, 37 mm. Greatest mortality occurred on fully exposed plots of dry habitats.On undisturbed seedbeds, germination of both species was very low. Seeds remained suspended and had insufficient contact with humic particles. Radicles of seeds which did germinate failed to reach compacted moist horizons. At the depth of root penetration, raw humus was at wilting point a few days after rain. A negligible number of seedlings of either species survived on raw humus to the end of the growing season.Shoot growth of both species ended at the beginning of August, while roots kept increasing in length until late in fall. The depth of root penetration on mineral seedbeds was greatest on sandy soils. At the end of the growing season alpine fir seedlings were larger than spruce seedlings.The main cause of seedling mortality on both types of seedbed appears to be the water deficit in the root zone. Increased mortality on fully exposed plots can be attributed to the direct heating of the living tissue under water stress.