AGE STRUCTURE AND GROWTH OF UNDERSTORY WHITE SPRUCE UNDER ASPEN

Juvenile white spruce (Picea glauca (Moench) Voss) under an aspen (Pop ulus tremuloides Michx.) overstory were studied in nine boreal mixedwo od stands in west-central Alberta. In each stand, 50 understory white spruce were cut for stem analysis al ground level, 30, 70, 130 cm, and every 100 cm to tree height. Tn four stands, recruitment of these und erstory spruce occurred immediately after the disturbance, while in ot hers the recruitment was delayed several decades. The period of recrui tment was as short, as 15-20 years or continued for decades, producing an uneven-aged understory. Trees initiated on rotten logs had a sligh tly lower initial annual diameter increment but did not differ in heig ht growth compared with those initiated on normal forest floor. The an nual height increment increased as the trees grew in height, presumabl y as they overtopped successive layers of shading vegetation. When see dlings were less than 30 cm tall they grew less than 10 cm per year, b ut attained growth rates of 30 cm per year or more when they were tall er than 230 cm. Height growth rates for these understory trees were co mparable to reported growth rates of white spruce of similar size and age from clearcut areas.