EFFECTS OF ESCAPED SETTLEMENT FIRES AND LOGGING ON FOREST COMPOSITIONIN THE MIXEDWOOD BOREAL FOREST

The southern edge of the boreal forest in central Saskatchewan, Canada , has had its forest composition changed in the first decades of this century, primarily by logging and escaped fires from adjacent agricult ural clearance. Three timber berths were established in 1884 within an d immediately adjacent to the present southern half of Prince Albert N ational Park (established in 1927). These timber berths were selective ly logged for saw timber between 1900 and 1918. Between 1907 and 1918, an average of 70 trees per hectare were removed by selective logging. Most of these trees were white spruce (Picea glauca (Moench) Voss). S ince logging companies were required to remove all merchantable trees with a basal diameter greater than 25 cm, it is estimated that between 28 and 54% of the canopy trees were removed. Between 1883 and 1942, 8 1% of the timber berths were burned two or more times by crown fires t hat spread through the study area from adjacent agricultural clearance s 30 km or more away. By 1945, agricultural clearance was largely comp lete and the clearance-caused fires stopped. The changes in tree compo sition were determined by transition probabilities between forest surv eys taken in 1883 and 1994. Forests subjected to short-interval, clear ance-caused fires but no logging were significantly reduced in their a bundance of sexually reproducing trees such as white spruce, but incre ased in trees with either vegetative reproduction (i.e., underground s tems, not just basal sprouts) or serotinous cones, such as aspen (Popu lus tremuloides Michx.) and jack pine (Pinus banksiana Lamb.), respect ively. Transition probabilities for forests experiencing both short-in terval, clearance-caused fires and logging reveal an even more marked compositional change in this direction.