In this thesis, the postglacial spread of three ecologically distinct species, Picea mariana (black spruce), Picea glauca (white spruce), and Pinus banksiana (jack pine), across the western interior of Canada are presented. The fossil pollen records from the sediments of thirteen lakes are used in reconstructing the population expansions of the three tree taxa. The objectives of this study are to examine temporal and spatial patterns in the growth of the populations and to determine if intraspecific and interspecific variations exist across a range of latitudes and elevations. Pollen accumulation rates (PAR) are calculated from pollen grain counts and sedimentation rates throughout the early-to mid-Holocene, and are used to represent the population level at the time of pollen deposition. Exponential equations are used to calculate population growth rates. Three dimensional diagrams (time, space, abundance) are constructed to illustrate the spread of the populations. The rates of population growth varied from south to north for all three species. Jack pine, on average had slower population growth rates, and its expansion across the region began over 3,000 years later than, and lasted approximately 1,000 years longer than the two spruce species. All three tree taxa experienced reduced rates of population growth at high elevation sites in the north. These variations are examined in light of the changing and static physical and botanical environmental conditions occurring during expansion.

Master of Science (MSc)

Thesis