Date of Award

12-1994

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Geography

Supervisor

Dr. G.M. MacDonald

Abstract

Forest fires occur frequently in the boreal forest of North America and greatly affect vegetation dynamics, biogeochemical cycles and resident human populations. Estimates of the frequency of boreal forest fires would be useful for understanding boreal ecosystems and managing the affects of fires on human populations. The objectives of this work were to investigate relations between fire frequency and climate change, vegetation type and waterbreaks in Wood Buffalo National Park (WBNP), located in northern Alberta. To address these objectives, four hypotheses were tested: 1) tree ring-width records from the boreal forest cap provide a proxy climate record; 2) annual area burned in the boreal forest varies in response to climate changes: 3) boreal forest fire frequency varies with differences in forest type and the proximity to waterbreaks: and 4) fossil pollen and macroscopic charcoal records from massive lake sediments can provide meaningful estimates or local fire frequency.

The first hypothesis was tested by constructing tree ring chronologies from 3 white spruce and two jack pine sites in WBNP. All five chronologies were significantly positively correlated with June precipitation in the growth year or the previous year, and were significantly negatively correlated with historical records of fire weather and annual area burned.

The second hypothesis was tested by analyzing historical records of annual area burned and climate, and free ring records of fire history and climate. Annual area burned was significantly negatively correlated with seasonal means of fire weather indices. The time since last fire was estimated using tree ring records from 166 sites located throughout WBNP. These records exhibited decadal and centennial scale variations in fire frequency. Comparisons with tree ring other proxy climate records suggest that these variations are related to climatic changes.

The third hypothesis was tested using survival analysis of the time since last fire records, disaggregated by dominant vegetation and the mean distance to waterbreaks. Sites dominated by jack pine (Pinus banksiana) and aspen (Populus tremuloides) exhibited significantly higher fire frequencies than did sites dominated by black spruce (Picea mariana) or white spruce (Picea glauca). Fire frequency increased with increased mean distance to waterbreaks.

The fourth hypothesis was tested by analyzing fossil pollen and charcoal records from two lakes at ~ 5 year resolution for 600 years. I compared their fire history records with local tree ring records of fire, and their mean fire intervals with regional fire frequency estimates for sites with similar vegetation and mean distances to waterbreaks. One lake exhibited a meaningful fire frequency estimate and the other lake did not. The poor fire frequency estimate was related to high sediment mixing and the lack of homogenous vegetation around the lake.

The results indicate that: 1) area burned and fire frequency in the bureal forest of northern Alberta varies temporally at the annual, decadal and centennial scales; 2) fire frequency varies spatially in relation to vegetation type and mean waterbreak distance: and 3) lakes with massive sediments can provide meaningful estimates of local fire frequency.

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