Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Biology

Program Name/Specialization

Integrative Biology

Faculty/School

Faculty of Science

First Advisor

Jennifer Baltzer

Advisor Role

Advisor

Abstract

Black spruce (Picea mariana) and jack pine (Pinus banksiana) both release a large majority of their seeds after fire and thus experience large pulses of recruitment during these punctuated events. Global warming is driving intensification of the wildfire regime in the boreal forest, which is resulting in shifts from coniferous to deciduous dominated forests in some parts of the boreal forest of North America. This shift can present consequences for forest structure, ecosystem dynamics, carbon cycling, and wildlife habitat.

During 2014, the Northwest Territories experienced a historically unprecedented fire year with 3.4 million hectares of forest burning. For two summers post-fire, I measured 1) black spruce seed rain at 25 black spruce dominated locations, and 2) seedling establishment at 224 conifer-dominated locations across the Northwest Territories. Using generalized linear mixed models with candidate model-based hypotheses, I sought to estimate 1) whether fire characteristics or ecological legacies better predict total and viable black spruce seed rain; 2a) the drivers of species-specific seedling establishment post-fire, and 2b) whether there is evidence of a change in species dominance following this extreme fire season.

Models with variables linked to fire characteristics provided the best fit to observed variations in both total and viable seed rain. Canopy consumption by fire was a significant predictor of viable seed rain; stands that experienced a less severe burn had more viable seeds. After two years of data collection on the Taiga Plains, both pre-fire black spruce-dominated and pre-fire mixed stands showed a significant decrease in black spruce relative abundance and an increase in the proportion of jack pine. On the Taiga Shield (where there was only one year of data collected), deciduous seedlings were more abundant.

This research has demonstrated key findings about post-fire successional dynamics and patterns of dominance in the Northwest Territories. Increased canopy combustion is likely to result in decreased availability of viable black spruce seed rain, with implications for regeneration processes such as reduced recruitment rates. Differences in post-fire establishment patterns were seen across the Taiga Plains and Taiga Shield, suggesting that the two areas are responding differently to altered disturbances as a result of climate change. These results can be used in ongoing modeling efforts to determine how future changes to this landscape will modify forest composition, wildlife habitat, and forest processes.

Convocation Year

2017

Convocation Season

Fall

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