Comparison of white and black spruce growth within the Boreal Forest-Tundra ecotone in the Northwest Territories

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Featherstone, Emily
The current and predicted implications of climate change are one of the most pressing global issues we face today. There is a strong indication that forests, especially in northern ecozones such as the boreal forest, are likely to experience some of the greatest impacts from climate change. Using dendrochronology (tree-ring analysis), this study examined the growth of trees, specifically white spruce (Picea glauca) and black spruce (Picea mariana), found at a site within the forest-tundra ecotone of the central Northwest Territories. The goal of this study was to conduct research that will contribute towards a better understanding of how the boreal forest-tundra ecotone is responding to climate change. Results show that while black and white spruce had similar growth trends during the 19th century, they have shown changes in more recent years and do not grow as similarly as they used to. There has also been a shift in growth in both species in the last century, in which white spruce appears to be decreasing in growth and black spruce appears to be increasing in growth. Pearson correlation tests on data between 1901-2010 found no significant relationship between climate trends (summer temperature and precipitation) and white spruce growth, but found significant relationships between climate trends and black spruce growth. To further examine climate-growth relationships, the data was divided into two time periods. Significant correlation tests were detected between black spruce ring widths and summer temperatures during 1920-1960, and summer precipitation during 1960-2010. Based on these results, is important to consider that there may be other local environmental factors influencing growth of each species (such as species competition, forest disturbances, soil moisture/nutrients, wildfires, etc.). Future studies could include an analysis of pointer years (specifically 2007 and 1939 from this study) to obtain more information relating to extreme environmental changes that have occurred by identifying variables that cause abrupt responses in tree growth patterns.
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