Productivity And Phenology of Forests in the Algonquin-to-Adirondacks Corridor: Climatic Drivers and Recent Trends

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Stefanuk, Michael
forest , North America , Algonquin-to-Adirondacks , dendrochronology , remote sensing , sugar maple (Acer saccharum) , Random Forest , trend , response functions , phenology , productivity , climate
The phenology and productivity of temperate forests has changed across eastern North America in recent decades. However, these changes have varied spatially and temporally. And, while climate change has been an important cause of these changes in forest growth, the precise influence of climate remains unclear. This thesis presents the results of research which 1) tested for forest growth trends that could indicate that forest growth has changed in response to environmental stressors; and 2) assessed climate-growth relationships for different forest growth processes (phenology and productivity). Analysis was conducted at a regional scale within the Algonquin-to-Adirondacks (A2A) corridor, and at a sub-regional scale within the four geoclimatologically distinct ecoregions of A2A (Algonquin Highlands, Frontenac Arch, St. Lawrence Lowlands & Adirondack Mountains). We conducted two studies using different, but complimentary, methodologies. In the first study we used dendrochronology to study the growth of sugar maple (Acer saccharum) over a century (1912-2011). We found that sugar maple ring-widths declined recently in the Algonquin Highlands (- 46 mm2/year, 1993-2011) and Adirondack Mountains (- 33 mm2/year, 1991-2011), but that climate-growth relationships with temperature, precipitation and the SPEI drought index were limited (response function coefficients of ± 0.3). In the second study we used remote-sensing to study forest landscapes (i.e., pixels) over 26 years (1989-2014). We found that statistically significant (p < 0.05) trends in forest phenology and productivity occurred across only a small proportion of A2A (1-9 %), but that there was notable evidence of an extended growing season (+ 0.6-0.8 days/year) in the St. Lawrence Lowlands and Frontenac Arch ecoregions (25 % & 43 % respectively), driven by a delayed end to the growing season. Relationships between climate and forest growth were strong (pR2 > 80 %), and accumulated heating (> 4 0C) and chilling (< 20 0C) temperatures were the most important climatic variables for driving forest growth. Understanding climate-growth relationships for temperate forests in A2A will improve understandings of how forests have already responded to climate change, and will contribute to our capacity to predict how they may respond to future climate change.
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