Boreal forests in Canada are among the most susceptible terrestrial biomes to climate change (Price et al., 2013). This is largely due to the amplifying feedback effects of decreased surfaced albedo resulting from decreasing sea ice and shorter periods of winter snow cover (Price et al., 2013). For 1-6 °C increase in other parts of the continent, the boreal forests will experience an 8 °C warming (Stinziano and Way 2014). Unfortunately, the mean annual temperature in Canada’s boreal forest is anticipated to rise continuously by 4-5 °C by the end of this century (Boulanger et al., 2017).
On an individual scale, temperature variations impact the growth, mortality, productivity, recruitment, and succession of trees (Boulanger et al., 2017). In order to acclimate, species need to germinate, mature, reproduce and establish new recruits northward where temperature and precipitation conditions are more favourable (Goldblum and Rigg, 2005). On a regional scale, climate change can alter forest composition and the geographic distribution of tree species and biome as a whole (Boulanger et al., 2017), fire regimes will also shift accordingly (Lloyd et al., 2013). As a result of the individual and regional responses of boreal forests, a warmer climate will, therefore, result in the poleward shift of optimal climate zones for boreal forests by hundreds of kilometres (Goldblum and Rigg, 2005; Lloyd et al., 2013). This impact is most prominent in the southern boreal forest transition zones (Boulanger et al., 2017). With such advancement northward, Northeastern North America will eventually become the “climate refugium” for boreal forests (D’Orangevill et al., 2016).
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It is vital to investigate the impacts of climate change on boreal forests as the boreal forest biome is responsible for 20% of the total carbon sequestrated annually by forest ecosystems and contains a large fraction of the planet’s remaining unmanaged forests (D’Orangevill et al., 2016). Its change can greatly impact the global carbon cycle.
One of the most dominant and widely distributed tree species in North American boreal forest is White Spruce (Picea Glauca) (Gartner et al., 2011). Its unique characteristics—long life expectancy, low rates of mortality, periodic dispersal of large crops of seed, and shade tolerance— allow it to persist in the boreal forest for centuries (Gartner et al., 2011). However, the changing climate is imposing a tremendous challenge on White Spruce. The genus Picea generally decreases in abundance in times of warming climate (GoldBlum and Rigg, 2005) as their growth is optimal in a cool and wet climate (Lloyd et al., 2013). Lloyd et al discovered from their study in Alaska that changing climate will reduce the productivity of white spruce in the short-run and lead to contraction of their habitats to cooler moister parts of its range in Alaska in the long run (2013). The most important threshold in white spruce growth is growing season temperature (Lloyd et al., 2013). Climate change renders the possibility for crossing this threshold more frequent, adding more temperature and drought-induced stress onto white spruce to migrate. In fact, suitable habitat for white spruce had already shifted northwards by 207 km since 1960 (Gray and Hamann 2012 in Lloyd et al., 2013). Unfortunately, climate change is likely to outpace the rate which white spruce can adapt—either by colonizing new areas or recruitment or reducing reproduction (Lloyd et al., 2013)
Heat stressors also make white spruce more vulnerable to pest infestation and forest fire. Being one of the least fire-tolerant boreal tree species (Lafontain and Pavette, 2011), white spruce will likely suffer immensely from fire disturbances.
Study Area
The stripe of boreal forest along the border of Ontario and Quebec is the narrowest boreal biome in North America (Murray et al., 2017). The total width of the boreal forest is less than 500km. This bottleneck region is vulnerable to a warmer climate, due to the coupling effects of climate change, North Atlantic Oscillation and Pacific Decadal Oscillation climate phenomena (Boulanger et al., 2017; Murray et al., 2017). The study area span from the southern edge of James Bay, down to Lake Superior and Lake Huron. It is mainly composed of white birch (Betula papyrifera), white spruce (Picea glauca), black spruce (Picea mariana), Jack pine (Pinus banksiana), northern white cedar (Thuja occidentalis), and eastern hemlock (Tsuga canadensis) (Boulanger et al., 2017; Lafontain and Pavette, 2011; Murray et al., 2017).