Willow, Birch, and Jack Pine… Oh My!: How the Boreal Forest Changes Over Time

Has the boreal forest always been a boreal forest? How do vegetation communities change with age? One thing for certain is that northern boreal forests are young. Compared to the redwood forests of California for example, Alberta’s boreal forest is a ‘baby’. That being said, it’s no baby in size. The boreal forest region in Alberta covers over 55% of the province and is a ‘hot spot’ for ecological diversity.

The forested parts of Alberta figured here are dominated by the boreal forest. The boreal region is renowned for its ecological diversity and is home to hundreds of plants and animals (created by Christina Poletto).

Why is Alberta’s boreal forest so young and how has it changed? Some 12,000 years ago, ice sheets that covered Alberta began to melt and the landscape opened. The Laurentide Ice Sheet retreated to the northeast so that the northwest corner of Alberta was the first region to become free of ice. The newly opened landscape was a productive steppe-tundra environment that lasted for a short period. Species like birch and alder were dominant while smaller shrubs of grasses and willow covered the remaining landscape.

Thanks to palaeoenvironmental reconstructions, we know that once the ice left Alberta, the landscape immediately after probably looked similar to this vista (tundra of the Arctic National Wildlife Refuge by U.S. Fish and Wildlife Services, public domain).

After steppe vegetation, a warmer and drier climate promoted a forest abundant with deciduous trees. Around 6000 years ago, pine trees appeared in the boreal forest region. Species like spruce, birch, and alder became more abundant, which suggests a return to cooler and wetter conditions. During this time, sphagnum, or peat moss, is prominent in the palaeoenvironmental record indicating intensive peatland formation. With the arrival of these species, the boreal forest was similar to that of today, indicating relatively stable environmental conditions for the past 5,000 years.

Different features on the landscape promote different plant species occupation. Near the water margins are smaller shrubs and black spruce. Further to the back, stands of jack pine dominate due to drier soils ( photograph Christina Poletto).

While the boreal forest was stable over the long term, it still changed over shorter intervals and varied from place to place due to soil conditions, moisture levels, and topographic variability. Well drained soils sustain more tree species like birch and jack pine while wetlands host species like shrubs, grasses, and willow. Overall though, the major contributor to change and diversity in the boreal forest is fire.

Forest fires are a common part of the boreal forest cycle, and while they are destructive, small fires are the reason why the region has so much ecological diversity (“Fire – Forest DSC_7139” by Cameron Strandberg licensed under CC BY-2.0).

Fire is thought to be a devastating, destructive force, especially when it directly affects humans and destroys homes, like the Fort McMurray fire in May of 2016. However, in the boreal forest, fire is needed for species to survive. Jack pine (Pinus banksiana) have evolved serotinous cones, which means they require an environmental trigger (in this case, intense heat) to open and disperse their seeds.

The boreal forest relies on successional communities to maintain its ecological diversity. Fires prevent forests from becoming overgrown and monopolized by specific plant species by removing dead organic material and providing food for new plants to grow. A more open canopy allows more light on the forest floor and this leads to quicker growth of plants like berry bushes, fireweed, grasses, and shrubs. Plant species return to regions shortly after fires when vegetation mosaics and the animal communities they support re-establish themselves. If you walked into a forest a few years after a fire, it could look much more open and grassier than it did twenty years earlier. This successional cycle and the relatively high frequency of fires in Alberta are part of what makes our forests ‘young’.

Following a fire, fireweed (Chamaenerion angustifolium) is one of the first species to reappear and help redevelop the landscape. The carbonized plant material after fires provides species with food to grow and flourish (“Fire Weed at West For burn above Fern Creek” by Tim Engleman, licensed under CC BY-SA 2.0).

This image shows the forest floor one, two, and three years after a fire (from L to R respectively). Often after a fire, the canopy has opened up and allows for more light to reach the forest floor giving shorter grasses and shrubs a chance to establish themselves (“Boreal pine forest after fire 2” by Hannuis, public domain).

What about humans? Have we affected vegetation in the boreal forest? Yes! Since 1867, forests had been managed to ensure that they were not completely stripped of trees during logging and that forest reserves would be kept ‘green’ and intact. There was also a strong emphasis on the prevention and suppression of forest fires. In more recent years, economic development and climate change has shifted treelines and changed soil conditions in some areas with resulting changes to species compositions. With modern initiatives, the impacts of humans have lessened, and the boreal forest continues to flourish. The boreal forest may be young, but it has seen so much change in its lifetime. The successional nature of the forest in relation to species, fire, and climate, means that vegetation communities will continue to change.

Today, recognizing the changing dynamics of boreal forests helps us appreciate that what we see now wasn’t always the case. Reconstructing what forests once looked like enables an understanding of how First Nations and early settlers lived within changing landscapes. This history and the ability to anticipate future changes allows us to better understand our role in Alberta’s forests.

Written by: Christina Poletto (Christina is an M.A. student in the Department of Anthropology at the University of Alberta)

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