Canada’s Arctic Tundra and the Impending “Carbon Bomb”

Written by: Bianca Marcellino



The Tundra biome is characterized by extreme cold weather, low biotic diversity and precipitation levels, short growing seasons, low-growing vegetation of simple structure, and nutrients available mostly in the form of dead organic matter. Only a small portion of the permafrost thaws each growing season, called the active layer, which limits the vegetation to low shrubs, sedges, flowering plants, and mosses, all with shallow roots and short reproductive cycles. 


In recent decades, the Tundra has rapidly warmed causing a variety of environmental effects including: melting sea ice resulting in increased water levels, shifting vegetation ranges, and release of CO2 stored in the permafrost. Presently, northern Tundra soils hold ~30% of the total soil organic carbon, which with the continued increase in temperature expected to occur over the next decades, threatening the release of this carbon sink; has alarmed the scientific community and gained the name the “Carbon Bomb”.


The warming temperatures may promote the expansion of the Canadian population into previously sparse areas such as the Tundra, fostered by the increased ability of the Tundra to support a greater abundance of vegetation (Deslippe 2011). This activity serves to counteract the lurking prospect of the carbon bomb ‘explosion’; however, the warming temperatures are also expected to drive native Arctic species further North if they are unable to adapt to the warming climate of their original regions. It is unclear whether the release of atmospheric carbon through the thawing of the permafrost will result in the Tundra becoming a carbon source via heightened microbial activity, or remain a carbon sink through increased vegetation growth.


The question arises - is it possible to plant native Arctic plants, which are well adapted to the current Tundra climate, as a mitigation strategy to help combat the “Carbon Bomb”? This could act to support Artic herbivores and their subsequent food webs, and potentially help to limit their displacement to more Northern areas, but may be impractical given the scale of the Canadian arctic and the limitations in our knowledge of how arctic ecosystems are being impacted by climate change.


This uncertainty clearly identifies the need for further study of Canada’s arctic in order to find the best tools to combat the carbon bomb.



Additonal Reading


National Geographic - Tundra Threats Explained

The Narwhal - Arctic tundra is 80 per cent permafrost. What happens when it thaws?

Sciencing - Plant Adaptations in the Tundra 




Deslippe, J. R., M. Hartmann, W. W. Mohn and S. W. Simard. 2011.  Long-term experimental manipulation of climate alters the ectomycorrhizal community of Betula nana in Arctic tundra. Global Change Biology. 17:1625-1636.


Gilg, O., K. M. Kovacs, J. Aars, J. Fort, G. Gauthier, D. Grémillet, R. A. Ims, H. Meltofte, J. Moreau, E. Post, N. M. Schmidt, G. Yannic and L. Bollache. 2012. Climate change and the ecology and evolution of Arctic vertebrates. The Year in Ecology and Conservation Biology 1249:166-190.


Steiglitz, M., A. Giblin, J. Hobbie, M. Williams and G. Kling. 2000. Stimulating the effects of climate change variability on carbon dynamics in Arctic tundra. Global Biochemical Cycles 14:1123-1136.


Treat, C. C. and S. Frolking. 2013. A permafrost carbon bomb? Nature Climate Change 3:865-867.


UC Berkeley Biomes Group, S. Pullen and K. Ballard. 2004. The Tundra Biome. Berkeley University of California.  Berkeley, CA, USA.


Late Fall Flowering Plant Profile - Witch Hazel

Written by: Mary Anne Young



What’s not to like about a plant that flowers while other plants are shutting down for the season?


American Witch Hazel (Hamamelis virginiana), is an understory shrub of North America’s eastern deciduous forests. Although it does have interesting wavy leaves which add character in the forest, or woodland landscape design, throughout the summer, its real beauty is in the late fall when its yellow fall colour drops and it begins to bloom. Few native plants in North America flower in this season, so it is always a delight to me to find a Witch Hazel in full bloom when other plants are winding down for the winter.




The flowers are unique, consisting of twisted thread-like petals with a pleasant scent. It also has an interesting seed dispersal mechanism where the woody seed capsules slowly mature over the course of a year and when it dries to a certain extent splits open to shoot 1-2 black seeds explosively up to 6m (20 feet) in every direction.




Here are some additional details about this fascinating species:


Form: Woody plant, medium to large shrub
Size: 3 – 4m tall and wide
Sun/Shade: Partial shade to full shade
Soil: Clay, Sand, Loam
Habitat: Deciduous forests, stream banks, clearings
Canadian Distribution: Ontario, Quebec, New Brunswick, Nova Scotia, Prince Edward Island (see map above, from VASCAN)




American Witch Hazel

(Hamamelis virginiana


View Plant



Witch Hazel is probably most popularly known for its use in medicine historically and today, where its leaves, bark, and twigs are used to make extracts and tinctures. Its tendency to grow along stream banks may have led to the myth that underground water could be found using a forked Witch Hazel branch (water witching).


Understory shrubs of the eastern deciduous forest have a tendency to be overlooked in favour of the delicate spring flowering wildflowers underfoot, or the towering trees overhead. However I challenge you to keep an eye out for Witch Hazel this fall as it puts on a show unrivalled by other forest plants at this time of the year.

A Plant's Worst Enemy

Written by: Carl-Adam Wegenschimmel


Honey Mushroom


One of the greatest adversaries to garden and wild plants is the great host of pathogens that regularly attack them. These organisms can belong to a variety of groups, including; fungi, bacteria, nematodes, and viruses. As human beings, we often consider the economic costs these organisms have on our economy, particularly in the agricultural, garden, and forest industries. However, pathogens also play natural roles in our ecosystems, killing sick plants and controlling the population growth of certain species that could otherwise dominate a community.


With the growing concern and insight into climate change, understanding how these understudied groups may affect plants and ecosystems is becoming increasingly important. One of the most noticeable of these groups is fungi!


Fungi attack their plant hosts in a variety of ways, some may first kill their hosts and feed on dead material (necrotrophs), which enter their hosts through wounds and natural openings. Other fungi feed on living tissue (biotrophs) which often enter their hosts in more specialized ways (Doehlemon et al. 2017).


Ulmus americana

Necrotrophs can sometimes be very destructive, especially when they are invasive species. A well-known example is Dutch Elm Disease (Ophiostoma novo-ulmi), which has severely reduced Elm tree abundance in North America. In this case, the fungus attacks trees with the aid of insects like the Native Elm Bark Beetle (Hylurgopinus rufipes) and the introduced European Elm Bark Beetle (Scolytus multistriatus). Dutch Elm Disease is believed to have originally been introduced from Asia, and so our native Elm trees have evolved little resistance to the fungus (Hubbes 1999). American Elm (Ulmus americana) and Rock Elm (Ulmus thomasii) have suffered the worst with Red Elm (Ulmus rubra) being slightly more resistant. The disease is spread to Elm trees when the beetles feed on twigs in spring time entering and slowly spreading into the trunk of the trees, blocking vascular tissues and eventually killing the host. The beetles are attracted to the diseased elms for breeding and subsequently bore holes into the infected Elms. Eggs are laid inside infected Elms where newly hatching beetles pick up spores and continue the cycle. 



Chrysomyxa pyrolae

Biotrophic fungi require living hosts in order to feed and have evolved specifically to interact with a living organism rather than a dead one. One of the most visible groups of these plant parasites are the rust fungi, which is one of the largest orders of fungi containing more than 8000 species worldwide (Lorrain et al. 2018). Some rusts cause little damage to their hosts whereas other species are better referred to as hemibiotrophs, which start off as seemingly benign biotrophs but eventually kill their host and act as necrotophic fungi (Koeck et al. 2011).





Some hemibiotrophic rusts are known to cause devastating damage to crops. Other species of rusts are rarely seen but have complex lifestyles like Chrysomyxa pyrolae seen here (right) on American Pyrola (Pyrola americana), which cycles between its Pyrola and Spruce (Picea spp.) hosts. Although this species does not necessarily kill its hosts, it has been observed to negatively affect seed crop in spruce trees (Sutherland et al, 2011).


There is still much to learn about the complex interactions between fungal pathogens and their plant hosts. Although with the continuous increase in scientific knowledge and technology, our understanding of these interactions is becoming clearer. Citizen science apps (like EDDMapS Ontario and iNaturalist) have also helped document the occurrence of these species, and may serve to help record the distribution of invasive species and maybe even prevent the spread of early invasions.





Doehlemann G, Ökmen B, Zhu W and Sharon A. 2017. Plant Pathogenic Fungi. Microbiol Spectr. 2017



Hubbes M. 1999. The American elm and Dutch elm disease. Forest. Chron. 75:265–273.


Koeck M, Hardham A. R.  and Dodds. 2011. The role of effectors of biotrophic and hemibiotrophic fungi in infection. Cell Microbiol. 2011 Dec; 13(12): 1849–1857. Published online 2011 Sep 14. 


Lorrain C, Gonçalves dos Santos K.C, Germain H, Hecker A and Duplessis S. 2018. Advances in understanding obligate biotrophy in rust fungi. New Phytologist (2019) 222: 1190–1206.


Sutherland R, Hopkinson S and Farris S.H. 2011. Inland spruce cone rust, Chrysomyxa pirolata, in Pyrola asarifolia and cones of Picea glauca, and morphology of the spore stages. Canadian Journal of Botany 62(11):2441-2447 · January 2011


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