Boreal Forests And The Climate Crisis (Part 2)

by Isabel Siggers

The boreal forests represent 30% of the global forest area and are a major terrestrial carbon sink for our planet [1]. Unfortunately, this ecosystem is in danger, and could flip from being a carbon sink to a carbon source in the next few decades without intervention. This article will outline the threats facing the boreal forests. For more information about this ecosystem, please read our previous instalment “Boreal Forests and the Climate Crisis”.

How is the Boreal Forest a carbon sink?

As a refresher, an ecosystem is a carbon sink when it absorbs more “carbon” (in many different forms but usually CO₂ from the atmosphere) than it releases. Boreal Forests are an excellent carbon sink as the very cold temperatures prevent organic matter from decomposing which would return the carbon stored in the organic matter to the atmosphere. The waterlogged soils and accumulation of peat has a similar effect, which has led to most of the stored carbon (95%) being located in the Boreal Forests soil [2]. This carbon will remain trapped unless something makes the soil dryer or warmer.

Unfortunately, there are many factors already at work doing just that, and they are all linked to our changing climate.

Global Temperature Increase

 Many ecosystems are now threatened as a result of rising global temperatures due to climate change, but there is evidence that boreal forests will experience the largest degree of warming of all the forest biomes. Temperature increases could hit an average of 11 degrees Celsius by the end of the century which would seriously threaten the extensive permafrost covering the biome’s soils [4]. Such increases would warm the soils, accelerating the rate of organic matter decomposition and resulting in the release of more CO₂. Whilst increasing temperatures would encourage photosynthesis in above ground plants trapping more CO₂ from the atmosphere, unfortunately the evidence suggests that climate change will result in faster decomposition rates than photosynthesis. [3]. On balance, this means increasing global temperatures will lead to a net increase in carbon released from the boreal forests.

Increasing global temperatures also impacts boreal forest biodiversity, specifically the species makeup of its trees. Current tree species (largely gymnosperms) are well adapted to near or sub-zero Celsius temperatures but would do poorly in warmer temperatures [4]. Such changes in tree species abundance would threaten migrant bird populations as they would occur too fast to allow adequate time for adaptation [3]. 

Wildfires

Wildfires are important to maintain a healthy ecosystem, as they release pulses of nutrients from burnt trees back into the soil and allow shade intolerant species an opportunity to grow [3]. At the same time however, burning trees and other organic material releases CO₂ back into the atmosphere so wildfires are best for the ecosystem and planet in moderation. The changing climate with warmer conditions is likely to increase the risk, frequency and intensity of wildfires in the boreal forests, which could result in the biome’s extensive store of carbon being released back into the atmosphere on a massive scale over the coming decades. These wildfires are not restricted to the trees and plants above ground, but also threaten the soils saturated with yet to be decomposed organic matter [4].

Invasive species

Climate change also favours the northward migration of many species as the increased temperatures make environments more tolerable.  Unfortunately, this means the northward migration of invasive species/pests such as the Siberian moth and the Mountain pine beetle into the boreal forests [4]. These species threaten already vulnerable tree populations.

All the above threats to the boreal forests have interlocking feedbacks whereby the increasing influence of one worsens the other. For example, climate change allows for invasive species of insects to migrate north into the boreal forests. The more trees killed by invasive species, the more timber available to spark and fuel wildfires [5]. Wildfires in turn melt permafrost and dry the soils, accelerating the rate of organic matter decomposition. This makes the boreal forests less of a carbon sink and more of a carbon source, increasing the amount of carbon in the atmosphere and accelerating climate change. 

If curtailing the worst effects of climate change and limiting global average temperature increases is our goal, then protecting the boreal forests must be a priority going forward. Our final instalment in this series will discuss the policies already in place to protect the boreal forests and what more can be done to protect this important carbon sink for our planet.

Sources:

[1] Boreal Forests, UNECE, https://unece.org/forests/boreal-forests, accessed on 12 October 2022.[2] Bradshaw & Warkentin, 2015, Global estimates of boreal forest carbon stocks and flux, Global and Planetary Change volume 128, https://doi.org/10.1016/j.gloplacha.2015.02.004.[3] D.L.DeAngelis, 2019, Boreal Forest, Encyclopedia of Ecology volume 2, https://doi.org/10.1016/B978-008045405-4.00319-0. [4] Olivia Box, Climate Change’s Dangerous Effects on the Boreal Forest, JSTOR Daily, https://daily.jstor.org/climate-changes-dangerous-effects-on-the-boreal-forest/, accessed on 12 October 2022[5] European Green Deal: EU agrees to increase carbon removals through land use, forestry and agriculture, European Commission, https://ec.europa.eu/commission/presscorner/detail/%20en/ip_22_6784, accessed on 27 January 2023