The Boreal Forest Ecosystem
Located south of the world’s tundras and north of many mixed forest zones, the northern regions of Canada, the United States and Russia account for 93% of the Taiga biome [7]. Due to the harsh conditions, there is a low diversity of tree species. The Taiga biome is dominated by gymnosperms which do not produce energy intensive fruits but instead have exposed seeds [1,2]. Common gymnosperm tree species include pines, spruce, and other needle and cone bearing relatives. These forests are incredibly important to local rural and indigenous communities, but also to the global market as they account for 33% of lumber and 25% of paper exports [4].
Underneath the tree canopy is a surprising diversity of animal species that either migrate into and out of the region annually or that spend their entire time in the biome. These species include recognisable ones such as the brown bear, beaver, and the caribou reindeer [4,5]. Many species of bird migrate to the boreal forest in the breeding season to take advantage of the large insect populations in the warmer months, like the siberian moth and the mountain pine beetle [7]. Though lacking the biodiversity of the tropical forests, the boreal forests nevertheless support robust ecosystems capable of significant biological productivity annually.
The harsh conditions in the boreal forests are primarily caused by extremely low temperatures. A third of the ground underneath the tree canopy is kept below freezing even during the summer months, meaning there is permafrost in a large proportion of the biome [1]. Where there isn’t permafrost, the cold temperatures still limit evaporation, waterlogging the soils and creating extensive peatlands[7]. In fact, “Taiga” translates to “swamp forest” in Russian [7], an accurate description for these cold yet very wet ecosystems.
An Endangered Carbon Sink
When scientists and policy makers look for ways to mitigate climate change, they look for “carbon sinks” as a way to balance our planet’s “carbon sources” [9]. Put simply, global temperatures have been increasing from burning of fossil fuels, which releases “carbon” in the form of carbon dioxide, methane, and other greenhouse gasses into the atmosphere. A “carbon sink” would therefore be a process, often natural, that removes these greenhouse gasses from the atmosphere, or at least removes more “carbon” from the atmosphere than it releases.
Trees and plants are a very important part of the global ecosystem because they take in carbon dioxide and turn it into organic material composed largely of carbon (via photosynthesis), removing “carbon” from the atmosphere. When organic material dies and decomposes, the carbon is converted back into carbon dioxide and methane by bacteria and fungi and then released as waste back into the atmosphere. Ecosystems can either be “carbon sinks”, accumulating organic material faster than it can decompose or burn, or “carbon sources”, which is exactly the opposite.
The boreal forests are excellent “carbon sinks”, not because of the extensive forests but because of the frozen and waterlogged soils that cover the biome. Cold climatic conditions significantly slow down the activity of microbial decomposition which breaks down organic material [5], as does the waterlogging of soil and accumulation of peat [7]. The boreal forests are so good at storing organic carbon in its soils that 95% of its terrestrial carbon can be found in the soil, and only 5% in its living organisms above ground [6]. As long as the soil remains frozen over and waterlogged, the boreal forests will continue to remove more “carbon” from the atmosphere than it releases.
Unfortunately, the climate crisis is weakening the boreal forests’ ability to store carbon. Rising temperatures are increasing the prevalence of wildfires, melting permafrost, and drying up the peatlands, all of which cause the release of this stored “carbon” back into the atmosphere [8]. We will look at these threats to the boreal forests in the next installment of our Boreal Forest and the Climate Crisis series, and finally we will discuss what can be done to preserve this essential biome, and what steps have already been taken by various governments and organisations.
