The Taiga or Boreal Forest Biome

The TAIGA or BOREAL FOREST Biome

ABIOTIC FACTORS

The taiga or boreal forest is the world's second largest biome, stretching throughout North America, Europe and Asia and covering 11,5% of Earth's land. Canada, Alaska, the United States, Sweden, Finland, Norway, Scotland, Iceland, Russia, Kazakhstan, Mongolia and Japan all have taiga areas, although Canada and Russia have the largest areas by far. In the US and Canada, the terms taiga and boreal forest are not used interchangeably, and instead boreal forest refers to only the more southerly part of the biome.

Due to its high latitude, the taiga has the lowest average annual temperatures next to the tundra. Its climate can be described as subarctic, and is defined by long, cold winters, as well as short mild summers which are usually 1-3 months in length. Summer days can be long and some areas experience midnight sun in summer, as well as polar nights in winter. Permafrost or discontinuous permafrost occur in many regions.

Precipitation levels are generally low but slightly higher in summer. Snow may melt in this time which can contribute to swampy, moist grounds as it still too cool for much evaporation, although in comparison to winter the air is humid. Taigas have infertile, acidic, podzol soils, particularly as low temperatures slow decomposition processes and there is little nutrient gain by precipitation.

Case Study 1

The Nitrogen Cycle in Taiga Ecosystems

Taiga ecosystems are characterized by low nitrogen availability. In his doctoral thesis, biologist Róbert Blaško investigated the development of the nitrogen cycle in boreal forests. 

Many taiga trees have nitrogen fixing bacteria in their root nodules, such as the Frankia actinobacteria. These turn nitrogen from the air into nitrates the plant can use. 

Despite this, Blaško found that, in his study areas in Sweden, nitrogen availability declines with ecosystem age. For example, he noticed a 20% decline in percentage of nitrogen in conifer needles when comparing a 150 and 560 year old taiga forest.

He suggested this may be due to changes in the microbial community. For example, plants more prevalent in older ecosystems may have different nitrogen fixing bacteria that provide less nitrates, or abiotic factors may arise or increase that limit nitrogen fixation.

Case Study 3

Snowshoe Hare and Lynx as a Predator - Prey relationship 

The snowshoe hare is adapted to its snowy environment with large and furry hind paws that allow fast movement without sinking into snow, as well as it's thick fur that protects against the cold and changes colour to help it blend into its surroundings depending on the season. The lynx also has long, dense fur and “snowshoes”, as well as excellent sight and hearing, which is aided by the tufts of fur on its ears. 

Whilst the snowshoe hare is a herbivore that lives on grass, leaves and bark, the lynx is a predator, and its primary prey is the snowshoe hare. They can make up over 70% of its diet.

This famous dataset, credited to the Hudson's Bay Company, illustrates the relationship between populations of lynx and snowshoe hare in Canadian taiga. 

Their population sizes increase and decrease alternately and cyclically. If hares are abundant, the lynx population will soon grow too as they have more food. When the lynx population reaches a certain size the hare population will start to shrink as so many of them are eaten by the lynx. Soon after this, the lynx population will begin to shrink due to lack of food. Now the hare population will grow again due to low predation levels. Thus, the cycle repeats itself, lasting usually about ten years.

Climate Change and Human Impact

"Since the 1850s, the mean annual temperature in the boreal region of Canada 
has risen by 0,5°C to 3°C, with increases greater than 2°C West of the Manitoba-Ontario border. The Intergovernmental Panel on Climate Change recently published its fifth assessment report, and it concluded that increases of 2°C in mean annual temperature by 2050 are highly probable, and mean annual temperatures across the Canadian boreal forest zone could be 4-5°C warmer by 2100", says Mark Johnston, Canadian forest scientist. As the global warming trend continues, the boreal forest is not left untouched. Rising temperatures will have lasting effects on it.

Within Canada, for example, warmer temperatures and changes to the distribution of annual precipitation will cause highly damaging droughts in some areas. Furthermore, large wildfires are expected to rise in number. Of course the burning of the forest itself releases CO2, perpetuating the problem. Another threat is the outbreak of forest insects. A relatively small temperature change can cause a population to explode if it moves further towards the optimum range of the species. In British Columbia, the Mountain Pine Beetle has already caused considerable damage to trees, and will probably spread eastwards in the next decades. It is also highly important to note that about 40% of the Canadian boreal forest and many taiga ecosystems across the globe are underlain by a permafrost. In many areas, this is melting and degrading irreversibly. This means that, for several decades, a repeated process of forest decline and re-establishment will occur as flora is forced to adapt to the lack of permafrost and soft, wet grounds. This process also releases significant amounts of CO2 and methane, only amplifying the greenhouse gas problem at the root of global warming.

Other pressures are human developments destructive to habitats of native plants and animals. Urban expansion, building of roads and infrastructure, the timber industry, the killing of predators to protect humans' livestock and the exploitation of minerals are some examples of practices threatening biodiversity on smaller scales. A key controversy in Canada's boreal regions is the mining of tar or oil sands. Hectares of forest must be cut down and waste products pollute land and water.

In many areas of Canada, bitumen can be found in so called tar sands. These are mined and the bitumen is processed to produce oil.  Tar sands can be extracted in two ways; surface mining or well extraction. In surface mining, all trees and soil are removed to reveal oil sand deposits. The alternative method means drilling wells to reach bitumen soaked sand deposits. Both are highly damaging to surrounding ecosystems, usually taiga forest. Tar sands make up 40% of Canada’s oil production, and 20% of the USA’s annual oil consumed stems from Canadian sources. This goes to show how ingrained environmentally damaging industries are in our economy and lives. 
Another important industry of Canada's which has contributed to deforestation is the timber industry, but this is now jeopardised by rising temperatures. 

As temperatures rise many tree species migrate further and further north to find suitable growing conditions, although at a slower pace than climate change. Increased transformations of forests to grass or shrub lands may occur, especially under increased drought conditions. The aforementioned fire and insect outbreaks will further limit the amount of harvestable material. Climate change favours pioneer species, so hardier species which can be the first to colonize previously biodiverse, but then damaged or disrupted ecosystems. Examples are pinus and populus trees. Although climax species such as picea or abies trees may decline, this opens up opportunities for the timber industry to make use of trees such as the populus.

Altogether, it is important to remember that, as scientist Susanne Tautenhahn puts it, "boreal forests are some of the largest stores of carbon on the earth", as well as some of our most important photosynthesisers (as the largest biome on earth) and therefore any changes to them will leave a permanent impact on our global climate.