Boreal Forests

in a Changing World

By Ben Golan

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Boreal Forests Today In a world facing climate change, nothing is certain but the change itself. Facing this uncertainty, we must ask ourselves, will we adapt to this change? Will we steer this new world in a direction that works for us? Or will we collapse? Will our own wrongdoings be our demise? We can only speculate as to what our future holds, but through research we can whittle this speculation down to educated guesses. Through recent and proxy data, we know that climate change is a result of an increased release of greenhouse gases into our atmosphere (Figure 2) (15). This shift in the composition of our atmosphere (and consequently the shift in Earth’s temperature) will directly impact the composition of Earth’s surface, specifically the structure of climates and biomes (15). The exact future of certain biomes and climates is not clear but climate scientists expect an expansion of our deserts and the acidification of our oceans (16). It is expected that some terrestrial biomes will migrate to more suitable temperatures, others will thrive and some will fade (16). My research concerns the biome, boreal forests. I aim to evaluate the characterizations of boreal forests, species that inhabit boreal forests, and the influences of and on boreal forests in hopes of answering the question, what does the future hold for the Taiga? The evaluation of this biome must first start with an understanding of what a biome is: a major ecological community of flora and fauna adapted to the particular environmental condition in which they occur (4). When discussing boreal forests (also known as the Taiga) we are discussing a community of flora and fauna adapted to a band that stretches across the Northern Hemisphere, roughly between 50 and 70 degrees North latitude (27).

How Greenhouse Gases Work: The sun releases energy in the form of shortwave radiation (13). This radiation travels through space until it reaches Earth, at which point it does one of three things: 29% of the incoming solar radiation is reflected off of Earth’s atmosphere, 23% is absorbed by Earth’s atmosphere and 48% is absorbed by Earth’s surface (13). This last 48% is then rereleased back out of Earth’s surface as longwave radiation (13). And this is where the greenhouse gases come into play. Greenhouse gases in the atmosphere absorb this longwave radiation and “vibrate” (13). This vibration releases heat and is responsible for warming Earth’s atmosphere (13). Without greenhouse gases, life on Earth would not exist. However, with too many greenhouse gases the same would be true. With the recent drastic increase in greenhouse gases, our atmosphere is warming at a rate never seen before (16).

Figure 2 (11) This drastically fast warming of Earth’s atmosphere brings with it changes to Earth’s climate systems: climates will migrate, change, adapt and disappear (16).  

Figure 1: Shown in green and extending from Alaska to Newfoundland in North America and from Northern Sandinavia to Siberia in Eurasia, boreal forests are the largest terrestrial biome on Earth (27).

Figure 1 (24)

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Given its size, it is not surprising that this biome has the greatest temperature range on the planet (16). These forests’ average annual temperatures vary between negative 5 degrees Celsius (23 degrees Fahrenheit) and 5 degrees Celsius (41 degrees Fahrenheit) (16). Its size also serves for varying precipitation rates as well: between 20 and 500 millimeters with most of this precipitation falling in the form of snow (27). However, size is not the Taiga’s only climate-controlling factor. Boreal forests are located in high Northern latitudes affecting its climate type and seasons (26). Boreal forests, sitting south of tundra and north of deciduous forests/grasslands are described as a subarctic climate characterized by long, cold winters and short, cool summers (16). This subarctic climate type is dominated by the Westerlies and cyclonic activity during the summer and the polar high and Easterlies during the winter (continental polar air masses) (7). This cyclonic activity is responsible for most of the precipitation that falls in the subarctic regions and its seasonality (during the few summer months) (7). The polar high-pressure zone during the winter is responsible for the little precipitation that falls during this time of the year (7).

The flora and fauna that live within this biome share commonalities adapted to this region (16). In other words, these species have adapted to an area that experiences long, harsh, dark winters and short, cool, moist summers (16). These unique and unforgiving circumstances serve for a biome with low biodiversity (16). Low sun angles, frigid temperatures, strong winds and little precipitation drive a unique evolutionary trail and consequently a particular set of species (26).

As seen in figure 3, the lack of interaction with the maritime air masses serves for low precipitation/humidity and large temperature ranges (16, 17). Defined by a subarctic climate, Yatsuk, Russia has a wide temperature range (roughly negative 40 to 15 degrees Celsius) and a low amount of precipitation (roughly 10 to 50 millimeters), both peaking in the summer months (17). A climograph like this would be typical of any location found in the Taiga (16).  

Typical flora found in boreal forests --An over story of trees, primarily coniferous, such as spruce, fir, larch, hemlock and pine coupled with some species of deciduous poplar, aspen and birch. --An under story primarily of herbs, mosses and lichens, but that also includes wildflowers and grasses. (16, 26, 19)

Typical fauna found in boreal forests --The main carnivores are bears, felids (ranging from the large Siberian Tiger to the small bobcat) and canids (gray wolves and foxes). --The mammalian herbivores include elk, deer, moose, muskrats, weasels, hares, chipmunks, shrews and bats. --The birds of prey include hawks, eagles, falcons and owls. --Other birds include woodpeckers, herons, storks, bitterns, swans, geese, ducks, larks, swallows, warblers, buntings, starlings, crows and thrushes. --Insect pests include forest tent caterpillars, birch leafminers, gypsy moths and mountain bark beetles. (16, 26, 19)

Figure 3 (17)

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The growing season in the Taiga is short and explosive (19). Snow melt, little evaporation and long day length in the summer means a moist ground and a lot of sunlight (19). These conditions serve for an intense 3-month period of uniform growth (19). Growth is uniform because trees that grow too slowly lose exposure to sunlight and trees that grow too quickly risk exposure to frigid wind (18).

As mentioned before, coniferous trees dominate boreal forests (16). Coniferous trees have needles rather than broad leaves, minimizing snow build-up, heat-loss and evapotranspiration (19). These needles are perfect for keeping the trees warm. These coniferous trees are also well adapted to the thin, nutrient-poor and acidic soils dictated by thick layers of permafrost (27). The non-coniferous, broadleaf trees (poplar, aspen and birch) lose their leaves before the heaviest snows of winter to minimize evapotranspiration and heavy snow build-up (27). In essence, retaining heat and minimizing contact with the wind and snow are the most crucial adaptations to survive in the boreal forest. And the fauna of the boreal region share adaptations with similar goals. To minimize contact with the snow and wind, many animals have specialized footing and thick, insulating fur (27). Some species also avoid the coldest months altogether by migrating or hibernating until the warmer months succeed again (27).

The boreal species have learned to thrive in a subarctic climate by adopting one major technique: avoidance. Mutation has led to pine needles that are able to avoid heavy snow build-up (19). Natural selection has driven the progression of thick coats, helping the black bear’s skin to avoid the frigid temperatures (27). Gene flow has encouraged uniform growth and helped the over-story of trees avoid the darkness (18). Genetic drift has shortened tree roots, helping tree species avoid the thick layers of permafrost (18). Through the combined efforts of evolutionary forces, boreal species have adapted to the Taiga (18). But what forces drive the biome as a whole?

Figure 5: The Snowshoe hare (Lepus americanus), one of the indigenous hares to the boreal forest, is well adapted to this subarctic climate (26). As its name implies, the Snowshoe hare has feet adapted for walking on snow and ice (26). Its feet and white fur (grown in the winter to better camouflage itself) help it to avoid predation from lynxes, foxes and others (27). Its agility, ability to blend in, and nocturnal behavior has helped this species thrive in an otherwise unforgiving climate (26).

Figure 4: The pine needles of this Norway Spruce (Picea abies) are covered in a wax-like substance, helping to shed any unwanted snow build-up (26). The Norway Spruce keeps its needles year-round as they help retain heat in several other ways as well (26). The cone pictured above acts as the seeds’ keeper. It protects the seeds from the freezing temperatures and cold winds of winter (26). When the summer months come and the growing season begins, the cones will drop and release the seeds (26).

Figure 5 (25): The Snowshoe Hare

Figure 4 (8): The Norway Spruce

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The Influences of Boreal Forests Through the process of photosynthesis, plants sequester carbon from the atmosphere (6). Plants “suck up” carbon dioxide through stomates in their leaves and intake water through their roots (6). These two compounds are then collected in the plant’s chloroplast (6). Energy from red and blue light is then harvested and used to create a chemical reaction within the chloroplast (6). The products of this chemical reaction are sugars (used by the plant) and oxygen (expelled by the plant) (6).

This process is responsible for the oxygen on Earth and an important part of the carbon cycle (6). Without it, animals could not exist. Knowing this, one can see the integral value of plants and the forested biomes to Earth’s systems. Boreal forests, with 182 tons per acre, are responsible for storing the most carbon of any terrestrial biome on Earth (5).

Once this carbon is stored in the plant, it is not rereleased until the plant goes through decomposition (20). Once the plant is dead, an energy source (heat, light or electricity) breaks down the compounds of said plant through the process of decomposition (20). Boreal forests offer very little heat, light or electricity sources making the decomposition rate very slow within these regions (20, 22). A slow decomposition rate means a high rate of carbon storage (20). Effective carbon storage works well against an anthropogenic change in atmosphere composition (15). And the vast amounts of snow work well against an Earth facing anthropogenic warming (16). The large amount of snow cover in the boreal regions offers high albedo (2). Albedo is a measure of the reflectivity of the Earth’s surface (2). A surface with high albedo reflects a high amount of incoming shortwave radiation and repels potential heat (2). A surface with low albedo absorbs a high amount of incoming shortwave radiation and embraces potential heat (2). Essentially, boreal forests act as an important buffer to climate change. The storage of carbon in the trees and permafrost offer a large contribution to the Northern Hemisphere terrestrial carbon sink (12). And the slow decomposition and permafrost melting rates ensure the carbon will stay stored for a long time (6, 5). The large white surface acts as a trampoline and “bounces” the incoming solar radiation back out to space effectively slowing down global warming (2). These processes are essential to helping humans mitigate climate change and boreal forests are the catalyst to this mitigation. However, these forests are, themselves, susceptible to the impacts of climate change.

Figure 6 (3): The chemical process of photosynthesis

Figure 7 (1): The reflective potential of lighter surfaces

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The Influences on Boreal Forests Although nothing in climate change is “certain but the change itself”, climate scientists can agree on several expectations. Within the Intergovernmental Panel on Climate Change’s Fifth Assessment Synthesis Report, climate scientists offer a summary of modern thought on climate change (15). Within the report are observed events caused by climate change and expected events caused by climate change (15).

Figure 8 (15): The Earths on the left represent modern changes in average surface temperature and average precipitation due to climate change. The Earths on the right represent the expected changes.

The impacts of climate change are expected to affect certain regions more heavily. The higher northern latitudes are expected to see a disproportionately high rise in average surface temperature and average precipitation (15).

OBSERVED EVENTS (15): • The acidification of the oceans • Sea levels have risen • The atmosphere and ocean have

warmed • The amount of snow and ice have

diminished • Precipitation has increased over

the mid-latitude land areas of the Northern Hemisphere

• Permafrost temperatures have increased

 

EXPECTED EVENTS (15): • Surface temperature is projected

to rise over the 21st century • Heat waves will occur more often

and last longer • Extreme precipitation events will

become more intense and frequent • The ocean will continue to warm

and acidify • The sea level will continue to rise

 

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The Future of Boreal Forests The expected events are essentially a continuation of what can already be observed and these expected events are very likely to happen (15). However, their severity will depend on future anthropogenic emissions and natural climate variability (15). The severity will also depend on the region being discussed (15). The higher Northern latitudes are expected to see the highest levels of impact leaving the boreal ecosystems at high risk (15). The increase of surface temperatures in the higher Northern latitudes will cause a projected decrease of 15% to 55% of glacier volume (21). There will be a significant loss of overall ice and snow cover and the upper 3.5 meters of permafrost is projected to decrease between 37% and 81% (21). This warming will cause a significant increase in precipitation and lead to a change in seasonality (15). Winters will be shorter, summers will be longer and the fire season will be more intense and start earlier (5, 22).

Today, the boreal region is confined to the region between 50 degrees North and 70 degrees North (27).

Boreal forests are expected to migrate north into what is now the southern tundra region (23).

Figure 9 (9)

Figure 10 (10)

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These changes will cause a shift in the biodiversity of boreal forests and an overall migration of terrestrial species (12). The forests will most likely “chase” the cooler temperatures and migrate to higher latitudes and elevations (12). The trees will expand into tundra and most likely die back along southern prairie ecotones (23). There may be a loss of evergreen trees and a shift towards more deciduous trees (23). White spruce tree growth will decline due to moisture-related stress (21). Pine tree populations will decline due to pest-related stress (particularly from the mountain bark beetle) (28). Siberian forests may collapse in some areas and become more evergreen in the north (23). The forest as a whole will shift to a younger age class in response to an increase in fires and pests (22, 28). The current mosaic structure of boreal forests will most likely change (21). And the growing season will be longer (12). The fauna will face lower extinction rates than the flora, as their ability to move will allow them to migrate quickly (5). In response to the shift in season lengths and an overall warmer surface temperature, migration and hibernation periods will be shorter and start later (12). There will be a significant increase in pest species and a possible decline in small mammal species (28, 21). Species that were once limited to lower latitudes will be able to expand into the now warmer higher latitudes (21). This shift in biodiversity will bring with it a shift in species/population interactions and potentially introduce invasive species (5). As a whole, the boreal forest cycles face great changes. The carbon storage ability drops significantly as surface temperatures warm. Higher temperatures mean a faster rate of decomposition and a shorter amount of time the carbon is stored (20). The permafrost will melt releasing the carbon stored within it, introducing it back into the atmosphere (21, 6). All the while, tree mortality rates will increase and reduce the total photosynthetic capacity of the forest (23, 6). In addition to the changes facing the carbon cycle, the radiation cycle will be affected by the loss of snow coverage (21). As surface snow and ice melt, the albedo potential drops leading to a larger amount of incoming solar radiation absorbed (5). With this absorption comes warmer surface temperatures and higher instances of the fire and succession cycle (2, 22):

1. Fire releases carbon stored in trees, leaf litter and soils (22). 2. Blackened soil has decreased albedo. The decreased albedo raises soil

temperatures, melts permafrost and accelerates decomposition rates (releasing more carbon dioxide) (22).

3. Deciduous trees are the first species to recolonize the site (22). The sequestration of carbon begins again (6).

4. Evergreen species bounce back and shade out the deciduous species (22). 5. The permafrost layer is eventually reestablished (22). 6. Carbon is accumulated in the trees, leaf litter and humus, setting the stage for the

cycle to repeat (22). With these cycles altered, the largest terrestrial carbon sink loses its potential. And with its potential lost, the system becomes a positive feedback loop. As climate change impacts the Taiga, it loses its carbon storage capacity. With more carbon in the atmosphere, climate change accelerates. And as climate change accelerates, the Taiga stores less carbon. Similarly, as surface temperatures increase, the biome’s snow and ice cover shrinks. As the white surface fades, albedo is lost and more heat is absorbed. This

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increase in heat leads to increased surface temperatures and consequently less snow cover. Essentially, there will be 4 major transformations to the boreal biome. The subarctic climate that helps define the boreal region today will become wetter, hotter and more seasonal. The biome will migrate north and to higher latitudes. The forest itself will shift to a more deciduous forest, changing the diversity and interactions of species. And the biome’s role in the carbon cycle and global albedo effect will diminish. Remembering the definition of a biome, one can safely say that these 4 transformations will change the biome itself. The flora and fauna that make up the community will change, the adaptations needed to survive in the biome will change, and the particular environmental condition will change. The beginnings of these transformations have already been observed but, like climate change itself, the consequences that stem from them will take time. Anthropogenic increases in carbon output are directly related to the changing climate. The consequential increase in temperatures, change in precipitation patterns, and shift in Earth’s oceans will introduce their own consequences. As if knocking dominos, we have pushed industry into the greenhouse effect. With the greenhouse effect in motion, warming surface temperatures and change in precipitation patterns are quick to follow. Domino felling domino and change inciting change; boreal forests are in a changing world.

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