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Sunday, November 30, 2008

Boreal North America

A mature spruce stand near
Delta Junction, Alaska

The North American boreal forest is an integral part of our global ecosystem and an important influence on the global cycling of energy, carbon and water. Over the past 30 years, global boreal forests have experienced a significant amount of warming and drying which, if trends continue as predicted, are likely to induce feedbacks that may further influence global climate. The goal of our North American Boreal Carbon program is to quantify the magnitude and variability of carbon exchange, and to assess the mechanisms by which fire disturbance influences these processes. By synthesizing results from direct field measurements, satellite remote sensing and ecosystem modeling, we study the processes driving changes in the boreal forest in order to inform assessments and predictions of how those changes will be expressed under a future climate regime.


Why Study Boreal Forests?

  • Coverage - Boreal forests cover approximately 14.5% of the earth's land surface. Learn More »
  • Carbon Storage - The great expanse and large quantity of carbon contained in vegetation and soils (particularly peat) make the boreal biome the world's largest terrestrial carbon reservoir. Learn More »
  • Changing Climate - At high latitudes in North America, substantial warming and drying has occurred, and this trend is predicted to continue. Increased temperatures in the boreal region release large quantities of carbon previously immobilized in the cold and frozen soils. The large quantity of carbon contained in the cold and frozen soils of the boreal biome is susceptible to mobilization under a changing climate system. Learn More »
  • Fire and Regrowth - Warming and drying associated with climate change increase the frequency and intensity of the boreal fire regime, and lead to changes in vegetation composition and the carbon cycle. Learn More »

Coverage of Boreal Forests

MODIS Tree Cover data displaying the forests of North America and Eurasia. Percent tree cover increases as colors become darker.

It is estimated that boreal forests and woodlands cover approximately 14.5% of the earth's land surface, comprising an area of nearly 16 million square kilometers (5.7 million square miles) – or about the size of the conterminous United States. The boreal region forms a circumpolar band throughout the northern hemisphere, extending through Russia, Northern Europe, Canada, and Alaska (see image, right). The southern limit of the boreal forest biome is not a distinctly defined boundary, but generally varies between 50° and 60°N latitude, although in Siberia it dips as far south as 45°N. The North American boreal region makes up approximately one third of the global boreal biome, and thus constitutes a significant component of the boreal carbon pool.


Carbon Storage in Boreal Forests

The boreal region covers just under 15% of the global land surface, but contains over 30% of all carbon contained in the terrestrial biome. This is largely due to the disproportionate amount of carbon held in boreal soils compared to other forest biomes. In general, the amount of carbon stored in forest soils is controlled by the rate of supply and release of carbon. Carbon is supplied to the soil through litterfall, fallen woody debris, and root mortality. This detritus is subsequently decomposed through various microbial pathways and the carbon is released to the atmosphere.



Comparison of Carbon Storage in Boreal, Temperate, and Tropical Forests

Biome Area (x 106 ha) Soil Carbon (Pg) Plant Biomass Carbon (Pg) Total Carbon (Pg)
Boreal Forest 1,509 625 78 703
Tropical forest 1,756 216 159 375
Temperate forest 1,040 100 21 121
Based on Kasischke, 2000

(One Pg [petagram]=one billion metric tonnes or one trillion kg)


In boreal regions, extremely low temperatures promote the formation of cold and frozen soils called permafrost. The cold temperatures within these soils reduce decomposition rates, thereby leading to the development of deep organic soils that may be hundreds of years old. These cold, often saturated or frozen organic soils release relatively little CO2 to the atmosphere through microbial respiration, although large amounts may be rapidly released by increasingly frequent forest fires, which also generate deep soil thawing once the insulating blanket of moss and peat is removed.

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