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Water loss and plant biology: The demise of boreal peatlands

Boreal forests stretch across the high northern latitudes of Europe, Asia, and North America. These forests are major carbon sinks, sequestering carbon in their above-ground biomass and below-ground in the forest soils. The boreal ecosystem also contains vast areas of peatlands.  The ability of boreal ecosystems to sequester carbon is very dependent on retaining high levels of moisture within the plants and soils. The moisture deters or retards fires that release carbon back into the atmosphere. But peatlands and forests have very different moisture retention capacities, and the peatlands are more vulnerable to water loss and damage from global warming. 

Boreal forests exist where freezing temperatures occur for six to eight months of the year. These forests are defined by trees that reach a minimum height of five meters and develop a canopy cover that is at least ten percent of the forest area. Peatlands, however, are dominated by lakes, bogs, and fens. These wetlands contain thick layers of living and dead moss, thus making them excellent carbon sinks.

However, warming associated with climate change poses a variety of threats to the boreal ecosystems. Warmer climates bring dryer air that sucks more moisture from the forests and peatlands. The ability of each local environment (forest or peatland) to retain moisture is dependent on the plants growing there.

Vascular versus nonvascular

Moss, liverwort, and hornwort are all nonvascular plants. These were the first species of plants to creep out of the ocean 470 million years ago during the Ordovician period and carve out an ecological niche on land. It was not until the ensuing Silurian period that vascular, tree-like plants arrived on the scene. 

The nonvascular plants provide low creeping vegetation. They are small in size since their growth is limited by poor internal transport of water, gases, and nutrients. The needs of these nonvascular plants are well met by the wet conditions of the peatlands. Vascular plants, however, are needed to develop forested landscapes. The vascular plants are much more efficient at transporting and storing water and nutrients. This efficiency, therefore, allows them to grow taller and live longer. 

This difference between vascular and nonvascular plants dramatically affects their response to warmer, dryer conditions. Trees use microscopic pores in their leaves to take in carbon dioxide and breathe out water and oxygen. So, their vascular system lets them store lots of water, and when dry conditions arrive, they close their leaf pores to reduce water loss. Moss, however, is nonvascular and small in size. Its water storage capacity is minimal, and thus the plant quickly desiccates under dry conditions. 

Natural firebreaks disappear

Boreal forests are not exempt from wildfires. But, peatlands interspersed among the woodlands provide a level of protection. Because these wetlands serve as natural firebreaks, they retard the spread of wildfires, thus limiting the damage. However, this advantage may disappear as the climate warms. 

As the peatlands dry out, decomposition of their stored carbon will accelerate.  The resulting larger volumes of dried organic material in the peatlands will alter them from firebreaks into zones that propagate the spread of wildfires. The natural balance of the boreal ecosystem will change as water loss accelerates, and its ability to act as a carbon sink will be diminished.


Forests as a pathway for terrestrial carbon sequestration (Source: ArcheanWeb) –  Also:

Tongass National Forest: The good, the better, and the beautiful (Source: ArcheanWeb) –  Also:


Water loss in northern peatlands threatens to intensify fires, global warming (Source: McMaster University) –  Also:

About Boreal Forests (Source: International Boreal Forest Research Association) –  Also:Feature Image: Impressions Of A Boreal Forest (Modified) – By Kerbla Edzerdla – Imported from 500px (archived version) by the Archive Team. (detail page), CC BY 3.0,

William House
William is an earth scientist and writer with an interest in providing the science "backstory" for breaking environmental, earth science, and climate change news.