Primary Forests: Boreal, Temperate, Tropical

primary forests: boreal, temperate, and tropical
Info sheet & references
Info sheet & references
Info sheet & references
thumbnail image of Primary Boreal Forests pdf thumbnail image of Primary Temperate Forests pdf thumbnail image of Primary Tropical Forests pdf
thumbnail image of Primary Boreal Forests references pdf
Research area

Primary Boreal Forests

Primary boreal forests provide critical stores of carbon, biodiversity and freshwater

Boreal forests are home to 481 Million hectares of remaining primary forest, or 41% of the global total


Boreal forests store about 65% of the world’s forest carbon, which is mostly held within the soils.

  • The cold, wet, environment slows decomposition on the forest floor, leading to thick layers of moss and litter, and soils that can be meters deep storing ~85% of the ecosystem’s carbon. Due to climate change, these regions are becoming warmer and drier, meaning that the amount of carbon these ecosystems can store will likely be lower in the future.
  • Permafrost is soil that remains frozen throughout the year, preventing decomposition and storing large quantities of carbon. In a warming climate, permafrost will thaw, emitting methane and carbon dioxide.
  • Peat is partially decayed vegetation often found in the fens and bogs of the boreal forest, where the water-saturated soils prevent full decomposition, and stores 270 billion tonnes of carbon across the boreal forest.
  • Carbon storage within the soils of the boreal forest has a turnover rate of approximately 50 years, which is more than twice as long as that in temperate or tropical forests.
  • Fire is a natural part of this ecosystem and is necessary for the regeneration of several important tree species. However, climate change is leading to higher frequency and severity of these fires.
  • Clear-cut logging does not mimic wildfire. Fires do not combust tree boles, and the resulting dead standing trees and woody debris are longer-lived than most sawn timber products by at least a factor of two.

CARBON STORED [in billion tonnes]: 1,042
TOTAL BOREAL FOREST carbon = more carbon than is currently stored in the atmosphere and twice as large as all anthropogenic emissions since 1870
CARBON STORED [tonnes C ha-1]
vegetation: 47–142
soils: 125–812
peat: 110–1,213

Below ground: 912    Above ground: 130


Big, Old Trees

Large trees are critical to maintaining biodiversity, and are being lost due to harvesting and other anthropogenic impacts.

  • Southern boreal forests typically have trees 15–30 m high, while northern boreal forests have stunted trees usually 3–15 m high.
  • Old trees are critical for the growth and abundance of epiphytic lichens on their branches, which can decrease by a factor of 6 in managed forests.
  • Old, dead trees, both standing and on the ground, provide diverse habitats that are important for many species of birds, fungi and insects.
  • Logging and other anthropogenic disturbances homogenize the landscape, leading to an abundance of young forests and a scarcity of older forests, while removing much of the dead wood, and render the forest vulnerable to human-ignited fires.



The diverse ecosystems, flora and fauna within the boreal forest, contribute to the ecosystem services this biome provides.

  • US$703 billion of services per year in Canada alone.
  • 60% of the world’s remaining surface freshwater is stored within the boreal forest, and the wetlands purify this water, filtering out contaminants.
  • Provides important breeding ground for birds from further south, and important for almost half of all North America’s bird species.
  • Maintaining biodiversity leads to higher levels of ecosystem services such as carbon storage, berry production and game populations.
  • Many indigenous communities are dependent on the ecological integrity of old growth boreal forests for medicinal plants, cultural practices and traditional livelihoods.
  • These ecosystem services are likely at risk under the warming climate.

Primary Temperate Forests

Harbor unique biodiversity and Ecosystem services, including climate regulation

Temperate forests are home to 108 Million hectares of remaining primary forest, or 9% of the global total, highlighting the urgency of protecting what’s left


Primary temperate forests sequester and store vast amounts of atmospheric carbon in living and dead biomass and soil organic matter, holding on to it for centuries.

  • The world’s highest known biomass (above ground live + dead) of 187 kg/m² is in Victorian Mountain Ash forests.
  • Unlogged forests store ~40%-55% more carbon than logged forests.
  • When old forests are cut down, two-thirds or more of their stored carbon is released to the atmosphere as a global warming pollutant from combustion and decomposition on-site and emissions from the wood-product manufacturing and distribution chain.
  • Logging emissions are not “offset” by planting trees or storing carbon in short-lived wood products.
  • Large, old trees sequester carbon at rates 3x that of smaller trees.
  • Large trees (>1 m diameter) contribute 76% of the total biomass in old-growth forests, but only 43% of tree numbers.
  • Longevity of carbon stocks determines the degree of climate benefit.
  • Trees should be allowed to grow old to maximize climate, water, and biodiversity benefits.
  • Clear-cut logging does not mimic wildfire. Fires do not combust tree boles, and the resulting dead standing trees and woody debris are longer-lived than most sawn timber products by at least a factor of two.

CARBON STORED [in billion tonnes]: 119
TOTAL TEMPERATE FOREST CARBON = equivalent to global CO₂ emissions from 2005–2017
CARBON STORED [tonnes C ha-1]
vegetation: 147–377
soils: 83–268
root+dead vegetation: 102–265

Above ground: 47    Below ground: 72


Big, Old Trees

Loss of big, old trees is a global concern as fewer of them, and the primary and intact forest landscapes that harbor them, remain due to logging and other threats.

  • Trees can tower to >100 meters (coast redwood, mountain ash) with a base circumference of >9 meters (giant sequoia, New Zealand Kauri tree).
  • Trees can live for over a thousand years, continuously accumulating and storing carbon, while helping to regulate the climate and hydrological cycle through forest-atmospheric feedbacks.
  • Dead big trees provide shade and moisture for seedlings, nest sites for birds and mammals, serve as biological legacies jumpstarting forest renewal, and provide cultural and spiritual connections for people.
  • Old forests, especially in floodplain areas, buffer human communities from floods and droughts.
  • Old trees are irreplaceable in human lifetimes and need to be protected from logging.
  • Old growth wet temperate forests are far more resistant to drought and fire than logged forests.



Primary wet temperate forests (deciduous, evergreen, broadleaf, conifer, mixed) harbor diverse communities that experience distinct seasonal changes affecting productivity, ecosystem services, and migratory species, especially birds.

  • Primary forests include both exceptionally biodiverse and productive older forests and complex early seral forests created by natural disturbance regimes ranging in frequency and intensity, including intense events that kill most of the trees in an area.
  • Lichen richness is among the highest of any forested ecosystem.
  • Forest carnivore assemblages and complex food-web dynamics are fully present and functional.
  • Keystone species, like anadromous salmon, connect terrestrial and marine environments through nutrient cycling of spawned-out salmon carcasses.
  • Small mammals feed on below-ground fungi, aiding in spore dispersal of mycorrhizae, which allow plants to take up nutrients efficiently.
  • Myriad ecosystem services such as nutrient cycling, soil development, climate regulation, and water filtration.
  • Temperate forests cover roughly one-third of original extent vs. 45-65% for tropical and boreal forests, respectively.

Primary Tropical Forests

Ecosystem integrity of primary tropical forests is critical for biodiversity and carbon


  • Tropical forests store 471 Pg C, of which roughly 50% is found in tropical primary forests.
  • Forest growth drives carbon sequestration, but emissions caused by deforestation and degradation take decades to centuries to reverse.
  • Degradation and deforestation of tropical forests for alternative land uses, such as agriculture and pasture, emits 4.7 billion tonnes of carbon each year.
  • Tropical production forests store on average 35% less carbon than tropical primary forests of the same type.

CARBON STORED [in billion tonnes]: 471
TOTAL TROPICAL FOREST carbon = greater than all carbon emissions from fossil fuels since 1750
CARBON STORED [tonnes C ha-1]
vegetation: 240
soils: 50+

Above ground: 320    Below ground: 151


Big, Old Trees

Big, old trees occur at low densities per hectare but are essential to the health of a primary tropical forest.

  • Store up to half of the biomass carbon in a forest.
  • Live for centuries, continuously accumulating carbon throughout their lifetimes.
  • Provide essential habitat for biodiversity acting as ecological anchors within the food and community webs that are the processes producing forest resilience.
  • Create a stable forest interior environment that is protected from extreme weather conditions.
  • Big trees need to be protected—they are quickly destroyed by logging but take centuries to regrow.



Native animals, plants, trees, fungi and microbes interact to create stable and enduring primary forests. Primary tropical forests are irreplaceable for biodiversity. They protect about two thirds of all terrestrial plant and animal species, many of which do not survive in degraded forests.

  • Mammal, bird, reptile and insect seed dispersers and pollinators ensure trees, including long-lived, hardwood species, “replant themselves” and renew the forest.
  • Forest fauna and flora drive efficient nutrient and water cycles, maintaining healthy forest growth.
  • The closed forest canopy creates an interior microclimate sheltering the understory and maintaining moist, shady and cool conditions.
  • Water retained below the canopy stimulates rapid and dense tree and other vegetation growth.
  • The canopy transpires water, driving convection, which in turn can generate regional cloud cover and rainfall.
  • All of these attributes combine to create primary forest stability and resilience to threats from diseases, invasive plants, feral animals, drought and fire.
  • These attributes also enhance ecosystem adaptive capacity to climate change and other stress.

In partnership with


Australian Rainforest Conservation Society