D4.3.3 Change from net carbon accumulation to net loss in boreal forests Notes

Boreal Forests: A Carbon Sink on the Brink

1. Boreal forests, also known as the taiga, are one of the largest terrestrial ecosystems on Earth.
2. They play a crucial role in carbon sequestration, storing vast amounts of carbon in their trees and soil.
3. However, climate change is pushing these forests toward a tipping point, where they shift from being a net carbon sink to a net carbon source.

Warmer Temperatures and Decreased Snowfall

1. Climate change is causing warmer temperatures and reduced winter snowfall in boreal regions.
2. These changes have cascading effects on the ecosystem:
   1. Increased Drought: Less snowfall means reduced water availability during the growing season, leading to drought conditions.
   2. Reduced Primary Production: Drought stress weakens trees, reducing their ability to photosynthesize and store carbon.
   3. Forest Browning: Trees lose their vitality, turning brown as they struggle to survive.

The Role of Forest Fires

1. Warmer and drier conditions increase the frequency and intensity of forest fires.
2. These fires have devastating effects on carbon storage:
   1. Legacy Carbon Combustion: Fires release carbon stored in trees and deep soil layers, including peat, which can burn for extended periods.
   2. Loss of Vegetation: The destruction of trees reduces the forest's ability to absorb carbon in the future.

A Tipping Point: Net Carbon Loss

The combination of drought, reduced primary production, and increased fires pushes boreal forests toward a tipping point:

1. Net Carbon Source: Instead of absorbing carbon, the forest releases more carbon than it stores.
2. Positive Feedback Loop: More carbon in the atmosphere accelerates warming, further increasing drought and fire risks.

From Carbon Sink to Carbon Source

1. In a healthy boreal forest, trees and vegetation absorb more carbon than they release, acting as a carbon sink.
2. However, with the onset of increased drought, forest browning, and wildfires, the forest begins to release more carbon than it can absorb.
3. This shift results in a net carbon loss, as carbon is released into the atmosphere both through increased respiration from stressed vegetation and combustion during wildfires.

Why Does This Matter?

The shift from net carbon accumulation to net loss in boreal forests has global implications:

1. Accelerated Climate Change: The release of stored carbon amplifies global warming.
2. Biodiversity Loss: Species adapted to cold, stable environments face increased threats from habitat destruction.
3. Economic Impacts: Forest-dependent communities suffer from the loss of resources and increased fire management costs.

What Can Be Done?

Addressing this tipping point requires urgent action:

1. Fire Management: Implementing controlled burns and firebreaks to reduce the risk of catastrophic fires.
2. Restoration Efforts: Replanting trees and restoring degraded areas to enhance carbon sequestration.
3. Global Cooperation: Reducing greenhouse gas emissions to mitigate the root causes of climate change.