Let it burn! Are the greenhouse gas emissions following prescribed burning in Nordic boreal forests a threat to climate change objectives?

This post-doctoral project is funded by the Maj and Tor Nessling Foundation (2025-2027)

The ideal forest

The forests of Fennoscandia are world-renowned for their careful and intensive management practices where trees stand tall, straight, and uniform. Despite a harsh climate and soils that are often poor, forests in Fennoscandia are productive, due to a careful schedule of planting, thinning, and fertilization that ensures optimized growth and an excellent final product with little waste. However, there has been a price to pay for replacing natural processes with calculated control, biodiversity is declining in these forests and threatened species are growing. To solve this, more than just parks are reserves are needed. Instead, we have to bring back ancient processes that once dominated the landscape: forest fire.

A mature Scots pine stand typical of dry sites with sandy soils in Finland. Evidence of past fire can be found in this forest, which is located in a protected area. (N. Kokkonen photo)

Fire and loss

Fires are often considered destructive threats that destroy things that we value. This is why such effective fire suppression systems have been developed. But forest fires are natural and even necessary for many plants, animals, insects, and fungi. Without fire, many species that depend on this process, i.e. pyrophilic species, are unable to survive. Currently in Finland, there are 108 threatened species that are associated with fire habitats. 2 have been extirpated and 2 are officially endangered. This needs to change.

Evidence of a fire history can often be found in old pine forests where blackened fire scars and charcoal buried below the moss give clues about what has happened. (N. Kokkonen photo)

Controlled re-introduction

There is now global recognition from international and national governments, non-profit organizations, and certification schemes that fire must come back to the Fennoscandian boreal forest. The aim of this is to increase biodiversity (ecosystem integrity) and restore natural processes to the forest. Prescribed burning, i.e. the careful use of fire by trained professionals, is being used in both protected areas and the forest industry in an effort to increase naturalness across the landscape. These fires are often planned to mimic the low-burning fires that characteristic to the region, where moss, plants, and downed wood are burnt, but most green trees survive. Despite making forests more natural, these fires also have a drawback. They release carbon dioxide, methane, and other greenhouse gasses that are known to cause climate change.

Restoration burning, a type of prescribed burning, being applied to a previously intensively managed forest as it transitions to become a protected area. (M. Rebiffé photo)

Forest fire and carbon

Without fire, the boreal forest stores carbon in the trees, plants, and most importantly soils. This is because plant photosynthesis gains more carbon than what is lost through decomposition in this cool and moist climate meaning a slow accumulation of carbon-rich materials. However, when a fire burns forest fuels it releases massive amounts of carbon to the atmosphere as greenhouse gasses and ash particles. Fuels consist of materials that contains carbon such as wood, plants, and even peat. The long-term impact of fire on carbon storage can be even more than what is lost during burning. Plants die and no longer photosynthesize meaning that they don't take carbon up from the atmosphere. Special soil bacteria that consume methane from the air (i.e. methanotrophs) no longer function the same after fire. This new balance can last for decades as the forest slowly recovers.

Some plants can regrow quickly after fire and start photosynthesizing. For others, it can take decades. Charred material covers the forest floor and does not rot easily meaning it is a long-lasting sign of fire. (N. Kokkonen photo)