Leeds Ecosystem, Atmosphere & Forest (LEAF) Centre

Fire emissions enhance photosynthesis across Amazon Basin

July 3, 2015

A new study from LEAF scientists indicates that particles generated by biomass burning in the Amazon increase the productivity of the remaining forest.

Hazy air during biomass burning season

Fires in forests can occur naturally but are often started deliberately by humans. The main reason for this is to clear the land of trees so that it may be used for farming, and fires can be used again and again on the same land to prevent the trees from growing back.

When forests burn, the fires release both gases and particles into the atmosphere. This new study investigated how the particles that are emitted affect the amount of the Sun’s radiation that makes it through the atmosphere and reaches the trees below.

Particles generated by fires can scatter incoming sunlight, changing its path to the surface. This is important because parts of the tree canopy that would otherwise have been shaded become able to receive light from the sun when it arrives at a different angle.

LEAF researchers used a combination of computer simulations to explore the implications of this. They found that by increasing the amount of sunlight received by the plants, the presence of the fire particles caused an overall increase in photosynthesis and the productivity of the forest canopy. This increase in productivity means that the plants are able to take in, and store, more carbon.

Lead author of the study, Dr Alex Rap explains: “The small particles emitted from Amazon fires make light more diffuse and the forests respond by entering a more efficient photosynthesis regime and absorbing additional carbon.”

Smoke plume from biomass burning

Of course, when forests burn, carbon is emitted directly into the atmosphere. This study found that across the Amazon basin, the increased carbon storage resulting from enhanced productivity due to fire particles could be as much as 65% of the amount that is lost from the forest through direct emission.

“This extra carbon uptake offsets some of the original carbon emission from fires, and counteracts part of the effect of droughts. It also explains a fraction of the observed carbon sink across mature Amazonian forests”, added Dr. Rap.

By comparing to data collected from forest plots across the Amazon by the RAINFOR network, the new study concluded that increase in productivity was equivalent to between 8 and 16% of the observed carbon sink across mature Amazonian forests.

Read the full study here.

Post by Cat Scott – University of Leeds.