Charcoal remains after fires accelerate CO2 emissions in boreal forests

A study has recently revealed that charcoal remains after a forest fire may help decompose fine roots in the soil and consequently accelerate CO2 emissions in boreal forests.

Burning trees in forest fires naturally causes the emission of CO2, but little is known about the extent to which fire-derived charcoal influences ecosystem processes, such as soil organic matter decomposition.

Author Makoto Kobayashi from Hokkaido University said that the study has provided the first field evidence that fire-derived charcoal might accelerate the decomposition of fine larch roots and consequently CO2 emissions from boreal forests.

Boreal forests are a huge carbon sink. The fine roots, not only the leaves, stems and branches of trees, largely contribute to carbon accumulation.

Senior Researcher Semyon Bryanin from Russian Academy of Science and Kobayashi performed field litterbag experiments over 515 days, incubating fine larch roots with varying concentrations of charcoal in the soil.

Mass loss of fine roots were measured in each of four conditions over nearly two years: control (no charcoal); mean charcoal content measured in the field; twice the mean charcoal content measured in the field; and charcoal content equal to the maximum concentration in the field.

The results revealed that charcoal had little effect on the decomposition of fine roots right after they were buried in soil.

But at the end of the experiment, the loss of root mass in samples incubated with higher concentrations of charcoal was greater (double content: 40 per cent; maximum content: 42 per cent) than in the control (30 per cent) and the average content conditions (27 per cent).

The findings likely will help predict future changes in CO2 concentration in the atmosphere should more forest fires be triggered by global warming and human activities.