One-third of global forest loss has been caused by wildfires

Changing climate, with associated increasing global temperatures and more severe droughts in places, has created favorable conditions for wildfires over the past few decades. Large-scale fires in Australia, Brazil and California in the past two years have highlighted this phenomenon and drawn the world’s attention to the plight of forests around the world.  

Studies have shown changing fire dynamics across the globe due to both changes in climate and changes in land use by humans. However, when scientists try to assess the global trends in fire-related forest loss, they are faced by a lack of globally consistent methodology in measuring this variable, as well as the problem that some satellite maps used have a course resolution (375 m for VIIRS and 1 km for MODIS) that does not allow discrimination between forest wildfires and burns on agricultural lands at the forest fringes. 

“In the case of the Amazonian fires of 2019, there was no clear information on what exactly was burning: forests or previously deforested areas that had been converted to pasture and cropland,” explained Dr Alexandra Tyukavina, of the University of Maryland. “Even I, as a geographer, was terrified reading all the headlines that seemed to imply that the last patch of the Amazonian rainforest was on fire, which was not true.”

No high-resolution global satellite-based assessment of forest loss due to fire, employing consistent definitions and methods across biomes, has been available to date. In order to address this information gap, Tyukavina and her colleagues have developed the first ever 30m resolution (a 30 meter pixel represents a square patch of the land with a 30m side) global map of forest loss due to wildfires between 2001 and 2019. The study was published recently in Frontiers in Remote Sensing.

In their study, they defined forest loss as the removal of woody vegetation over five meters in height, and distinguished between forest loss due to fires and forest loss due to other factors such as agriculture (mechanical clearing of forests), floods, and hurricanes. They report the annual estimates of forest loss due to fire, and their trend between 2001 and 2019, globally and by climate domain within each region/continent. In addition, they analyzed trends in fire loss in tropical primary forests separately, because these forests have a high biodiversity and ecosystem service value.

“We have been producing the global forest loss map and updating it annually since 2013, but we did not attribute drivers of forest loss. This means that we did not know what exactly happened to forests (fire or mechanical removal) and we didn’t know whether this forest loss was temporary (for example, due to slash-and-burn farming) or long-term (deforestation),” said Tyukavina.

The new map with its more refined scale, showed that the proportion of global forest loss due to fires between 2001 and 2019 is 26 to 29 percent, which is higher than what was previously estimated. It showed relatively consistent increases in wildfires across the globe, with boreal forests having the highest proportion of forest loss (69–73 percent), followed by subtropical forests (19–22 percent), temperate forests (17–21 percent), and tropical forests (6–9 percent).

The map shows that the area of fire-related forest loss is increasing globally, but particularly within the tropical primary forests of Africa and Latin America.  Primary forests are forests in their ‘final form’; fully grown, dense, and bursting with biodiversity. They are extremely important for the environment due to their biodiversity richness and the ecosystem services they provide.

“The map is annual, and not near-real-time, so it won’t help monitoring forest fires in real time but will be useful as a historic baseline regarding the rates of forest loss due to fire,” said Tyukavina.

The researchers propose to use the map as a tool for forest management, policy and conservation program development, and climate modeling. They state that understanding more about the exact drivers of forest fires will help from the standpoint of carbon accounting and land management.

“Our new map is a good indicator of where the fires resulting in the loss of forest canopy have happened in the last two decades, and could help guide future finer-detail national, regional and local-scale studies, or tune coarser-scale global models,” concluded Tyukavina.

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By Alison Bosman, Earth.com Staff Writer