NASA Discovers Unmapped Wildfire Destroying Amazon Rainforest

The Amazon Rainforest is one of the most diverse ecosystems on the planet. Now, though, NASA has revealed that something else is threatening the rainforest. A previously unmapped type of wildfire is responsible for destroying several times more forest than has been lost through deforestation in recent years.

NASA satellites monitor the rainforests in South America. Yet fires below the forest treetops, also known as "understory fires," have been hidden from NASA's gaze. Now, though, the agency has developed a new technique that allows them to see the damage that these types of fires cause. The findings are disheartening.

"Amazon forests are quite vulnerable to fire, given the frequency of ignitions for deforestation and land management at the forest frontier, but we've never known the regional extent or frequency of these understory fires," said Doug Morton of NASA's Goddard Space Flight Center in a news release.

Fires can burn quickly in the Amazon's savanna areas, spreading up to 330 feet per minute. Grasses and shrubs typically survive low-intensity surface fires. However, the fires in the rainforest's understory areas are quite different. Flames only reach a few feet high, but they can burn for many weeks at a time. Yet while grasses in the savanna areas are adapted to fire, the trees in the understory areas are not. This means that understory fires can destroy trees at a rapid pace.

In order to actually view these understory fires, the researchers used observations from early in the dry season collected on NASA's Terra satellite. They tracked both the timing and the recovery from fire damage. This allowed them to see exactly how much of an impact understory fires were having on the ecosystem.

After analyzing the data, the researchers made some surprising finds. They discovered that between 1999 and 2010, more than 33,000 square miles were burned by understory fires. That's a whopping 2.8 percent of the forest. While the fires seemed to be heating up, though, it didn't seem to be the result of deforestation.

"You would think that deforestation activity would significantly increase the risk of fires in the adjacent forested area because deforestation fires are massive, towering infernos," said Morton. "You make a bonfire that is a square kilometer in size, throwing ash and live cinders and preheating the adjacent forest. Why didn't we have more understory fires in 2003 and 2004, when deforestation rates were so high?"

It turns out that climate is the answer. Frequent understory fire activity actually coincides with low nighttime humidity. That means when the climate is drier, forest fires are more likely to spark.

The findings highlight the importance of considering understory fires when mapping the disappearance of the Amazon rainforest. In addition, is shows how these fires can be a significant source of carbon release, which means climate models should take them into account.

The findings are published in Philosophical Transactions of the Royal Society B.