Amazon fires are a major threat to the world’s largest rainforest, but we’re only just beginning to understand how fire spreads there.

NASA recently released a study that looked at understory fires burning in the Amazon rainforest between 1999 and 2010. Through satellite imagery, they found that 2.8 percent of the rainforest has been affected by these devastating undestory fires.

So, what makes these understory fires so bad? The understory of the rainforest is not easily visible from the air so satellite views used to be able to see only so much. These fires also burn incredibly slowly so it’s hard to track their progress and just how much they burn.

That being said, NASA says that the trees in the rainforest have not yet adapted to fire. That means the trees affected by fire can not shrug off the damage caused and end up dying. The researchers estimate that as many as 50 percent of all trees affected by understory fires end up dying.

Thankfully, deforestation and understory fires are not related whatsoever. NASA originally thought that might be the case, but they found that forests next to those that had been cleared had the lowest rates of fire. Both are still detrimental to the rainforest, but it would have been even more disastrous if deforestation and fires had been related.

The researchers believe they may be able to predict areas of the forest that are more likely to catch fire in the future. They will now focus their efforts on this to help prevent more destruction.