Scientists estimate Earth is home to more than 3 trillion trees, but they're slowly disappearing by about 15 billion a year. Humans only plant about 9 billion each year.
But some groups are using drones to speed up forestation efforts.
Companies like BioCarbon Engineering use drones with onboard sensors that analyze terrain to find the best planting spots.
Once they find suitable land, the drones shoot seeds to the ground. BioCarbon Engineering's drones can carry up to 150 seeds at a time, and a pair of operators can seed an estimated 100,000 trees a day.
This makes planting by drone cost-efficient. Startup DroneSeed predicted one of its drones could plant 800 seeds in an hour, which would take a human all day.