Each year our species cuts down 26 billion trees and only re-plants half of that. At this rate the Earth will run out of trees. At the moment, reforestation is done by hand planting, which is limiting the speed at which replanting can occur. Enter ex-NASA engineer Lauren Fletcher. Her team at BioCarbon Engineering plans to save the planet by mechanising the replanting process. A section of land will be mapped using automated drones to build an accurate 3D model of the terrain. Individual routes will then be planned and programmed into a small army of planting drones. Each planting drone carries a small bottle of pressurised air and a multitude of pre-germinated seeds. As the drone flies along its route it fires these seeds into the ground from a height of one to two metres. Each seed is covered with nutrient-filled hydrogel to provide a stable environment for the plant to grow in initially. Fletcher doesn’t pretend that this system is as good as hand-sowing—a human can plant a seed far more precisely with a higher success rate—but a drone can plant them faster and currently, time is of the essence.