Earth has roughly 3.04 trillion trees, which is nearly eight times the number of stars in the Milky Way.

A comprehensive study published in the journal Nature in 2015 provided the most accurate census of Earth's trees to date. Led by Thomas Crowther, then a postdoctoral fellow at the Yale School of Forestry and Environmental Studies, the research team combined satellite imagery with over 429,000 ground-based measurements. This dual approach allowed them to map tree density at a square-kilometer level across the entire globe.Before this study, the global tree population was estimated at only 400 billion. The new data revealed that the actual number is approximately 3.04 trillion, which drastically changed our understanding of the planet's carbon cycle. By comparison, NASA estimates that the Milky Way galaxy contains between 100 billion and 400 billion stars. This means there are roughly 7 to 30 trees on Earth for every single star in our galaxy.The study also highlighted that the highest tree densities are found in the boreal forests of the sub-arctic regions, including Russia, Scandinavia, and North America. These cold-climate forests are more tightly packed than tropical or temperate forests. However, the researchers also warned that humans have cut down nearly half of the world's trees since the start of civilization, with an estimated 15 billion trees lost every year due to deforestation and land-use changes.