Are there more trees on Earth than stars in the Milky Way?

Look up on a clear night far from city lights and the sky seems endless. Look out of the window at a few trees in the street and it feels like no contest. Surely the galaxy wins? Surprisingly, it does not. If you want the bigger number, you are better off counting leaves than lights.

The short answer

Earth has roughly 3 trillion trees, according to a global count published in the journal Nature in September 2015. The Milky Way is usually estimated to contain about 100 billion stars, with some estimates reaching around 400 billion. Even taking the most generous star count, trees win by a factor of more than seven.

The real story

Before 2015, the best previous global estimate was about 400 billion trees. The new figure, from a Yale-led international team, was more than seven times higher. The researchers did not fly over every forest with a clipboard. They combined satellite imagery with ground-level forest inventories, measurements in which people actually count trees in sample plots, and used supercomputers to map tree density across the planet down to the square-kilometre level.

The result worked out to roughly 422 trees for every person on Earth. That sounds generous until you read the rest of the study. The team estimated that around 15 billion trees are cut down every year, and that the number of trees on the planet has fallen by almost half, roughly 46 percent, since humans began farming and building civilisations around 12,000 years ago.

So the twist cuts both ways. Yes, trees comfortably outnumber the stars of our galaxy, which is a lovely thing to know. But we also used to have nearly twice as many. The forests have been losing a slow-motion contest with axes, ploughs and bulldozers for thousands of years.

It is worth noting that star counts for the Milky Way are themselves rough. Counting every star individually is impossible, so astronomers work from general estimates, which is why the figure is given as a wide range. Even so, no mainstream estimate comes close to 3 trillion.

Why people get it wrong

Space feels infinite, and the night sky is a picture of countless points of light, so our instinct says the galaxy must hold the bigger number. Trees, by contrast, feel local and countable: a park here, a forest there. But that intuition ignores scale in both directions. The boreal forests, tropical rainforests and woodlands of Earth stretch across huge areas of land we rarely see. The galaxy is big, but it is mostly empty space. Earth is small, but it is very, very green.

The Sole’s verdict: “More trees than stars in the galaxy. So next time someone says you can’t see the forest for the trees, tell them the galaxy can’t either.”