Earth has more trees than the Milky Way has stars

Earth has more trees than the Milky Way has stars. A 2015 study in Nature estimated that the planet holds about 3.04 trillion trees. NASA says our galaxy probably contains 100 to 400 billion stars.

Where the tree number comes from

A team led by T. W. Crowther built what the paper calls "the first spatially continuous map of forest tree density at a global scale." Their map, in the paper's words, "reveals that the global number of trees is approximately 3.04 trillion, an order of magnitude higher than the previous estimate."

The paper splits that total by region:

• About 1.30 trillion trees in tropical and subtropical forests.
• About 0.74 trillion in boreal regions, the cold northern forests.
• About 0.66 trillion in temperate regions.

Those regional figures come from the corrected version. In December 2015, Nature published a correction: the tropical figure should read 1.30 trillion (not 1.39) and the temperate figure 0.66 trillion (not 0.61). The 3.04 trillion total did not change.

And the stars?

Nobody can count the Milky Way's stars one by one from inside it, so astronomers estimate. NASA's stars page says "our Milky Way alone contains more than 100 billion." Another NASA page puts it at "100 to 400 billion stars."

So the comparison holds across the whole range:

• At 100 billion stars, trees outnumber them about 30 to 1.
• At 400 billion stars, trees still outnumber them about 7.6 to 1.

Both ratios are our math: 3.04 trillion divided by each star estimate.

The part that is less fun

The same study looked at what people have done to the count. Based on its tree densities, the team estimated that "over 15 billion trees are cut down each year, and the global number of trees has fallen by approximately 46% since the start of human civilization."

The limits

• Both numbers are estimates. The tree count is modelled from a map, and the star count depends on assumptions about the mass of an average star.
• The tree count is from 2015. Forests have changed since then, and this paper has not been redone with newer data.
• The ratio changes a lot depending on the star estimate you pick, which is why we give a range.

Sources

• Crowther, T. W., et al. (2015). Mapping tree density at a global scale. Nature, 525, 201 to 205. Nature abstract
• Corrigendum: Mapping tree density at a global scale. Nature, 532, 268 (2016). Nature correction
• NASA Science, Stars. science.nasa.gov/universe/stars
• NASA Science, Our Milky Way Galaxy: How Big is Space? science.nasa.gov