In the age of Google Maps, it’s easy to assume that everything has been discovered, mapped, and made known. The zoomable satellite view is right there at our fingertips; even undersea topography is rendered on our screens.

Ironically, then, it was during a seabed mapping expedition in 2021 that divers discovered a pristine coral reef off the coast of Tahiti, “rose corals stretching as far as the eye could see,” as one of the divers described it. Also last year, an ocean survey in Antarctic waters stumbled across a staggering 60 million icefish nests, orders of magnitude larger than the largest colony of this clear-blooded fish previously known.

To happen upon two such abundant ecosystems by chance offers encouragement that parts of nature are still thriving and that there’s a world to protect from pollution, degradation, and climate change.

These discoveries also reveal how incomplete our knowledge of the natural world remains. Not just in the ocean deep: even on terra firma, unknowns abound. For instance, although trees are some of the largest and most wide-spread life forms, we don’t know exactly how many species of them exist.

Now, a new study offers more precision. “Until today, our data regarding wide areas of the planet was very limited and based on field-observation and lists of species covering different areas,” explained the study’s first author, Roberto Cazzolla Gatti, from the University of Bologna.

The researchers used large global datasets to map millions of individual trees and tens of thousands of species. “We then performed complex statistical analyses by using artificial intelligence and supercomputers to estimate that there are still 9,000 unknown tree species on Earth, most of them very rare,” said Gatti. In total, the study estimates there are roughly 73,000 tree species on Earth, about 14% more species than previously known.

“This global dataset is so exciting because it allows us to uncover fundamental features of our planet, which are so important in our efforts to protect biodiversity,” said study co-author Tom Crowther, from ETH Zurich.

The study shows that almost half of the unknown tree species are concentrated in South America, and nearly a third of all undiscovered tree species have very low populations and aren’t widespread. As a result, they’re especially vulnerable to human-driven deforestation, fires, and climate change – which threaten the very possibility of discovering new species. Instead, what we may see are ripple effects from losing rare trees, finding the absence of these species through negative consequences for their ecosystems. These losses can also influence the climate, because forests and the biodiversity they support are such vital allies for limiting the severity of global warming.

Preserving the unknown is its own challenge. How do we protect a tree we don’t know exists? Or coral reef? Or a polar fish colony? Discovery and conservation go hand-in-hand: better understanding our planet better equips us to protect it. Meanwhile, halting our current degradation of nature offers more chances to catalog new species and even come across wondrous whole ecosystems.