Scientists deploy all sorts of fancy metrics to determine how much biodiversity they find in a forest. The Shannon Diversity Index is based on the number of species and the size of their populations. The Structural Complexity Index relies on the types of trees, their sizes and distribution. The Acoustic Complexity Index uses the variability in bird songs in audio recordings.

But there might be a simpler—if less rigorous—way to gauge how rich life is. Just show photos to someone with no special training at all.

It turns out that even city-dwellers are tuned to the natural world in ways that enables them to accurately distinguish between more and less biodiverse forests based simply on photos or sound recordings, according to new research in the journal People and Nature.

The findings help shed light on how people perceive natural environments, and the underpinnings of links between people’s mental wellbeing and their experience of biodiversity.

“Because it’s suspected that perceived biodiversity translates into mental health benefits, it’s important to identify what people perceive with regards to biodiversity, what the contribution of the different senses could be,” said Kevin Rozario, a scientist at the German Centre for Integrative Biodiversity Research.

In other words, if people key into certain aspects of biodiversity and that makes them feel better, maybe that holds clues both to our mental health and to what kind of biodiversity matters most for it.

To test whether people can intuitively grasp biodiversity, Rozario and colleagues showed 57 photos of a variety of European forests to 48 people. The participants then sorted the photos based on their perception of how biodiverse each was and offered descriptions of how they came up with their rankings. The scientists conducted a similar test with 16 audio recordings of birds in a forest.

The rating done by the people in the study correlated closely with more formal assessments of the levels of biodiversity shown in the images and recordings, the scientists found.

Then the researchers looked to see if they could come up with an official biodiversity index that matched with the results both from the participants and from the more scientific methods.

In the case of the photos, the one that worked best is what they dubbed the “Greenness Index”—based on how much green vegetation was present in a photo. People seemed to perceive more green as a sign of more biodiversity. At the same time, the photos with more green also ranked higher in biodiversity. That matches with research that has found more plant biodiversity generally coincides with more total plant matter, the authors noted.

With the audio recordings, the scientists found several metrics shared by amateurs in the study and pros alike, including the complexity and density of bird calls.

There are, however, limitations for people’s intuitive abilities to sense biodiversity. This study enabled people to compare different scenarios. However, previous work by some of the same scientists found that when people were taken to a spot in a forest and asked to estimate the richness of life there, they weren’t very good at it.

But there was still some good news even in that earlier research. People who thought they were in a more biodiverse place (even if they weren’t) reported feeling better.

Rozario, et. al. “Perceived biodiversity: Is what we measure also what we see and hear?” People and Nature. July 7, 2025.

Photo: CharukalpoStudio/Freepik