You are a person. You are also an ecosystem. Your skin, gut, orifices, and organs are collectively home to trillions of microorganisms.

These microorganisms are not freeloaders. They contribute to your health in crucial ways, many of which science is only beginning to understand.

For example, we now know that the metabolites and other byproducts made by the microbes in your gut strongly influence the activity of your immune system. If some of these essential gut bacteria are missing or their populations are depleted — a condition GI experts refer to as dysbiosis — your immune system can misfire (or backfire) in devastating ways.

Inflammatory bowel disease, type 1 diabetes, rheumatoid arthritis, psoriasis, lupus, multiple sclerosis, thyroid disease, and allergies are just a sampling of the medical conditions that result from immune errancy, and that are driven in part by gut dysbiosis. All of these conditions were once rare, but their prevalence has surged in recent decades.

‘Our environments and how we interact with them dictates what gets into us, and that in turn dictates our health.’

Similarly, there’s mounting evidence linking gut dysbiosis to common mental and neurological disorders, including depression, anxiety, OCD, bipolar disorder, schizophrenia, and dementia. Again, all of these conditions are thought to be far more common now than they were even 20 or 30 years ago.

To be clear, each of these conditions arises due to a multitude of factors. But microbiome imbalance appears to be a common thread that connects them all.

“I think we’ve grossly underestimated how much our microbes mediate our health, and how vulnerable and sensitive they are to variations in our lifestyles and environments,” says Miranda Hart, PhD, an ecologist at the University of British Columbia in Canada. “Our environments and how we interact with them dictates what gets into us, and that in turn dictates our health.”

This is where biodiversity — and its rapid disappearance — comes into play.

What is the role of biodiversity in human health?

The term “biodiversity” refers to the plants, animals, fungi, soil microbes, and other living things that populate a given area.

For a 2017 paper in the journal Frontiers in Microbiology, Hart and her coauthors made the case (one that is now supported by an even larger and stronger base of evidence) that the biodiversity of a person’s living environment correlates with the richness and diversity of their microbial exposures, which in turn affects the populations and health of their microbiome.

Put another way, when the places you spend time in lack biodiversity — and that could be said of most urban and suburban settings in the U.S.— they also lack health-supporting microbes. The consequences of this appear to be dysbiosis and illness. “There are so many things that local biodiversity does for an individual’s health that you could write about it for the rest of your life,” Hart says.

The risk to human health

Unfortunately, biodiversity has plummeted worldwide since the start of the last century, and that decline is only gaining momentum due to climate change. “We are really at a global biodiversity crisis, losing not only entire species but also seeing decreases in the number of plants and animals that are important for natural ecosystems,” said a NASA program scientist in the wake of a 2019 report that found an average 20% drop in species abundance across most land-based habitats since the year 1900.

Nowhere is biodiversity loss more acute than in cities, where natural habitats are frequently cut down, paved over, and sequestered in small parks and private gardens. Making matters worse, many urban green spaces are home to a few trees, some mown grass, and not much else.

Now, there are lots of things in cities that make us sick. Also, the types of people who live in urban versus rural places are often not comparable demographically. That makes it difficult for researchers to nail down the precise level of harm caused by urban biodiversity loss.

Still, there’s evidence that people who live in cities are more likely than their rural counterparts to develop diabetes, multiple sclerosis, allergies, and many of the other microbiome-linked diseases and disorders that science has tied to biodiversity loss.

‘If we just focus on plants, everything else will fall into place.’

How to mitigate these risks

Moreover, research has found that the cultivation of urban green spaces — parks, gardens, urban farming plots, green roofs, green road verges, etc. — can promote improvements in public health via increases in biodiversity.

“Ecosystem health is intimately tied to human health,” wrote the authors of a 2023 paper in Nature Urban Sustainability. “There is increasing evidence that biodiverse green spaces — and their soils in particular — can enhance human health by exposing people to diverse beneficial environmental microbiota.”

What you can do about it

The takeaway from all of this work is that even if you don’t care about nature or the planet or climate change — even if you’re operating solely on a self-interested level — you still have a strong incentive to support public and private initiatives to enrich the biodiversity of your area’s green spaces.

There are lots of ways to do this.

Prioritizing the natural regrowth (sometimes called rewilding) of native plant species is one way to encourage local biodiversity. Many cities and towns are allowing plants and flowers to grow wild by the sides of roads and in designated sections of parks, but they need public backing (and sometimes volunteers) to implement these kinds of changes.

Even if you only have control over your own yard, Hart says your choices matter.

“Stop using biocides,” she says. “Rip up your lawn and plant native plants. That will allow whatever soil microbes and herbivores and pollinators that were adapted to your area to come back.” If you’re not willing to lose your lawn entirely, devoting a portion of it to native plant species will still increase its biodiversity and health. “When you’re working with what is supposed to be there, you won’t have to do as much to cultivate it,” she says. “It’s less intensive and there’s less input required.”

Addressing the problem of biodiversity loss will require a lot more from all of us. Agricultural practices (and subsidies) that push pesticide-treated “monoculture” farming is a major problem, Hart says. So too are all the major drivers of climate change. But if we all support local efforts to enhance biodiversity, it will make a difference.

“I feel like we’re in a really terrible spot,” she says. “We’ve created this situation where we have all these diseases that are directly linked to how we’ve treated the environment.”

“The solution,” she says, “is to plant plants. If we just focus on plants, everything else will fall into place.”