What is biodiversity, and why does it matter?

Biodiversity is not simply a count of species. It operates at three interconnected levels, each essential to the health of the whole. Biodiversity recovery is central to rewilding, which aims to restore the ecological processes that sustain it.

• Genetic diversity, the variation of genes within a species. High genetic diversity gives populations resilience to disease, climate stress, and environmental change. Low genetic diversity is a warning sign: it means a population is one bad season away from collapse. It also matters directly for restoration success, plantings sourced from a single narrow gene pool are far more likely to fail.
• Species diversity, the variety of species in a given area, and their relative abundance. A forest with 40 tree species functions very differently from a monoculture plantation. Each species plays a role, as predator, prey, pollinator, decomposer, or engineer, that other species depend on.
• Ecosystem diversity, the range of habitats, biological communities, and ecological processes across a landscape or region. Forests, wetlands, grasslands, rivers, and coasts each support distinct communities and perform distinct functions. Losing any one degrades the whole.

These three levels are deeply interdependent. Lose a keystone predator and prey species overpopulate, strip vegetation, and collapse the habitat that dozens of other species depend on. Lose a pollinator and the plants it services fail to reproduce, taking with them the insects, birds, and mammals that fed on their fruit and seed. Every loss sends ripples.

Why biodiversity matters

Biodiversity is not an abstract conservation ideal. It delivers concrete, measurable benefits to human wellbeing, economic stability, and ecological function, benefits that economists call ecosystem services.

Clean water and air

Diverse plant communities filter water, stabilize riverbanks, and regulate runoff. Forests and wetlands act as vast natural water treatment systems. Remove the vegetation and water quality collapses; floods and droughts intensify. The loss of tree cover in a single watershed can affect drinking water for millions of people downstream.

Carbon storage and climate regulation

Biodiverse ecosystems store more carbon than degraded ones. Old-growth forests, intact peatlands, seagrass meadows, and kelp forests are among the most carbon-dense habitats on Earth. When biodiversity collapses, so does their capacity to store carbon, turning natural sinks into sources of carbon emissions. Protecting and restoring biodiversity is inseparable from addressing extreme weather.

Food security

Approximately 75% of global food crops depend on animal pollinators (FAO). Wild insects, birds, and bats pollinate everything from almonds to avocados to coffee. The genetic diversity of wild crop relatives provides the raw material for breeding disease-resistant, drought-tolerant varieties. Lose that diversity and modern agriculture becomes acutely fragile.

Medicine and scientific discovery

More than 50% of modern medicines are derived from or inspired by natural compounds (WHO). Penicillin came from mold. Aspirin from willow bark. Cancer treatments from Pacific yew trees. The biodiversity we have not yet studied may contain solutions to diseases we have not yet faced. Every species lost is a library burned.

Resilience to shocks

Biodiverse systems are more stable and more resilient. When one species declines, others can fill its role, a principle ecologists call functional redundancy. Simplified ecosystems are brittle: remove one component and the whole structure is at risk. The more diverse a system is, the better it can absorb disturbance and recover.

"The challenges of biodiversity decline, climate change and human well-being are closely connected, and a failure to jointly address the dual crises of climate change and biodiversity decline can compromise people's good quality of life."

, IPBES Global Assessment Report on Biodiversity and Ecosystem Services, 2019

Measuring biodiversity: citizen science tools

The more people record, the better our picture of biodiversity becomes, and the stronger the scientific case for protecting it. Whether you are in a garden, a park, or a city street, every species you record adds to the picture.

The scale of biodiversity loss is difficult to comprehend. The numbers are stark:

The five primary drivers are habitat destruction, overexploitation, climate change, pollution, and invasive species. All five are accelerating. All five are caused by humans. And all five can be addressed, at least in part, through rewilding.

Rewilding is one of the most powerful tools available for biodiversity recovery. Unlike traditional conservation, which focuses on protecting what remains, rewilding aims to restore ecological processes, reintroducing missing species, reconnecting fragmented habitats, and allowing natural systems to rebuild themselves.

The evidence is compelling. Where wolves have been reintroduced to Yellowstone, biodiversity has increased across multiple trophic levels, from willows and cottonwoods to beavers, songbirds, and fish. Where beavers have returned to rivers across Britain and Europe, wetland habitats have expanded, water quality has improved, and species that had disappeared for decades have returned. Where large herbivores have been reintroduced to degraded grasslands, soil health, plant diversity, and invertebrate abundance have all increased.

Rewilding works because it addresses root causes rather than symptoms. It doesn't just protect individual species, it restores the ecological relationships between them. And ecological relationships are what biodiversity actually is.

Key rewilding approaches for biodiversity recovery

• Apex predator reintroduction, restoring wolves, lynx, and other top predators to regulate prey populations and trigger trophic cascades that rebuild vegetation, rivers, and habitat structure.
• Keystone species reintroduction, returning beavers, wild boar, bison, and other ecosystem engineers whose activities create habitat diversity that hundreds of other species depend on.
• Wildlife corridors, connecting fragmented habitats so species can move, disperse, and maintain genetically diverse populations across landscapes.
• Invasive species management, removing species that outcompete native flora and fauna, restoring the conditions in which native biodiversity can recover.
• Marine rewilding, restoring seagrass meadows, kelp forests, and oyster reefs that underpin oceanic biodiversity and sequester vast quantities of carbon.
• Reducing disturbance, in many landscapes, the most powerful rewilding intervention is simply to stop intensive management and let natural processes re-establish. Biodiversity often recovers faster than expected when given the space to do so.

Biodiversity recovery is not only a policy challenge, it is something that can be advanced at every scale, from continental rewilding projects to a suburban garden:

• Plant native species in your garden and remove invasive ornamentals
• Leave areas of your garden unmown and undisturbed to create invertebrate habitat
• Support organizations working on habitat restoration and species reintroduction
• Advocate for wildlife corridors and nature-friendly land management policies in your region
• Buy certified sustainable food and wood products to reduce habitat destruction in supply chains
• Stay informed, biodiversity loss rarely makes front pages, but it is one of the defining challenges of our century