What Happens Underground When Winters Get Warmer?

Look across a snow-covered winter landscape and nature seems fast asleep. But beneath the surface, a hidden world is bustling with activity. Tiny organisms are decomposing last year's dead plants and organic matter, creating the nutrients that'll fuel spring growth when the snow melts.

Now, a 30-year study from the Rocky Mountain grasslands reveals what happens when climate change warms these winters: the delicate underground partnerships that sustain life above ground are falling apart.

Researchers found that plots warmed by just 2 degrees Celsius showed dramatically fewer beneficial fungi that help plants access nutrients. Above ground, grasslands transformed into desert-like shrublands. Below ground, an invisible crisis was unfolding.

The Hidden Partnership Economy

Arbuscular mycorrhizal fungi live inside the roots of over 75% of plant species worldwide. These thread-like organisms form web-like networks, supplying up to 50% of a plant's nutrients and water in exchange for carbon that plants produce through photosynthesis. It's a deal that's sustained terrestrial life for hundreds of millions of years.

Winter snow acts like a blanket, insulating these fungi and other microorganisms. Even when air temperatures plunge below freezing, the soil community keeps working, breaking down organic matter and preparing nutrients for spring.

But when rain washes away snow or when snowpack fails to form properly, soil water freezes—and so do the fungi.

When Nature's Clock Gets Confused

The researchers conducted an early snowmelt experiment in April 2023, advancing snowmelt by about two weeks across five large plots. The results revealed a troubling mismatch: fungal growth advanced by one week, but plant root growth didn't change at all.

This timing problem stems from different biological cues. Plants respond to both light and temperature, while underground microorganisms respond primarily to temperature and nutrient availability. When warmer winters activate fungi before their plant partners, the nutrients that fungi extract from soil can't reach the plants that need them.

It's like having a delivery service that starts working before the customers wake up—the goods get processed, but nobody's home to receive them.

The Great Nutrient Leak

Early snowmelt creates another problem: nutrient loss. When microorganisms decompose organic matter in warmer soils, nutrients accumulate in air and water pockets between soil particles. These nutrients should be available for fungi to transfer to plants.

But if rain falls or snow melts before plants become active, these nutrients wash away into lakes and streams. The effect mirrors fertilizer runoff from farms—nutrients fuel algae growth, creating oxygen-depleted dead zones, while plants in the field face nutrient scarcity.

This phenomenon is already documented across ecosystems ranging from Colorado mountain grasslands to New England temperate forests and the Midwest. Without thick snowpack, soils can also freeze for longer periods, reducing microbial activity and leaving fewer resources available when spring arrives.

Ecosystem Transformation

The 30-year warming experiment revealed the scale of these changes. What started as predominantly grassland shifted to more desert-like shrublands. Underground, the decline in beneficial mycorrhizal fungi left plants less able to acquire nutrients or buffer themselves against environmental stresses like freezing temperatures and drought.

These changes ripple through entire food webs. As grasses and wildflowers that cattle and wildlife depend on decline and get replaced by desert-like vegetation, the impacts cascade upward through the ecosystem.

The timing mismatches aren't unique to soil fungi. Mountains of evidence worldwide show how early snowmelt leads to flowers blooming before pollinators arrive, disrupting relationships that species have depended on for millennia.

The Resilience Question

Ecosystems often show remarkable resilience. Organisms might acclimate to lower nutrient concentrations or shift their ranges to more favorable conditions. Some fungi might evolve different temperature responses, while plants might adjust their growth patterns.

But adaptation takes time—often more time than our rapidly changing climate allows. How plants and mycorrhizal fungi adapt together will determine whether these underground partnerships can survive the transition to a warmer world.

The stakes extend far beyond grasslands. These soil communities support global agriculture, carbon storage, and the foundation of terrestrial food webs. When the hidden world below ground gets disrupted, the effects eventually surface in ways we're only beginning to understand.