When Winter Loses Its Blanket: How Warmer Seasons Are Breaking an Ancient Partnership Underground

When you walk through a woodland in February, everything looks asleep. The trees are bare. The ground is cold. The birds are quiet. It is tempting to think that nothing is happening.

But beneath your feet, in the dark spaces between soil particles, an ancient partnership is hard at work. Threadlike fungi are growing through the earth and into tree roots, trading nutrients for carbon in a relationship that has existed for four hundred million years.

This hidden world is what makes woodlands work. It is also, new research suggests, one of the first places climate change is breaking things.

The Winter Blanket

In cold places, a thick layer of snow acts like a blanket over the soil. Even when air temperatures drop well below freezing, the ground beneath the snow stays warm enough for life to continue. Microorganisms, including the beneficial fungi that partner with trees, keep working through the winter. They decompose dead leaves and fallen branches. They liberate nutrients. They prepare the soil for spring.

When the snow melts and trees wake up, everything is ready. Roots grow. Fungi grow. The ancient exchange resumes.

But this system depends on timing. The fungi must be active when the plants are active. Their growth needs to overlap.

New research published in February 2026 shows that warming winters are breaking that overlap.

A Thirty-Year Experiment

In the Rocky Mountains of Colorado, scientists have been running an unusual experiment for three decades. They suspended heaters over plots of subalpine meadow and warmed them by two degrees Celsius — roughly the amount of warming that climate models predict for many regions by the end of this century.

Above ground, the results were dramatic. Over thirty years, the grassland plots shifted to shrubland. The lush meadow became more like desert.

Below ground, the changes were just as significant but harder to see. The warmed plots contained noticeably fewer beneficial fungi. The plants growing there were less able to acquire nutrients. They were less resilient to stress.

The researchers, led by ecologist Stephanie Kivlin, also tested what happens when snow melts early. They advanced the snowmelt in several plots by about two weeks. The mycorrhizal fungi responded by becoming active a full week earlier than normal.

But the plants did not.

A Timing Mismatch

This is the problem. Fungi and plants use different cues to know when to grow.

Fungi respond to temperature and to the availability of nutrients in the soil. When the soil warms up and nutrients become available, they get to work.

Plants respond to light as well as temperature. Day length tells them when spring has truly arrived. In a warming world, the soil may warm up weeks before the days get long enough to trigger plant growth.

The result is a timing mismatch. The fungi wake up and start gathering nutrients. The plants stay dormant. By the time the plants are ready to receive those nutrients, much of the nitrogen and phosphorus has already leached away. It washes into streams and lakes instead of feeding new growth.

The researchers call this “phenological asynchrony.” It is a technical term for something quite simple: the partners in an ancient relationship are falling out of sync.

Why This Matters for Woodlands

The research was conducted in mountain grasslands, not ancient woodlands. But the same principles apply anywhere that plants depend on mycorrhizal fungi — including almost all British trees.

Ancient woodlands like those we work with at EcoSentience have built their fungal networks over centuries. The soil contains miles of fungal filaments connecting tree to tree. These networks help trees share nutrients, warn each other of threats, and survive stressful conditions.

If warming winters disrupt this timing year after year, the networks weaken. Trees become less resilient. Nutrients leach away. The soil degrades.

Over time, a healthy woodland can become something else entirely. The Colorado experiment showed grassland turning to shrubland. In a British context, we might see ancient woodlands become less diverse, less resilient, less able to support the birds, insects, and mammals that depend on them.

The Carbon Connection

There is another reason this matters. Mycorrhizal fungi are one of the planet’s major carbon stores.

Plants absorb carbon dioxide from the atmosphere through photosynthesis. They trade some of that carbon to fungi in exchange for nutrients. The fungi use it to build their networks underground. A study led by evolutionary biologist Toby Kiers found that mycorrhizal networks store carbon equivalent to more than a third of global fossil fuel emissions each year.

That makes fungi both a victim of climate change and a potential solution. If fungal networks remain healthy, they lock away carbon. If they degrade, that storage capacity is lost.

Reasons for Hope

The research on warming winters is worrying. But there is also good news: we know how to help.

Conservationists and foresters are experimenting with ways to restore fungal networks to degraded land. One method is deceptively simple: take a small amount of soil from a healthy ancient woodland, and plant it alongside new trees.

In the United States, researchers have used this technique to boost the survival and growth of urban trees. A company in the UK called Rhizocore Technologies has treated more than six hundred thousand trees with fungal pellets and reports a twenty per cent increase in survival and growth rates.

Forestry England has begun moving intact cores of fungus-rich soil from ancient woodlands to newly planted sites. They call it fungal translocation. It works because the fungi are already adapted to local conditions. They know how to partner with local trees.

This is not a substitute for protecting ancient woodlands in the first place. Some fungal networks have taken centuries to develop. Once they are gone, they cannot be fully replaced. But restoration can help damaged ecosystems recover.

What We Are Doing

At EcoSentience, we are working to understand and protect the fungal networks in our own ancient woodland at Mickley Wood in Northumberland.

We are planning an environmental DNA study to map the fungal diversity in our soil. We do not yet know what species are there, or how healthy the networks are. That information will help us understand what we need to protect.

We are also developing environmental monitoring to track soil conditions through the year. Soil temperature and moisture data could help us detect whether our fungi are becoming active earlier than our trees. We may see the warning signs before we see the damage.

And we are exploring acoustic monitoring using BirdNET-Pi, which can track bird diversity in the woodland. Birds depend on healthy insect populations, which depend on healthy soil. If something is going wrong underground, it will eventually show up above ground.

The Hidden World Matters

The fungi beneath our feet do not get much attention. They are invisible. They are quiet. They work in the dark.

But they are essential. They feed the trees that give us oxygen. They store carbon that would otherwise warm the planet. They hold the soil together. They make woodlands resilient.

New research shows that climate change is threatening this hidden world. Warmer winters are breaking the timing that keeps the partnership working.

We cannot see it happening. But we can choose to pay attention. We can study it. We can protect it. We can restore it.

The next time you walk through a winter woodland and everything looks asleep, remember that beneath your feet, an ancient relationship is quietly holding the whole ecosystem together. That relationship is worth protecting.

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This article is based on research published in February 2026 by scientists at the University of Tennessee, University of Michigan, and Rocky Mountain Biological Laboratory. The full paper appears in the Proceedings of the National Academy of Sciences. Additional sources include the Society for the Protection of Underground Networks (SPUN) and the Bulletin of the Atomic Scientists.

If you would like to support our work monitoring and restoring ancient woodlands, please get in touch or donate.