Tiny universes

Poponessi is a senior researcher at Eurac Research’s Institute for Alpine Environment, where she studies bryophytes – the collective name for mosses, liverworts, and hornworts. Among the oldest land plants on Earth, they colonized the continents around 470 million years ago, long before forests as we know them existed. Unlike flowering plants, bryophytes have no true roots. They anchor themselves with thread-like rhizoids and absorb water and nutrients directly through their surfaces. Their sexual reproduction depends on water, as it needs a primitive, swimming sperm that uses its tail to move through a thin layer of water to reach the egg. Bryophytes are also poikilohydric, meaning they cannot regulate their own water content. Instead, they dry out during drought and rapidly rehydrate when moisture returns. A seemingly lifeless brown cushion can become vividly green within minutes of rainfall. This remarkable adaptation allows them to survive in some of Earth’s harshest environments, while also making them exceptionally sensitive to environmental change – one reason scientists like Poponessi study them.

A patch of moss is far more than a plant – it is an entire ecosystem. Among its tiny stems live tardigrades – sometimes called water bears, nematodes, rotifers, mites, springtails, and countless other microscopic animals. For them, a few square centimeters of moss is the equivalent of a vast forest, providing shelter, moisture, and food. Many have evolved extraordinary survival strategies. Tardigrades can dry out almost completely, curling into a dormant, shriveled state known as a tun until rain returns, while many nematodes survive drought through suspended animation. Together these tiny creatures form complex food webs that recycle nutrients, decompose organic matter, and help maintain healthy soils. Under a microscope, what appears to be a simple patch of moss becomes a bustling world – proof that some of nature's richest ecosystems exist on the smallest of scales.

When not out in the field or forest, Silvia can be found in the lab, using a microscope and botanical keys to identify the fascinating bryophytes that act as indicators of ecosystem health.

Credit: Eurac Research | Annelie Bortolotti

Nature’s environmental sensors

Bryophytes act as natural indicators of ecosystem health. Because they absorb water and nutrients directly from rain, fog and the surrounding air, they also absorb pollutants. Some species accumulate heavy metals and airborne contaminants over many years – a process known as bioaccumulation – allowing scientists to measure pollution levels. Others respond by disappearing altogether. “The absence of certain species can tell us just as much as their presence,” says Poponessi.

Changes in bryophyte communities can reveal declining air quality, shifts in climate, altered forest conditions, or changes in humidity long before these become obvious in larger plants. Although individual bryophytes are highly sensitive to their environment, the communities they form are remarkably stable because most species grow only millimeters each year. That stability makes even subtle changes especially meaningful, making long-term monitoring an invaluable tool for detecting environmental change.  “In many habitats we only need to repeat surveys every five years,” Poponessi explains.

Bartramia pomiformis (Apple Moss) - you can see where the specific epithet comes from...

Credit: Eurac Research | Silvia Poponessi

Monitoring these miniature forests

At Eurac Research, bryophytes are being studied as part of the “Biodiversity Monitoring South Tyrol” (BMS) project, a long-term initiative that involves studying the biodiversity of 320 terrestrial sites, with 64 sites surveyed annually and data collected every 5 years. This project monitors many plant and animal organisms to study the province’s biodiversity and how it changes over time. Among the plant organisms monitored are bryophytes, which belong to the cryptogams – plants and plant-like organisms that reproduce via spores rather than seeds or flowers. Despite their ecological importance, bryophytes are often overlooked in biodiversity surveys, along with lichens and ferns. Monitoring them requires extraordinary patience and precision.

As part of the BMS project, forest sites and human–impacted areas were selected to study epiphytic bryophytes – mosses and liverworts that grow on tree bark. In this dedicated survey, tree trunks are sampled using a circular plot positioned approximately 1.20 meters above the ground. Whenever possible, each tree is surveyed at the four cardinal directions – north, south, east, and west – as differences in sunlight, humidity, and exposure can support distinct bryophyte communities on each side of the trunk. Within each sampling area, all species are identified and their percentage cover is estimated for each cardinal section.

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Looking more closely

Fieldwork often attracts curious passers-by. “People stop to ask what we’re doing,” Poponessi says. “Sometimes they tell us stories about their favourite forests or about hugging trees. They become fascinated when they realize we're studying something they’ve probably walked past thousands of times.”

Bryophytes may be small, but they perform huge ecological roles. They store water, stabilize soil, provide habitat for tiny invertebrates, contribute to nutrient cycling and help scientists understand how environments are changing. They remind us that some of the most important stories in nature are written on the smallest scale.

Exsertotheca crispa

Credit: Eurac Research | Silvia Poponessi