In the UK, arctic-alpine plants are a key component of upland habitats, laying the groundwork for insects, other plants and larger predators to survive in mountain environments. But new research suggests that these species are under threat; withdrawing uphill and perhaps on the verge of vanishing from our slopes entirely. Sarah Watts, a PhD researcher in plant ecology and conservation at the University of Stirling, explains why these plants are so important and why they’re currently in retreat.

^{From Left to Right: Purple saxifrage, snow pearlwort and drooping saxifrage - Sarah Watts}

When most people consider the arctic, or high-altitude mountain landscapes, they think of endless snow, ice and bare rock. But pastel-coloured flowers, sometimes just a few millimetres wide, bloom in these dramatic places too. These miniature flowers not only weather some of the toughest habitats on Earth, but can also help to engineer the landscape for other species.

Don’t be fooled by their delicate petals. Some species of rock jasmine and sandwort grow at well over 6,000 metres on Mount Everest, while purple saxifrage flourishes on the northernmost point of land in the world – Kaffeklubben Island, north of Greenland.

Plants in freezing cold environments are typically small and often form as ground-hugging rosettes, or dense tufts with short stems, known as “cushions”. Antarctic pearlwort sits no more than 5cm high and displays a tight bunch of minute yellow blooms. The summits of the Scottish Highlands, where temperatures can drop to -27℃ in winter, are home to tiny flowers also found in the Arctic, such as moss campion, dwarf willow, trailing azalea and starry saxifrage.

Although plants such as these may appear fragile, their minute size helps them cope with freezing weather and fierce winds. Low stature and tightly packed leaves act as an aerodynamic trap and storage system for water and solar radiation. Microspaces within the dense, dome-like foliage are efficient structures for retaining moisture and heat. An arctic-alpine cushion’s internal temperature can be 15°C warmer than its surroundings.

Cushion plants and mosses can be integral to their local environment. They are known as “keystone species” and “ecosystem engineers” because they stabilise their harsh microclimate, and are often the first to colonise bare ground. As the cushions grow, they improve the moisture and nutrient content of thin soils by accumulating organic material both directly within the plant itself, and through their root systems. By buffering temperature extremes, cushions reduce the frost risk in their immediate surroundings. These processes create a habitat more suitable for less stress-tolerant plant species including arctic-alpines in the daisy and pea families.

Cushion formers are therefore vital “nurse” plants in mountain and polar regions. They also shelter small arthropods including beetles and tiny wingless insects called springtails. These animals may in turn pollinate the plants they take refuge in, and provide food for others higher up the food chain.

^{A rove beetle on snow pearlwort - Sarah Watts}

However, these tiny arctic-alpine plants are now sounding a warning bell for the loss of biodiversity due to climate change. The plants have an important relationship with snow, which offers them protection from disturbance and erosion. But rising temperatures are causing earlier snow melt, allowing the spread of other species previously restricted to lower altitudes and latitudes. Consequently, taller generalist plants, such as common grasses and sedges are crowding out the smaller arctic-alpines.

High mountain areas are warming at twice the global average and are geographically isolated from other places with similar climates, leaving the specialist flowers nowhere to relocate to.

Arctic-alpine plant numbers are plummeting in Britain and climate change is impacting numbers across the world, threatening the future of species that depend on them. Snow pearlwort, a cushion plant usually no bigger than a penny, is the first flowering plant in Britain to have its International Union for the Conservation of Nature status moved from vulnerable to endangered due to climate change. Our research analysing long-term monitoring data from the Ben Lawers National Nature Reserve in the Scottish Highlands has revealed that the British population of snow pearlwort declined by 66% between 1996 and 2019. These data, collected for over 40 years by National Trust for Scotland staff and volunteers, also show that two other arctic-alpine plants have lost over half of their population since the 1990s. As temperatures have risen, snow pearlwort, mountain sandwort and drooping saxifrage have all withdrawn uphill. What’s more, these species face mountaintop extinction here in the UK because there is no higher ground left for them to retreat to.

^{Snow pearlwort growing on Scottish munro Ben Lawers - Sarah Watts}

If we lose these plants from their British mountaintop outposts – at the edge of where they occur globally – this will signal that their strongholds in the Arctic and the Alps are also in danger.

Polar and mountain regions are havens for biodiversity, nurturing species found nowhere else in the world. We risk losing the cultural and inspirational value that rare species give us, with implications for the preservation of our natural heritage.

Plants are the building blocks of habitats and food webs on which other lifeforms across the planet depend, but they are frequently overlooked in conservation news stories. There’s a name for this phenomenon – “plant blindness”. Scientists, nature writers and the media usually turn to trees or species with large colourful flowers to open people’s eyes to the importance of plant life. But we must celebrate and protect our tiniest of plants too. If we don’t, the spectrum of diversity across the Earth’s extremes will be lost for generations to come.

-  Sarah Watts (PhD researcher at the University of Stirling)

A version of this article originally appeared on The Conversation. Changes have been made with the permission of the author.

You can read Sarah’s research via Science Direct and follow her on Twitter.