In a new article for The Conversation Lecturer in Biology Sven Batke reveals what the humble fern can tell us about climate change.
Ferns are at their most diverse and abundant in the world’s tropical rainforests. This warm and humid ecosystem is heaven for these plants, which unfurl their feather-like leaves in the damp and shaded understory. So how did they ever come to colonise British living rooms?
If you have a potted fern at home, your choice of household companion may have something to do with the Victorians. Pteridomania (pterido comes from pteris, the Greek word for fern) seized Britain in the 19th century, as people competed to cultivate ferns at home and in specialised greenhouses.
Only 70 species of fern can be found in the UK wild, but you can buy over 500 species as house or garden plants today. That’s if you fancy the challenge of growing these fussy flora at home, of course. Ferns are notoriously difficult to keep alive. Too much water and the plant’s roots rot. Too little water and the plant starts sucking up air, causing a blockage which kills it.
Their sensitivity to temperature and rain make ferns ideal indicators for environmental conditions. For example, if your fern’s tips go brown then it probably means the air in your house is too dry.
This property also makes ferns very useful for scientists trying to understand how ecosystems are coping with climate change. By studying how these ancient plants have responded to environmental changes in the past, botanists hope to open a window into the future of the world’s tropical forests.
Ferns first appeared on our planet around 350 million years ago. These plants, which lack flowers and seeds and reproduce via spores instead, helped shape the earliest forests and served as important food sources for many extinct species, including some dinosaurs.
Scientists who research fossil plants have used fern fossils to reconstruct past climates and to study the effect of natural changes in the Earth’s climate system. Ferns are now being used to predict how modern climate change, driven by people burning fossil fuels, will affect plants and ecosystems worldwide.
But since ferns love to grow in warm and wet places, it’s not always easy to study them. Many tropical ferns grow along steep cliffs or up tall trees. No wonder fern species which evolved in the tropics can struggle to thrive indoors and often need extra love and attention during dry summer months.
Honduras, sandwiched between Guatemala, Nicaragua and El Salvador, is about half the size of the UK but is home to more than three times as many plant species, including more than 700 ferns. The mountainous central American country has a tropical climate and vast forests and is often covered by thick clouds.
Growing high up on mountain ledges, some Honduran fern species are doomed by the higher temperatures and lower rainfall which climate models predict for much of the world’s tropical forests. Plant species across the globe have moved up mountains by between 30 metres and 36 metres in the last ten years alone to escape hotter, drier conditions.
When growing conditions take a turn for the worse, ferns have three options. Either disperse to somewhere cooler and wetter, stay and try to adapt to the changing conditions (possible if the environmental changes aren’t too drastic), or go extinct. For most neglected house-grown ferns, the last option is the most common.
And that’s the route which many ferns growing at high altitudes in tropical forests are likely to take as well. In 2018, researchers in Honduras, the UK and US set out to better understand the globally observed trends in plant distributions. Their project is part of a wider effort to write the first fern flora of Honduras. A flora is a book that describes the plant species growing in a particular area or time period.
What the researchers have discovered so far is worrying. When studying the tallest mountain in Honduras (which has a summit at 2,844 metres), they found that up to 32 of the 160 ferns that grow on the mountain will need to shift above its maximum elevation. In other words, these species will disappear, and this is expected to happen in as little as 25 years, perhaps 70 at most.
Wild ferns in the UK and elsewhere in Europe have already begun shifting their distribution in response to climate change, and we can anticipate more severe changes in the near future. These sensitive plants have already told us a lot about the past. Now, they provide an early warning about the future.