News: How heat hits wildlife
HOW WELL DID WILDLIFE WEATHER OUR SUMMER? The heatwave, while extreme, has not been the only scorcher in recent years. While we cooled off with a choc ice, our temperate maritime habitats suffered. If this is the future, how will our flora and fauna cope
The UK’s long, dry summer has been welcomed by some – but it has had a serious impact on nature
This is the year the UK sweltered. The satellite heat-map was a rash of red. For six weeks many of us were sleeping badly and praying for rain – and wild things were also feeling the heat.
Sustained warm, dry weather tests the resilience of ecosystems like few other natural phenomena. Climate change will only make scorching summers such as 2018, 2003, or most famously 1976, more common. How will plants, mammals, birds and invertebrates cope and what might the future hold as the global temperature mean creeps upwards?
Some challenges are obvious. Hard-baked soil is impenetrable to the bills of insectivorous birds – not just the blackbirds on our lawns, but also breeding waders such as curlews (already in steep decline).
As earthworms and other soil animals burrow further down in search of cool moisture, mammals are also liable to suffer. Fox cubs and hedgehogs are denied an invaluable protein source; walkers might find starved moles, forced above ground in search of alternative food sources.
Conservationists are keeping a close eye on food-chains: if one link gives way due to dry conditions, the repercussions for other species can be serious. “Seed-eaters that rely on the autumn seed crop might be affected, as many seed-bearing plants are burned off in drought conditions,” says Paul Stancliffe of the British Trust for Ornithology (BTO). “Fruit crops may ripen early and be smaller – that could mean a berry shortage for thrushes and migrant warblers such as blackcaps.”
Winners and losers
As with many insects, butterflies were very visible this summer. “UK butterflies tend to do very well in hot weather,” explains Richard Fox of Butterfly Conservation. “It enables them to be active, find mates, disperse to new areas and, most importantly, lay eggs for the next generation.” But food plants wither in the heat. “Drought impacts severely on the survival of caterpillars of the current generation,” continues Fox. “This leads to depleted populations in future. After the 1976 drought numbers of butterflies didn’t recover fully until 1984.” There are likely to be winners and losers – though it’s a delicate balance. “Some are more drought-sensitive than others. Species such as the speckled
wood and ringlet suffered large declines in 1996 after the very dry summer in 1995. But warm weather may speed the northward spread of butterflies such as holly blue – assuming they aren’t hindered by drought impacts.”
Odd year for plants
Trevor Dines of Plantlife paints a grim picture of the UK’s flora. “Grassland that was full of wildflowers this May and June was brown, parched and desiccated by July,” he says. However, it’s impossible to get a meaningful idea of the current condition of our plant life without considering the longer-term context. As we sweltered, it was easy to forget that this year’s blistering summer followed a long and severe winter.
“It’s turning out to be an extreme – and odd – year for plants,” Trevor says. “The long, hard winter was great as it helped a process called ‘vernalisation’, which stimulates the production of flowers. Though spring was long and cold, many plants flowered like mad through March, April and May. Even up until mid-June, meadows and grasslands were looking fantastic.”
But with little significant rain between May and mid-August, many plants were forced to adopt drastic survival tactics. They jettisoned flowers, leaves and even above-ground shoots in order to withdraw resources into the roots.
In some ways there’s nothing surprising about a heatwave. It’s summer – isn’t it supposed to be hot? “I tend to think this year has been a rare return to what was once normal,” says Jon Dunn, a specialist in orchids. “That’s probably been good for orchids – and indeed other wildlife.” But as the drought dragged on, he adds, laterflowering orchid species found life hard, wilting or even failing to flower.
The immediate impacts of drought can be dramatic, but what’s often more important is resilience – the capacity of a species or ecosystem to return to good health once normal service has been restored.
Jeremy Biggs of the Freshwater Habitats Trust is keen to stress the natural variability of water levels in ponds, lakes and rivers. “Droughts are normal in fresh water,” he says. “About half of everything that lives in water is fine with drought. There’s a range of aquatic plants that are happy with, or even need, periods of drought. The plant starfruit, for example, is fine in temporary ponds.”
Froglife patron Jules Howard is similarly upbeat about the potential of freshwater habitats to handle the heat. “I’m not too concerned,” he says. “It has been a splendid year for pond-watching, because so many animals are drawn towards them for water. Ponds have incredible value in years like this.” Jules goes into detail on life in the ‘drawdown zone’ – the area exposed as a pond’s water level is lowered in the summer.
“One of the myths
“Species of bird that feed on aerial insects had a bumper breeding season, but species that depend on soil invertebrates suffered.” Paul Stancliffe, BTO
about ponds is that they should stay full all year. In fact, in the classic ponds that nature creates, each will regularly have seasons where the water pulls back, opening up this new environment. Most wetland animals are adapted to deal with dry years or dry seasons. Some amphibian tadpoles, for instance, speed up their growth in such years, metamorphosing at a smaller size to get clear of the shrinking waters.”
Problems can arise, though – and the picture can grow more complex – when we factor in variables other than drought alone. Us, for example. Consider peat bog: it’s a pretty tough habitat, when it’s allowed to be. Rob Stoneman, the chief executive of the Yorkshire Wildlife Trust, characterises sphagnum mosses, the keystone species of healthy bogs, as the “ultimate ecosystem engineers”, adapted to wet conditions yet resilient to drought.
“A walk across a peatland landscape in the blistering heat of summer 2018 would have left footprints in white crispy sphagnum moss, dried and seemingly dead as the water-table fell away,” Stoneman says. “However, sphagnum has evolved to cope with drought. It loses water from the top of the moss-mat, yet below, water within the peat is drawn upwards to keep the moss alive. Through this ecosystem engineering, sphagnum mosses
maintain water-tables close or near to the surface throughout the year.”
Things go wrong when we step in. “If we burn a bog to encourage heather at the expense of sphagnum, or cut drains to lower the water-table, the situation changes,” Stoneman says. “The ecosystemengineer properties of sphagnum are lost. Rotationally burnt peatlands of the North York Moors in 1976 never recovered, as the peat was entirely burnt away in places. As this summer’s wildfires in Lancashire showed, the impact can be catastrophic.”
The human impact
Ponds and streams, too, become more vulnerable if human activities skew the system. Jeremy Biggs stresses that a healthy response to extreme temperatures is only possible in a healthy freshwater habitat. Where a water body is polluted, the resilience of its ecosystem is compromised. A heatwave lowers the water level, but the level of pollution remains the same, resulting in a more intensely polluted habitat. “From the perspective of clean standing water, I don’t think droughts are problematic,” Biggs concludes. “Droughts are occasional, but pollution is everywhere.”
How occasional droughts will be in future depends on the global climate – which is getting hotter at a frightening rate. The long, hot summer of 1976 was a British phenomenon in a broadly normal Europe, but this year we were locked into something bigger. Everywhere in the Northern Hemisphere was hotter.
“Climate change has greatly increased the frequency of severe heatwaves over much of the globe,” says Corinne Le Quéré, director of the Tyndall Centre for Climate Change Research at the University of East Anglia. “Studies that have separated the role of human-caused climate change from natural cycles show that the risk of heatwaves has more than doubled due to climate change so far in large parts of the world.”
How will our wildlife respond, if summers like this one become the norm? Change isn’t always destructive for everyone. Droughts and hot weather create new habitats, and insectivorous birds such as swifts, swallows and spotted flycatchers may prosper in a hotter Britain. We might also see further colonisation by Mediterranean birds such as hoopoes.
On the flipside, Britain’s montane habitats will warm, snowlines will creep higher, and we could lose specialist breeding birds such as snow bunting, as well as alpine flora such as saxifrages.
Wild things will often find a way to cope, even as temperature records tumble. But the reality is that in the decades ahead, in Britain and beyond, the flora and fauna of the landscape as we know it will be tested to its limits.
No, it’s not India or Australia. It’s a pond in an English village (in 2006, another challenging year for wildlife). Such sights could become more common in the UK. Inset, right: baked soil made it difficult for insectivores such as blackbirds to find food.
Right: the 2018 wildfires, such as in Lancashire, may cause permanent peatland damage. Far right, from the top: watercourses dried out, but many freshwater habitats could cope; the heat benefitted some of our native butterflies, including the purple emperor.
Peat bogs can balance drought and flood – but only if we leave them alone.
RICHARD SMYTH also wrote this month’s feature on kittiwakes (see p32).