Warmer winters and invasive species are changing Howth’s ecology

Nicole Dunne kneels beside a clump of scrawny, grey-tinted nettles, stooping slightly into the path where shins could brush past them in a narrow alleyway in Howth.

She sips her coffee, and then pinches the flat of a nettle leaf. She slips two fingers under the leaf, and produces a tiny bunch of green seeds between her fingertips.

Dunne runs a foraging business, Howth Foraging, where she shows people how to pick, nibble and stew plants that sprout between the winding housing estates.

She pops the nettle seeds into her cheek, chewing with her molars to avoid a sting. The juice bursts into her mouth, she says. “It’s sweet.”

But they should be sweeter and greener, she says. “The winter wasn’t as cold, so they came up too early, thinking it was near the end of spring.”

Climate change has meant rising temperatures in Howth – and beyond, of course – which have changed the natural life cycles of plants and creatures who live there, knocking some out of sync with each other. The changes have also favoured some invasive species, over native ones.

A Too-Warm Winter

Dunne has just passed the house on Balglass Road where she grew up, and hiked up the hill into this narrow alleyway, heading towards Dungriffin Villas.

Near where she was eating nettle seeds, she spots a tall spiky pink flower, towering above a growth of round, horseshoe-like leaves. She picks the winter heliotrope and holds it to her nostrils.

“I love the smell of this, it just reminds me … It’s like vanilla, it’s lovely,” Dunne says. It can be made into a calming tea, she says.

She liberally snatches the winter heliotrope. “It’s actually good to take them up and out. Because these aren’t from here, they’ll kind of take over, so they’re blocking out our native plants.”

Further up the path, a steep staircase leads to Dungriffin Villas. Growing in large, grass-like bunches along the steps is the three-cornered leek, which tastes like spring onion.

Dunne lifts up some of the drooping leaves and points out a few of the early shoots of dandelion and wild garlic, two native plants.

As the climate warms, invasive species from the Mediterranean, like the three-cornered leeks, winter heliotropes, and Alexanders plants, introduced centuries ago, are growing above native plants, getting in the way of sunlight, she says.

A warmer climate also means that native plants won’t come up at the right time, and so may not be there for pollinators and insects to feed on, she says.

When Dunne’s mother and grandmother were teaching her to forage, she remembers there were fewer of these non-native plants, she says.

“There would have been some around, but there wouldn’t have been as many of them.” Instead, she remembers wall pennywort, cleavers, or nettles.

Is This Bad?

Overall, if winters are mild, then you get early development of the plants,” says Astrid Wingler, a professor of plant biology at University College Cork.

Wingler and researchers at UCC were funded by the Environmental Protection Agency to look into the impact of climate change on the phenology, or development cycle, in Ireland, as were researchers in UCD.

“We found an advancement in the development of trees in spring,” Wingler says. As for autumn, some plants are yellowing earlier, or staying green later.

The cause of this depends on the plant, says Wingler. “Not all plants respond in the same way.”

“For some plants, the growth itself is just directly temperature dependent,” she says, while other plants receive specific signals to form the leaf.

But they didn’t do any controlled experiments, she says. Until 2013, the EPA funded a National Phenology Network, which did experiments with birch trees in controlled temperature chambers.

“They found that birch trees need cold temperatures in winter, to promote leaf formation in spring,” says Wingler.

A February 2022 study by the Royal Society found that, due to rising temperatures, since the 1980s, plants in the UK have been flowering about a month earlier – compared to when they flowered each year between the 1750s and 1980s.

“The observed trends and extremes in the UK’s first flowering dataset can affect the functioning and productivity of ecosystems and agriculture,” says the study.

It can result in an ecological mismatch, says Wingler. So if plants haven’t flowered by a certain time of year, pollinators may not be able to pollinate.

“Or if the vegetation isn’t there, when the larvae of the insects feed, then they won’t have anything to feed on. And then maybe the birds won’t have any insect larvae to eat,” she says.

A Fingal County Council spokesperson said on Tuesday that the council does not carry out any phenological studies, and is therefore not aware of any changes in flowering times on Howth or elsewhere in the county.

Where’s the Action?

Dunne says the county council should stop cutting back hedgerows and brambles, as plants should be allowed to adapt to the changing climate themselves, without being interfered with.

“I have seen bumblebee nests destroyed during the summer, the most important time, and trees cut back leaving wood pigeon eggs on the ground,” she says.

Fingal County Council has an invasive species control plan in its Howth Special Amenity Area Order, which gives the area secure protection to preserve its natural environment.

The council spokesperson says it removes Alexanders from Red Rock Beach, cuts away tall vegetation from rare plants there, and plans to create a rhododendron-extraction plan, according to its operational plan.

The central government’s Climate Change Sectoral Adaption Plan, which describes actions the government aims to take to reach net zero emissions by 2050, details the impacts of climate change on plant and animal phenologies in Ireland.

“Increasing spring temperature in recent decades has been shown to impact the timing of key life-cycle events (phenology) in a range of plant species, since 2009,” it says.

Climate change is having a major impact on the spread of invasive species, it says.

Wingler, the UCC professor of plant biology, says the plan is well-researched, but it doesn’t include much action. “It just kind of pointed out the problems. What the solutions are is a different question.”

She suggests improving biodiversity, by planting different kinds of plants. “The more diversity you’ve got in your planting, the better chances you’ve got that the insects have got the food source of the plant, because it’s got many different plant species.”

Declan Doogue, vice president of the Dublin Naturalists’ Field Club, says one gripe he has is local councils planting wildflower seed mixtures en masse, he says.

“It lets the local authorities throughout the country look as if they’re doing something significant. But in fact, they’re doing what’s called forging nature’s signature, putting out a pretence of the real thing,” he says. “They’re getting away with it.”

It would be better, he says, to manage the existing environment better. ““To improve natural diversity, leave it alone. Put in place management operations, that might be from cutting the grass or preventing water from being wasted. Those are the things that matter.”

Dunne, looking up, says she often thinks of the pandemic lockdowns, when the roads were clear of cars, and the skies clear of planes.

“The air was so pure and clean,” she says, without vehicles emitting pollution all around.

The whole ecosystem was thriving, she says, shielding her eyes from the bright winter sun with a cold hand. “It was just amazing the amount of insects. I was delighted.”

She can see it dwindling now again, she says. “And there’s just not as many birds as there was this winter, as last winter. Even the blue tits, or the finches as well.”