Restoring nature, saving the city: how 60,000 trees can kickstart a beauty spot’s revival and stop urban flooding

The solution being used is nature’s own engineering - the planting of 60,000 trees.

High up in the Dublin-Wicklow mountains where the Dodder River rises, banks of native hazel, hawthorn, holly, alder, rowan and birch will be planted to create beautiful woodland gullies.

Far down in the city where the Dodder weaves its way through neighbourhoods and business districts, the result will be enjoyed through stable river levels and a much-reduced risk of flooding.

How the idea works was explained by ministers Eamon Ryan and Malcolm Noonan and the team of National Parks and Wildlife Service (NPWS) rangers who are turning it into a reality.

They gathered on International Biodiversity Day in the stunning new addition to the Wicklow Mountains National Park – a 2,000 hectare valley at Glenasmole which is in Co Dublin but forms a natural extension to the 23,000 hectares of national park across the county boundary.

The state bought it several years from NAMA which had taken it over from a developer at the beginning of the downturn in the mid-2000s.

At the time there was a real fear that a private buyer would snap it up and fence it off but now the only thing that will be fenced off are the saplings.

Some will be clustered in enclosures and others individually wrapped in tubes or mesh cages until they are tall and sturdy enough to survive without protection.

Nature could do the job alone if it wasn’t for the large numbers of non-native sitka deer and the sheep that graze the area, stripping it of new growth.

With help, however, this is set to become a flagship example of nature restoration in action.

“With trees, you’ll have small birds and with small birds come the birds of prey,” said Mr Ryan who was the first to spot a lone peregrine falcon hovering over the exposed mountainside. “You get a cascade of action going in the right way.”

You also get a landscape knitted together with an extensive network of roots that makes it far better able to absorb the heavy rainfall that regularly pounds the area.

“When it rains, there is nothing to soak it up so it rushes down, taking the peat with it. All that runs into the Dodder here and on into the reservoir where it has to be removed for the drinking water supply,” Mr Ryan said.

The torrents of water gushing down the mountain also swell the Dodder dangerously in the city where various flood alleviation works have taken place and more are proposed.

“We’ve a choice. Do we do a massive flood protection along the Dodder, where we culvert and pour huge amounts of concrete, or do we do this sort of project, allowing the trees to do the work?” Mr Ryan said.

Local sheep farmer Donie Anderson answered that one, pointing to the narrow stream that is the infant Dodder and the modest clusters of trees hanging on valiantly against the grazers.

“You’d need to be looking at it every day to see this but where there are trees there, they soak up the moisture,” he said.

“One day last week there was a flood in the river and now there’s only a couple of inches of water.”

The restoration project won’t interfere with his grazing rights so he’s happy to see the NPWS rangers out plotting planting spots.

With the EU’s draft Nature Restoration Law and domestic land use reviews proving contentious, projects such as Glenasmole need to be more widely seen and understood, Mr Ryan said.

“It’s not hugely expensive – about €1.5m over three or four years – and the return we get from that is beyond compare.”