Britain’s fight against climate breakdown may usually look like windfarms or solar energy. But on miles of Lancashire coast the frontline is rather more festive.

Tens of thousands of discarded Christmas trees have been partially buried on beaches south of Blackpool as a frontier against rising sea levels.

In a biting February wind, hundreds of volunteers haul the tinsel-free trees into shallow trenches and let nature do its work. Within weeks, or sometimes days, they morph into sand dunes to protect homes on the seafront.

It might sound like a peculiar festive tradition but conservationists say their work is increasingly vital: since the mid-1800s, the Lancashire coast is believed to have lost 80% of its sand dunes due to the rapid growth of seaside towns such as Blackpool and Lytham St Annes.

“Sand dunes used to extend for miles and miles inland but we’ve colonised and built the towns so now they’re a very thin fragment of what they used to be,” said Amy Pennington of Lancashire Wildlife Trust, which runs the sand dunes project with funding from the Environment Agency.

“They’re important because this is the only form of sea defence that the local community has.”

Volunteers began burying Christmas trees along these beaches more than three decades ago – the Guardian photographer Christopher Thomond first captured the effort in 1994 – but the project has ramped up in the past decade as sea levels have risen.

The UK is estimated to have lost about 30% of its sand dunes since 1900, while sea levels have increased by about 19.5cm. Two-thirds of this rise occurred in the last 30 years, according to a recent study, which is higher than the global average.

Pennington said an increase in storm surges had accelerated the loss of sand dunes, potentially exposing coastal houses to flooding: “We’ve noticed with storm surges, the tide pushes a lot further up the beach so the dunes get washed away more regularly.”

As well as being a natural climate frontier, they are also a vital habitat for wildlife.

Burrowed among the vast Christmas tree dunes in Lytham St Annes are one of the UK’s rarest reptiles.

Hundreds of sand lizards were released into the sandy mounds in 2020, having not been seen in the area for about 60 years, and conservationists say they are beginning to thrive.

“Each year we’ve spotted more and we’ve seen lots of young which means they’re breeding on the dunes,” said Andy Singleton-Mills, the area conservation manager for Fylde council.

Day trippers hoping to spot one of the stripy green and brown reptiles may be disappointed though, he said. They run a mile from humans, meaning tracking them was like “trying to find a needle in a haystack”.

Last week, 650 volunteers got to work on Lytham beach, in sight of Blackpool’s big dipper, burying about 2,000 Christmas trees donated from across Lancashire.

Minus the odd rogue plastic tree and an occasional bauble, they sit along a two-mile stretch of beach decorated with tufts of marran grass, the roots of which can grow as long as 100 metres and help hold them in place.

Pennington said the new dunes, which can grow to about 3 metres (10ft) high, should withstand the elements “hopefully indefinitely”.

But as sea levels rise, she said, they will within the next five years have to start building the dunes upwards, rather than out towards the Irish sea. “Eventually we will get to a point where the tide is regularly meeting the work we’ve done so they will just be swept away. But that doesn’t mean we have to stop building them out, we will just start building them up.”

For some, sand dunes may be an annoying obstacle to getting to the beach. For others, they are place for windswept games of hide and seek.

Holly Moeller, an artist who has painted a watercolour of the Lytham dunes, said people were “in danger of taking them for granted”.

“The sand dunes can look quite sparse and bare but they’re such an amazing habitat – there’s so much going on that you don’t see at first glance,” she said.

“At difficult points in my life when I’ve struggled with mental health, there’s something about the coast and the dunes that is big enough to hold that. It’s a place to come for solace.”