Toppled, eaten, pooed on, licked, rusted and stolen: life’s tough for the treasures of Yorkshire Sculpture Park

Its works by Moore, Hepworth and Gormley are priceless. But they are at risk – from toxic bird poo, shifting tree roots and 400,000 greasy humans. We spend a day with the team keeping everything safe

On a blustery hillside near the summit of Yorkshire Sculpture Park, Clare Lilley and I are communing with the landscape. Lilley, YSP’s director and chief curator, has beckoned me through a gate into a piece by the British sculptor Andy Goldsworthy, a drystone wall encircling the trunk of a large lime tree. Inside the enclosure, beneath the tree’s canopy, all we can hear is the shushing of the leaves and the crackle of the wind in the grass. It is cool and tranquil. Then Lilley spots something across the field: a herd of cows is menacing her four-wheel drive. “They like to lick the windows,” she says, then looks at me with genuine concern. “You’re not frightened of cows, are you? We can shoo them out of the way.”

Herding lessons are not on the curriculum at most art schools, but YSP is hardly your average gallery. The largest sculpture park of its kind in Europe, draped across 500 acres of rolling fields, moorland and woods in the hills above Wakefield, it displays more than 100 large-scale pieces and installations, nearly all modern and contemporary. Some of the works are nestled safely inside modest indoor galleries, but most sit in the open air, exposed to everything the Yorkshire climate can throw at them.

As Lilley and I jounce around, it all seems utterly, well, natural. A grouping of angular, humanoid Barbara Hepworth bronzes cluster on a hillside, looking as if they have stood there since prehistoric times (they date from 1970). Walk past the Goldsworthy drystone enclosure, erected last year and intended to resemble a sheep fold, and you might not even realise that it is art.

Such connectedness with the landscape is, of course, a necessary illusion. Keeping millions of pounds of sculpture safe and in pristine condition, and making the park visitable and accessible to 400,000 visitors a year, is a mammoth task. “It’s not something you can study for, honestly,” says Lilley, as we pile back into the cow-licked car. “We’re learning the whole time. It’s fun!”

As we head off in search of an Antony Gormley, Lilley and her technical manager, Simon Skirrow, talk me through some of the challenges the team face every day. Simply getting pieces installed is often a headache, given the size and weight of large bronzes or stone sculptures, and the terrain; for all the riches of its permanent collection, one of YSP’s most prized possessions is an all-terrain forklift truck. Most sculptures are set in huge concrete bases, which are dug into the ground then turfed over. As well as deterring thieves, such as those who stole a large Henry Moore bronze from the gardens of the artist’s foundation in 2005 and melted it down for scrap, this ensures they don’t shift or catch the wind (gales are hardly unknown in these parts).

“We have a lot of conversations with structural engineers,” says Skirrow. “And crane work, being skilled in lifting, understanding where the centre of gravity is in a huge chunk of marble – that’s a real art.”

Another obvious factor is the weather. Even pieces on temporary display are outside for nine months or more, enduring temperatures that range from well below freezing to last year’s record summer heat, plus rain, sleet, snow, hail, damp fog and everything else. Bronze oxidises because of its copper content, but is hardy – “You have to do a lot of damage to a bronze to write it off,” says Lilley cheerfully – particularly if it is coated in protective wax, which should ideally be replaced annually. But painted steel chips and flakes, and stone is porous, meaning that it can freeze then crack.

Daylight itself poses a problem: whereas illumination levels are obsessively controlled in most indoor galleries, here art is at the mercy of the elements. “UV light is incredibly destructive,” says Lowri Moris, one of YSP’s regular conservators, when we speak a few days later. “Especially to paint. Obviously it fades the colour, but the chemicals alter, so the paint breaks down. And then you risk rust.” If an artist is still alive, they can be consulted on repairs, but for historic pieces conservators are often reliant on estates to document how they were made and what finishes and colours were originally used.

Ideally, of course, things should not get damaged at all, the reason why museums and galleries have rigorous inspection routines for objects in their care. At YSP, every work is “condition-checked” daily, to monitor changes, and cleaned regularly. “You want to keep on top of it in a place like this,” says Skirrow balefully.

Imagination is often required. The only way to keep Roger Hiorns’ 2008 installation Seizure – the interior of a real-life former council flat whose surfaces are covered with a dense coating of peacock-blue copper sulphate crystals – immaculate is to clean it meticulously with toothbrushes. “Visitors bring mud and dust and hair, dead skin,” says Moris. “You wouldn’t believe the accumulation of human matter.”

Some pieces are designed not to be touched. Another work Lilley escorts me to, a purpose-built installation by Heather Peak and Ivan Morison, is a low-slung circular wooden pavilion set in a stand of birch trees next to a lake. Over time, it will decay and decompose, eventually disappearing almost without trace. Nature will, gradually and beautifully, defeat human intervention.

YSP is, obviously enough, a park, and the sheer variety of landscapes – dense woodland, lakes and rivers, fields of wild grass, manicured gardens – are a major part of the attraction. But plant life is voracious. Nettles and other weeds, brambles, grass and ivy will swallow anything left untended for long. Algae and moss cling to stone. Tree roots shift beneath sculptures, destabilising them. The effects of the climate crisis are already being felt, Lilley reveals: storm damage from torrential rainfall caused issues last winter, while last summer they were on alert for wildfires.

The Gormley sculpture, when we locate it in a clearing deep in the forest, is another fascinating example of how you install art in dialogue with its environment. A slender human figure fabricated from cast iron, flecked with tawny rust, it is installed high in the air on the sawn-off stump of a dead tree. Or, as it turns out, a number of trees. “The last time, wasps ate the tree from the inside,” says Lilley. “We had to work with Antony to choose a new site.”

Oh yes, wildlife: there’s plenty of that, too. Henry Moore requested that his sculptures be installed in fields where livestock grazes, “which is great, but then you have the sheep problem,” says Moris. What problem exactly? “There’s lanolin in their fleeces, and if they rub up against sculptures, it can change the colour of the bronze.” Bats have also caused issues, as when a nest was discovered nestling inside a piece by Ai Weiwei. “The bat guy was pretty cool about it,” says Lilley.

Bird poo is even more toxic – high acid content – and birds, notes Moris, seem to relish sitting in trees that overhang priceless pieces of art. “You have to clean it off as quickly as you can,” she sighs. “It’s part of the maintenance plan.”

Not that everything can be planned for. As Lilley and I drive out of the wood towards a far-flung corner of the park, we pass a throng of 11-year-olds, here on a school trip, moving at speed towards some Damien Hirsts. Lilley waves to them gaily, but Moris is more upfront about the dangers. YSP stations invigilators at high-risk points, but plenty of the sculptures are unattended.

“Actually, it’s not just kids,” Moris says. “People love touching, although we try to encourage them not to. And when you have 100,000 people a year touching something, it has an impact.” Sunscreen on people’s fingers makes things worse, she adds. “It’s really greasy, so it’s hard to remove from any porous surface. I’m always amazed we put it on our skin, actually.”

Some folk can’t resist climbing on top of sculptures, even though they are enjoined not to. “Walking boots have a lot of metal fittings, people wear jeans, with metal studs. It’s so easy for things to get scratched,” says Moris. Is there any vandalism? “Mercifully little,” says Lilley. “People tend to respect the work.”

In a way, this is the point. Everyone I speak to at YSP is insistent that it is essential to allow visitors more freedom than they might experience in a traditional museum or gallery environment. The relationship with sculpture is more intimate, less reverential. Letting kids run wild around Elisabeth Frinks or a hikers squeeze around Robert Indiana’s LOVE for a selfie is part of the pleasure of experiencing art in a context like this. And the work itself is in dialogue with the ever-shifting environment – subtle changes in light and temperature, the relentless progress of the sun, the rugged poetry of weather and wildlife.

By now, Lilley and I are on another hill. She tells me about coming to this spot in the spring, underneath glowering late-winter clouds, and seeing one of their most renowned Moore sculptures, Three Piece Reclining Figure No 1, silhouetted starkly against the skyline. “I’ve been here for so long, but I’d never seen it look like that before,” she says quietly. “It looked like a different sculpture. I almost didn’t recognise it. How amazing is that?”

Yorkshire Sculpture Park, West Bretton.