Cardiff Bay Barrage is a monument to concrete, 135,000 square metres of concrete – in fact, it received an award from The Concrete Society soon after it was completed. And lichens love having so much concrete to colonise!

According to that same Concrete Society, ‘As the concrete ages, the surface alkalinity is reduced by carbonation and the action of rainfall, thus providing a more suitable environment for biological growth.’ And, as lichens are sensitive to air pollution, the almost constant blasting of fresh air aids their lush growth, as you can see from these photos, taken during one of last week’s exercise walks.