Highcliff Nab: A Crusty Puzzle

Highcliff Nab today, and an enduring puzzle on its crag face. Nearly the entire surface is smothered in light green lichen, except for one striking vertical band where the rock is inexplicably bare, as though the lichens collectively decided this spot was beneath them.

Lichens, those delightful symbiotic oddities born of desperation between fungi and algae, manage to eke out existence in conditions where all sensible organisms give up. They bring a splash of colour to otherwise bleak landscapes and thrive where nothing else dares, from the frozen wastes of Antarctica to the dizzying heights of barren peaks. Humanity, ever resourceful, has made use of them for everything from food to poisons to dyes—you couldn’t imagine Harris tweed without them.

As for identifying this lichen on Highcliff Nab, I will not even pretend to try. Google has offered no insight, beyond the thrilling conclusion that it is a crustose lichen, because, well, it is crusty. What interests me far more than a scientific name is why this one band of rock has been shunned for decades.

Lichens are fussy organisms, sensitive to light, moisture, pH, minerals, and air quality, each species insisting on just that right combination. They are so particular that scientists use them to measure air pollution. Yet this barren patch defies easy explanation. A slight overhang offers some shade, but it is not a cave. It does not seem especially damp or dry, nor is it a popular route for climbers dragging their chalk-covered hands.

Meanwhile, the rest of the crag reminds us of just how tediously slow crustose lichens are to grow. Even the age-old graffiti on Highcliff is slowly vanishing beneath its relentless advance. This lazy growth rate has been put to use by specialists in the sleep-inducing field of ‘lichenometry.’ By measuring how far these crusty little pioneers have spread, they can estimate timescales for everything from glacier retreats to Easter Island statues to earthquakes. All of which is fascinating, but it still does not explain this lichen-free zone on Highcliff Nab.