How fast do lichens actually grow?

Some crustose lichens in harsh environments grow less than a millimetre per year, but size alone cannot reveal age. Growth varies by species, site and life stage, and reliable estimates need a locally calibrated growth curve.

How can scientists use lichens to date rocks and old buildings?

It's called lichenometry. Scientists identify a suitable species and compare its size with a locally calibrated growth curve, accounting for colonisation delay. This can help estimate when a rock surface was exposed, but not automatically when a structure was built.

Can I damage old lichens by touching them when I'm hiking?

You don't need to tiptoe around every boulder, but avoid scraping, peeling or collecting lichens. Slow-growing species recover poorly from damage, and wet lichen can also be fragile and slippery.

Under Your Boots

The Lichen Growth Rate: When a Patch the Size of Your Palm Might Be Centuries Old

Lichens on fell-top boulders can grow incredibly slowly, but that crusty grey-green circle cannot be aged from its size alone.

8 August 20267 min read