Nature has a habit of finding places to call home even in harsh environments. Some creatures thrive in deserts, our shingle beach garden is battered by storms but some plants and invertebrates cling on. There are even life forms that colonise the edges of ocean floor vents spewing super-heated liquid into the sea. Less extreme but still a difficult place, take a look and you will see there is plenty of life on the walls around town.
When new ground is created by a volcanic eruption there is no soil to hold water or nutrients to support life. After many years, the new land is colonised and a succession of species will eventually incorporate the area as a normal part of the landscape. The first living things to move in will be lichens and mosses. Then larger plants will get a hold and, all the while, animal species will be moving in.
Lichens are fungi with algal plant cells trapped inside. The fungal hyphae spread across the stone or brick surface and capture water and tiny traces of nutrients from rain. Some lichens can actually hold on by growing down into the tiny spaces on the surface of the wall. The algal cells are protected and get on with the job of photosynthesising to produce sugars that feed the fungus.
If you take a look at the brick walls around town, if they have been there for a few years you will see circular patches, mainly white but also green, grey and black. These are lichen crusts, living communities. The white blotches look as if someone has dropped a small ice-cream or perhaps a gull has been passing.
If the wall is wet for long enough, the next incomers will be mosses and liverworts. These relatively simple plants attach themselves with tiny hairs called rhizoids which grow into the minute cracks and imperfections on the wall surface. Once established some mosses produce a mild acid that eats into the stone for better grip.
Once moss has become established it traps grit particles and, mixed with dead parts of the moss, a soil begins to build up. This then allows more advanced plants such as ferns to move in and you start to get seedlings of wild flowers.
As lichens and mosses start to colonise a new wall, that creates a habitat for animal life. If you get a low power microscope on the lichen crust you will see tiny brown blobs less than half a millimetre across walking about, these are mites that feed on lichen. The next incomers will be tiny insects such as springtails. Once these tiniest creatures are there other larger creatures will move in to feed on them.
Given long enough the wall will be taken over by nature. If someone comes back to your new wall in a thousand years they will probably need to be an archaeologist digging to unearth the structure.
Ed Dolphin
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