My last upload, of a crow on a neighbouring roof, showed some lichens. Delia said "I was always told that lichen only grew where there was clean air!! London must have improved somewhat! Or maybe it's only certain types of lichen?"
Here's another shot, minus the crow, and showing well-established lichen growth since the house was built, about 25 years ago.
It seems that indeed it's "certain types" of lichen that can cope with polluted air. In particular, they don't like sulphur dioxide. But from Wiki: "Different kinds of lichens have adapted to survive in some of the most extreme environments on Earth: arctic tundra, hot dry deserts, rocky coasts, and toxic slag heaps. They can even live inside solid rock, growing between the grains... It is estimated that 6% of Earth's land surface is covered by lichens." They may be the oldest living organisms. Some can survive unprotected in space (directly exposed to extreme fluctuations in temperature and cosmic radiation) and, when brought back to Earth, still be able to photosynthesise.
I don't know exactly how dirty London air is (pretty bad probably) but I'm in a fairly elevated position, which might have a bit less pollution.
Thank you for your kind comments on my pictures, and good birding!
John
