Dispatches from the edge of the Empire

Hadrians_Wall_from_Steel_Ri

Hadrian’s Wall from close to Steel Rigg car park, April 2014.

My wife and mother are on holiday together in Jordan and sent me a progress report from the ruined Roman city of Jerash, complaining about the weather (31 degrees Celsius). In a spontaneous show of empathy with their plight in the south eastern corner of the Roman Empire, I decided to visit the north-western border to make my own observations about the weather (11 degrees, strong westerly winds and occasional squally showers).

Having written about Trentepohlia in the previous post, I was alert to any conspicuous orange patches as I walked along the central part of Hadrian’s Wall yesterday. The location for the pictures below is the famous Sycamore Gap (NY 761 677), which was used as a location in the film Robin Hood: Prince of Thieves, apparently. It was easy to spot the distinctive patches of Trentepohlia, even from 100 metres away. What was particularly intriguing was that I only saw it on the north-facing side of the wall. Fabio Rindi and Mike Guiry found no correlation with compass direction in their study (referenced in previous post), though Table 1 of their paper does seem to suggest a slight preference for north-facing walls in Galway. Presumably the north side of the wall receives less direct sunlight, so provides a slightly less harsh environment for the alga. My observations are, also, a rather dramatic validation of their comment about a preference for “old walls” – this section of Hadrian’s Wall having stood here for about 1900 years.

Sycamore_Gap_140412

Sycamore Gap on Hadrian’s Wall (NY 761 677), with patches of Trentepohlia visible on the north side.

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