'Dog zone' on trees

[Monkey Orchid]

When I went on a walk at Burnham Beeches a couple of years ago with a chap who knows his lichens, he showed us the area at the base of trees which he referred to as 'the dog zone', i.e. the area low down on tree trunks where dogs pee against the bark. He said that increased nitrogen pollution levels in this area led to the development of algae which prevented the establishment of lichens, so you can see a distinct 'no lichen growth zone'.

I photographed this oak tree at Thatcham Reedbeds. The darker area at the bottom of the trunk looks like an example of 'dog zone'... Is this a concept anyone else has come across?

[Deb London]

Oh my, I love this. I've never noticed this before. I'll be on the look out now.