Shoe tree

Usually shoe trees come in pairs, but it seems from a quick bit of research that there is an entirely other type of shoe tree... This one, rather sparsely populated at the moment, is on Willesden High Road, northwest London.

In July 2010 the US had 76 shoe trees (it says so here); "A shoe tree is usually started off by one person with an enthusiasm for shoe-flinging, a popular sub-cultural activity among American youth. The lone pair of shoes will sometimes attract other shoe-flingers, and within weeks or even days, the shoe tree will be in full bloom."

In January 2009 there was one on the A40 between Stockenchurch and High Wycombe; perhaps it's still there. How, or rather why, it got that way remains a mystery. Who threw the first shoe?