Tree with a number

This morning I was checking out a possible route to run next week when it's my turn to host the Carnethy Women's night run. I'm thinking about taking the group along the Water of Leith from Colinton towards Currie and turning off at the Blinkbonny Road. It was there that I spotted this numbered tree. I used to see a lot of these small blue labels on trees in the Hermitage, when I lived a few miles further west. I think it means they are recorded by the Council somewhere, but why?

If you're still with me, the route from the Blinkbonny Road could double back through the wood to Woodhall Farm, and then up the hill to Tiphereth. There's a track over the golf course at Torphin which is suitably far enough out of sight of the club house, and provides a very nice short cut to Torduff Reservoir. The last leg would be over to Bonaly and then home. Around 6 miles. Does this sound ok? Anyone want to come?