I've had a go at including these once before and then got out of the habit. The idea behind including this theme - and the Goddess month theme - on the blog is to take advantage of the energies they provide. Each month has a particular theme to it and throughout that month we can utilise the energies for ourselves.
The current Celtic tree month is Birch/Beth. It runs from December 24th to January 20th. This is a time of rebirth - in keeping with the winter solstice, which is the time of rebirth - it is a time for looking forward, to the growing light. Traditionally we work for creativity and fertility now. Also healing and protection. It is said that magick performed during this month is quite potent so now would be a good time to spell for positive changes in your life, or for spellwork aimed at shifting problems and so on.
I've heard it said that these beneficial energies are only present around the time of the tree month's full moon, but I don't believe that. I would imagine that the energies are more potent at this particular time - as with any kind of energies - but the month as a whole will have the specific energies stated.