Is Bioenergy Green?

I've long had an uneasy feeling about the efficacy of bioenergy without ever settling down to do the appropriate calculations. Recently I've become aware that accounting methods used in assessing the benefit of bioenergy actually ignore CO2 emissions associated with its production. I gather this was agreed so that there was no risk of double counting but the net result is that C savings from bioenergy are very much less than claimed and in some case may even be negative.

Let's take a simplistic example: I chop down an old tree that's been in my garden for absolute ages and burn it in my living room grate, so displacing the use of a certain amount of coal. I immediately plant a new sapling to replace the old tree. So I've "saved " the CO2 that would have been produced from the coal. However, wood is a poor fuel compared with coal so I've actually produced more CO2 from generating the same heat from my poor defunct tree. Furthermore I've removed the capacity of that tree to absorb CO2 and my new sapling will take up significantly less. Oh dear, I've actually increase global warming by being "green" and using a biofuel.

As I said, this is a simplistic example but with over 60% of the EU's renewable energy coming from biomass there would appear to be the potential for a big accounting problem.