Right, you’d need to be positive that biomass is replacing what’s burned in order to call it neutral. On some drawn out time scales this is practically guaranteed, but in the short term it’s very easy to burn far too much without ensuring replacement occurs at a scale and speed that is sustainable.

I suppose you could use byproducts of selective logging where replanting is occurring and actively managed and maintained. Where I’m living there are forests that are quite well managed for lumber such that what’s removed will likely be replaced by the time logging occurs again. Using a similar practice for biomass plants could conceivably be called carbon neutral.

I have a feeling it wouldn’t generate nearly enough biomass conveniently or efficiently enough. I don’t know though. It must take incredible amounts of mass to generate useful amounts of energy.