If a tree falls in the forest—and is then burned to produce electricity—is it carbon neutral? That’s the updated koan that Massachusetts is meditating on as it considers new regulations on the use of biomass as a renewable energy source.

Like many states, Massachusetts has a set of renewable portfolio standards that requires electricity suppliers to get an increasing percentage of their energy from renewable sources. Earlier this year, the state’s Department of Energy Resources came out with a proposed set of rules that would regulate the efficiency of biomass plants and the sorts of material they’re allowed to use if they want to be deemed renewable.

Among other things, plants would have to operate at 60 percent efficiency to qualify for a full renewable energy certificate and at 50 percent efficiency to get a half certificate. The biomass industry finds that prohibitively restrictive. Rob Cleaves, president of the Biomass Power Association, told AOL Energy that no pure biomass-to-electricity plant can meet the standard, meaning that only plants with a heat component would qualify. A number of biomass plants have been proposed in Western Massachusetts, but developers find it difficult to build them near industrial plants that could make use of large amounts of heat.

The regulations, which the state legislature is now considering, would also limit wood used in biomass plants to residue from logging operations, like tree tops and branches, rather than whole trees, and require that a sufficient amount of biomass remain in the forests to support the local ecosystem.

Ultimately, the main issue being debated is whether burning trees can be considered carbon neutral. The biomass industry argues that, because trees absorb carbon as they grow, burning them remains carbon-neutral as long as more trees are planted and forests are managed sustainably. But some environmentalists point to studies reporting that, under some scenarios, wood-burning biomass plants can increase carbon emissions for decades even if they replace fossil fuels.

Photo credit: Duncan Brown (cradlehall)/Flickr