I don't think they get involved in the small picture......which most of that stuff is. They are busy with really big stuff like Coal to Gas, Coal to Fertilizer, etc....
Their concerns are on three angles - bad mining practices, pollution output and...of course...CO2!
I guess they take each case individually...in general they approve of clean and sustainable biomass...if it is needed:
http://www.sierraclub.org/coal/oh/resources/burger_resources.asp
Here are some of their guidelines. But these are all moving targets. The Club is really the members. The members are each local state chapter, etc.
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Sierra Club position
Sierra Club does not support using whole trees or logging waste (branches, forest floor material) directly from forests in biomass plants, except those from privately owned tree farms that did not recently replace natural forests. This material is needed to replenish soil nutrients, in ways that do not increase fire risk. Biomass operations often scrape every stick and blade of grass from the soil, causing erosion and leaching soils.
We do not oppose using marginal agricultural land for farms of hybrid trees. This type of farming uses less chemicals than corn or soybean agriculture and creates less stream turbidity. The Sierra Club is opposed to use of transgenic trees in plantations or natural forests because of the risks to native trees and ecosystems.
Sierra Club does support use of wood waste from mills. Any “biomass residue wood, sawdust, bark, chipped wood, or brush;” (216B.2424 subd. 5(e)(2)) or “waste wood, including chipped wood, bark, brush, residue wood, and sawdust” (216B.2424 subd. 6(f)) used in biomass plants should be mill waste, not harvested or salvaged from logging operations.
Where applicable, Sierra Club does not support use of recyclable waste paper in biomass plants or municipal incinerators.
The Sierra Club notes that crop residues have a role in maintaining soil fertility and structure and their removal for use as a fuel is not without significant impacts. Depriving soil of these nutrients may necessitate greater use of pesticides and chemical fertilizers, potentially canceling any environmental or economic benefit of using agricultural wastes as biomass. The use of pesticides and drainage technologies to grow crops have created significant environmental impacts and fuel use of crop residues would provide market incentives to increase these impacts. Crops grown specifically for fuel would have to be evaluated for their pesticide and soil productivity impacts on a case by case basis.