From an Associated Press article by John Flesher in The Mining Journal (Marquette, Michigan):

PARK FALLS, Wis. – Forests are a treasure trove of limbs and bark that can be made into alternative fuels and some worry the increasing trend of using that logging debris will make those materials too scarce, harming the woodlands.

For centuries, forests have provided lumber to build cities, pulp for paper mills and a refuge for hunters, fishers and hikers. A flurry of new, green ventures is fueling demand for trees and the debris leftover when they are harvested, which is called waste wood or woody biomass.

”There simply is nowhere near enough waste wood for all of these biomass projects that are popping up all over the place,” said Marvin Roberson, a forest policy specialist with the Sierra Club in Michigan.

Waste wood has become a sought-after commodity, prompting concerns that the demand might overwhelm supply and damage the ecosystem. But government officials say there’s plenty available and they point to guidelines that are aimed at maintaining tree debris to give the soil nutrients.

Many biomass projects are tied to the forests that extend across Minnesota, Wisconsin, Michigan and part of Ontario. Among them is Flambeau River Papers, a mill in Park Falls, Wis., that emerged from bankruptcy three years ago and is pinning its hopes for profitability on generating its own heat with woody biomass.

In another Wisconsin town 50 miles away, a power company is switching from burning coal to producing combustible gas from logging leftovers. And in Michigan’s neighboring Upper Peninsula, a plant under development called Frontier Renewable Resources will convert timber into 40 million gallons of cellulosic ethanol a year.

Researchers led by University of Minnesota forest expert Dennis Becker reported this summer that many would-be investors are uneasy about supplies of waste wood.

They fear environmental reviews and litigation could make some public woodlands unreliable sources, particularly in the West, where most forest lands are under federal ownership and logging often raises legal tussles, the report said.

Another problem with woody biomass is that much of the supply is in protected areas, or so far from markets that removing and transporting it would be too expensive, Becker said.

He led a separate study that found a realistic estimate of biomass available in Michigan, Minnesota and Wisconsin was 4.1 million tons a year. Annual demand soon could reach 5.7 million tons, it said.