Chomping at the Bit
Clearing underbrush in the forest of North Carolina's coastal plain can cost between $500 and $1,000 per acre, according to Joseph Roise, a professor of forestry at North Carolina State University. Mechanically clearing mesquite that infests millions of acres of Texas rangeland has a similar cost, says Jim Ansley of Texas A&M University's Research and Extension Center. Finding a way to reduce those costs is why both men are working on equipment to automate the harvest of small-diameter trees for wildfire prevention and wildlife habitat development, as well as the collection of biomass feedstocks.
Although their goals are similar, the two projects face significantly different challenges. Roise is trying to develop a machine that can chew through underbrush while not sinking into the perpetually wet, boggy soil-called pocosin-that dominates the North Carolina coastal plain. Ansley's goal is to develop a collector that can handle the remains of mesquite mechanically harvested by a commercial mulching machine. The size of the pieces that he is trying to collect ranges from a few inches to three feet long and are six inches in diameter. Both projects have completed and tested prototypes, but there is a lot more work to be done before the harvesting machines will be ready for commercialization.
Roise says NCSU will start testing a second-generation prototype of its harvester this summer. He believes the new machine will be much more efficient at harvesting biomass than the current model. "We saw all the problems [with the first model], and we know a lot of ways to correct those," he says. "So we are putting that in a new design. This truly is research because we are testing this equipment under many sets of parameters. Hopefully that research will lead to a better second generation."
Ansley says the Texas biomass collector worked in trials but wound up leaving too much wood on the ground. He believes that if the equipment can pick up between 60 percent and 70 percent of the wood, it will make collecting mesquite for biomass production economical. So far, the prototype can collect approximately 40 percent of mesquite mulch. Ansley is seeking further funding to make improvements on his design. "Until we get more funding, we aren't going to make much more progress," he says. "In addition, we will be looking at the ecological impact of employing such a harvesting system."
Both men say the resources they are looking to harvest are unlikely to be large enough to fuel large-scale biorefineries on their own. However, clearing brush is vital in order to reduce fire hazards, and improve wildlife habitat and rangeland, and these machines could provide an important supplemental feedstock to a cellulosic ethanol industry fueled by timber waste or energy crops. "This is a biomass source that is somewhat on the fringes," Ansley says. "It isn't a mainline source like corn or switchgrass. [Mesquite] occurs in areas where we have depressed rural communities, and one reason they are depressed is that mesquite has invaded and hurt the livestock industry. So there is a lot of grassroots interest in taking this pest or weed-however you want to look at it-and turn it into something that has some value."