Finding better methods of carbon management and optimal use of forest biomass are the subjects of four research projects currently being conducted by scientists in the University of Arkansas at Monticello’s School of Forest Resources. The projects include a study of agroforest systems for bioenergy crop production by Hal Liechty, Matthew Pelkki and Donald White; a comparison of feedstocks grown with and without fertilization by Jamie Schuler; the characterization of in-forest woody biomass by Pelkki; and an evaluation of carbon market financial returns by Pelkki and Schuler.
All four projects were recently recognized by the Southern Forest Research Partnership’s “Forestry Research In The South” newsletter.
The first project’s goal is to develop economically and ecologically sustainable agroforest systems for producing bioenergy crops on what is termed marginal agricultural land in the lower Mississippi Valley. Liechty, Pelkki and White have created sites containing pure stands of cottonwood trees and switchgrass as well as alley cropped mixtures comprised of swaths of either all trees or all switchgrass in strips 15 to 30 meters wide. “The alley cropped sites contain a mixture of two species,” explains Pelkki, “but in strips wide enough to plant and run machinery through.”
The sites are located at the UA Division of Agriculture Research Station near Brinkley, the Southeast Research and Extension Station at Rohwer, and at a site near Archibald, La., in cooperation with the LSU Agriculture Center. All three sites are on soil classified as having low potential for growing traditional row crops.
Pelkki, White and Liechty are studying the amount of biomass produced on each site and the characteristics of the fuel obtained from the biomass as well examining carbon sequestration, which is the storage of carbon in living plants above and below ground and also the carbon that is mineralized by microorganisms in the soil when decaying plant material are digested for food.
The scientists will also monitor all greenhouse gas emissions from establishing, maintaining and harvesting the sites. “We will use life cycle analysis to monitor the carbon emissions from the production of all inputs into the site, including seed, fertilizer and herbicides, as well as carbon emissions and energy savings from the biofuel produced by the site,” says Pelkki.
The second project, a comparison of feedstocks grown with and without fertilization, focuses on short rotation woody crop (SWRC) production systems. With interest growing for converting marginal agricultural lands to SRWC sites, Schuler began a study in 2009 to compare various species for growth rate. Schuler established plots of black willow, eastern cottonwood, and American sycamore trees, some with and some without fertilization. Trees were planted at intervals of eight feet and measured for diameter, height, above ground biomass, and coarse and fine root biomass. Schuler is also examining soil carbon on each plot.
According to Schuler, preliminary results after one year showed the American sycamore achieved the greatest above ground biomass on both fertilized and unfertilized plots, and that fertilization had a positive, but not significant, impact on above ground biomass.
In the third study, Pelkki examined the energy potential of in-forest residues, or logging slash (the part of trees left in the woods after traditional logging) at three harvesting sites in south Arkansas. Pelkki studied the particle size distribution, moisture content, Btu value (the heat energy contained in wood when it is oven dry) and ash content (the amount of unburnable minerals and other waste left after full combustion) of forest biomass resulting from two chipping and three grinding operations. “Ash content is important because ash can buildup in boilers during combustion, requiring cleaning and maintenance,” Pelkki explains. “It also increases particulates when emitted from smokestacks and is a waste product that needs to be disposed of, sometimes requiring a landfill if there are heavy metals contaminating it.”
Pelkki’s study found that the in-forest residue contained a moisture content of 87 percent (meaning a piece of wood that weighs 100 pounds oven dry weighs 187 pounds in the forest), a Btu value of 7,945 per pound, and a 3.1 percent ash content.
In the final study, Pelkki and Schuler are studying the financial impacts of carbon sequestration on three different models of pine management – uneven-aged, natural even-aged, and plantation. The study looks at pulpwood and saw timber yields and carbon sequestration rates for above and below ground live carbon as well as carbon stored in long-lived wood products. The importance of the study, says Pelkki, is in the financial value of carbon for forest landowners and the complicated carbon trading rules established by state and federal authorities.
“Let’s say you have a forest and it is measured for live biomass by a forester to determine the amount of carbon in the forest,” Pelkki explains. “As a landowner, you only get to sell what you grow, so every five years, the biomass of your forest is measured. The amount of growth in carbon is what you can sell. So if a forest today has 50 tons of CO2 equivalent in its biomass, and next year, it has 58 tons, the growth is eight tons of CO2, and that is what you can sell.
“The forester now certifies that you have eight tons of carbon to sell, and this is now certified as eight tons of carbon credits and is put up for sale, just like any futures commodity, on a carbon exchange or carbon market. Let’s say a California power company has burned coal and exceeded the limits for carbon emissions set by California law. This company needs to buy carbon credits, so it bids for the right to buy the landowners eight tons of carbon credits, and just like orange juice futures, the high bidder gets the eight tons of carbon credits so it isn’t fined by the state of California for exceeding its carbon allowance.”
According to Pelkki, preliminary results from the study show that carbon markets can provide added value to all forms of pine management, with additional returns of $136 per hectare (2.471 acres) for uneven-aged stands, $400 per hectare for natural even-aged stands, and $672 per hectare for pine plantations.
For more information, contact the School of Forest Resources at (870) 460-1052.