Michigan growers of apples and cherries are doing a pretty good job environmentally when it comes to greenhouse gas production.
Where they falter is with disposal of damaged or dead trees, says Jim Flore, a Michigan State University horticulture professor in East Lansing.
Although the research is still preliminary, the carbon footprint could be improved by burning discarded trees in a boiler to produce power rather than burning them in the open field or taking them to a landfill, Flore says.
"We have [fruit] processing plants up and down the state, especially in the west, that are mainly fueld by natural gas," he says. "What this might do is be beneficial for them to use [the the trees for fuel] rather than burn them.
"I think there might be enough to make it feasible for some of the bigger co-ops, but we aren't quite at that point yet."
Along with Flore, Dan Keathley, a Michigan State University forestry professor, is looking at the feasibility of planting fast-growing hybrid poplars on part of an orchard.
In years where the grower may be removing just a few fruit trees to reset, the theory is the poplars could be harvested to produce enough biomass to generate power.
Flore says initial calculations show most apple and cherry orchards have a positive carbon footprint, meaning they store more carbon than they emit.
He led a team that examined how much carbon dioxide, a greenhouse gas, the fruit trees pull from the atmosphere and store in their tissues as carbon.
There are two ways to calculate that, Flore says.
One uses a carbon supply and consumption budget developed by Alan Lasko, a professor of plant physiology at Cornell University in Geneva, N.Y.
The other measures dry matter in trees and relates it to a cross section of the trunk.
By plugging trunk size measurements and trees per acre into a spreadsheet, growers are able to roughly calculate the orchard's carbon footprint, Flore says.
The researchers only looked at the carbon emitted and sequestered during crop production activities.
They didn't include the amount of carbon in the fruit, since that is harvested and removed from the orchard.
Based on conversations with the Chicago Climate Exchange, which deals in carbon offset credits, he says they also didn't include carbon emitted during transportation or to produce fertilizer or pesticides in their calculations.
"The big question is, where do you start and where do you stop?" Flore asks. "I don't want to make too much out of the carbon footprint, and it just depends on how you make the calculations. I think growers are fairly environmentally sound, and it's very close to break even."