Harvesting wood debris from areas that have been clear-cut of timber does not affect the animals that live there, according to a study from researchers at N.C. State University.
Chris Moorman, a professor of forestry and environmental resources, and his students spent four years cataloging small animals such as mice, toads, bugs and mourning doves at loblolly pine plantations. They found that the populations in clear-cut sites were unaffected regardless of how much wood debris was removed.
This low-value wood, or “biomass,” left over from logging is pulverized to make wood pellets that are used as a carbon-friendly alternative to coal in Europe and in parts of the United States. Wood is classified as a renewable energy source by the European Union, which burns wood pellets from the southeastern U.S. to comply with the Kyoto Protocol to curb greenhouse gas emissions.
The biomass left after a forest has been clear-cut supports a host of critters. It is home to bugs at the bottom of the food chain, which are eaten by burrowing shrews and amphibians and small reptiles such as salamanders. Some of the biomass is a fertilizer for smaller vegetation that feeds birds and rodents. The cold-blooded citizens of the sites make their homes in the wet, woody debris left by logging.
Moorman and his students wanted to know if removing large amounts of this biomass to make wood pellets could hurt the communities that spring up after the lumber is chopped down.
Moorman says clear-cut logging has a well-known effect on biodiversity by displacing forest-dwellers such as deer and nesting birds. Less understood was the effect of clearing the debris left after logging. Ecologists have predicted that harvesting biomass would remove potential habitats and sources of food from clear-cut areas, causing animal populations to fall.
Sarah Fritts, an ecologist who studied the mammals, amphibians and reptiles at the logging sites, speculated that toad populations would be lower in areas where more wood debris was harvested. But after four years of research, she says, she “captured thousands and thousands of toads,” and there was no variation even in the most harvested sites.
The 150-acre pine plantations in the study have so much wood debris left over after logging that even the most heavily harvested sites were left with 10 percent of their biomass, Moorman said. The harvesters start to lose money if they chase down every last branch and pile of wood chips, some of which are water-damaged and would not make good wood pellets anyway. Even 10 percent of the debris is enough to satisfy the population that survives after clear-cutting.
To count the populations at each site, Fritts set live traps and put a tag on each animal so it would not be counted again. She was curious about why the toads were not as affected by a lack of debris as she hypothesized.
To find out what they preferred, she built a 30-square-foot rink divided into four sections, each with different amounts of biomass. The quarters were separated by low current electrical wire that would track when it was crossed by the toads Fritts kept in the box. She found that during the day, toads spent their time in the debris because it retains water and shielded them from the sun. When it cooled off at night, the toads ventured out to find food.
According to Moorman, the animals that live in clear-cuts “evolved to respond to disturbances.” Forest clearing events like forest fires and hurricanes are even more destructive than logging, and the populations in coastal North Carolina are resilient. Moorman noted the study may not apply to biomass harvesting in logging sites in the mountains.
Stephen Ginley: 919-829-4520