Whole-tree harvesting could boost biomass production
In the first study, the researchers examined the effect of residue removal on understory plant communities rather than allowing the residue to decompose and theoretically provide nutrients to the herbaceous and shrubby vegetation underneath the tree canopy.
In the second study, Premer, Froese and Vance delved deeper into an effect they noticed while the study was underway: “Cut to length” logging systems used intentionally to reduce soil compaction might not be effective in this regard, creating long-lasting patterns of reduced growth within regenerating stands.
The third paper examines the persistence of residues and differences in carbon sequestration and macronutrients between sites where residues were removed and where they were retained. Collectively, the three papers address site impacts in Great Lakes aspen forests and demonstrate that residue removal has few effects on forest ecology in managed stands.
“It seems obvious: logging, especially when tops and branches are removed for bioenergy production, must remove nutrients and wood that should remain to nourish the regenerating forest. So Midwestern states adopted guidelines for forest biomass harvest to protect forest lands,” Froese said. “We studied the difference in soil nutrients, carbon and the rate of growth of regenerating aspen forests in the upper Midwest and we found there is no difference in aspen stand productivity when whole trees are removed. It turns out branches just don’t appear to play much of a role in the ecology of aspen forest productivity after all.”
Operating under a mistaken assumption, Midwestern states adopted guidelines to protect soils and ecosystems without really understanding the need for guidelines. This action has added complexity and cost, which disincentivize the adoption of bioenergy.
“The states’ actions convey the notion that all biomass removal is ‘damage’ and therefore we must limit the ‘damage’ to some level that we can tolerate,” Froese said. “It may be that recovering biomass doesn’t damage the forest at all. If it reduces fossil fuel use, it may contribute to reducing damage to the global climate.”
Froese adds that despite its moniker, whole-tree logging doesn’t actually remove every last leaf and twig from the forest. Froese said in their study, 64% of residues remained despite trying to pick up as much of the logged study trees as possible.
The researchers sampled reforested aspen stands located in Baraga, Delta, Dickinson and Menominee Counties that are owned and actively managed by Weyerhaeuser Company (formerly Plum Creek Timber Company) and for which a 40-year commercial logging record exists, providing the scientists with a data set to verify against field measurements.
Materials provided by Michigan Technological University. Note: Content may be edited for style and length.