UVM Theses and Dissertations
Format:
Print
Author:
Mika, Anna M.
Dept./Program:
Natural Resources
Year:
2013
Degree:
Ph. D.
Abstract:
There is debate about the most effective mitigation strategies for reducing atmospheric concentrations of carbon dioxide (CO₂). Forests are important carbon (C) sinks that sequester atmospheric CO₂ and store it in living and dead parts for decades. However, wood can also be burned for energy ("bioenergy") and is currently considered a C-neutral (i.e. no net emissions) energy source. The controversial debate about best use of forests for CO₂ mitigation has centered on the trade-off between allowing trees to sequester C and harvesting them for energy generation.
In this body of work, I (1) created a tool for regional planners that estimates the impacts of development scenarios on terrestrial C sinks and CO₂ emissions; (2) used field data to assess the impacts of bioenergy on short-term CO₂ emissions; and (3) modeled the effects of bioenergy on long-term landscape CO2 flux when harvests are staggered temporally and spatially. I conclude that high density development that reduces reliance on transportation and does not remove C sinks, such as wetlands and forests, has the best CO₂ outcomes. Field data showed that whole-tree harvesting, where the tree tops are removed and chipped for bioenergy, may reduce forest C pools and result in greater CO₂ emissions.
This practice was associated with more intense skidding machinery and siiVicultural treatments. In the long-tenn, modeling showed that although 82% of stands harvested for bioenergy had a positive net cumulative C flux (i.e. storage), the average landscape C flux relative to nonbioenergy was negative. Allowing some stands to grow while others are harvested and including avoided fossil fuel emissions may offset emissions from bioenergy harvests. The conclusion depended on maintaining post-harvest basal areas consistent with silvicultural guidelines. Reducing or removing minimum stocking resulted in further net landscape CO₂ emissions. These three studies demonstrate the importance of maintaining terrestrial C sinks for climate change mitigation.
In this body of work, I (1) created a tool for regional planners that estimates the impacts of development scenarios on terrestrial C sinks and CO₂ emissions; (2) used field data to assess the impacts of bioenergy on short-term CO₂ emissions; and (3) modeled the effects of bioenergy on long-term landscape CO2 flux when harvests are staggered temporally and spatially. I conclude that high density development that reduces reliance on transportation and does not remove C sinks, such as wetlands and forests, has the best CO₂ outcomes. Field data showed that whole-tree harvesting, where the tree tops are removed and chipped for bioenergy, may reduce forest C pools and result in greater CO₂ emissions.
This practice was associated with more intense skidding machinery and siiVicultural treatments. In the long-tenn, modeling showed that although 82% of stands harvested for bioenergy had a positive net cumulative C flux (i.e. storage), the average landscape C flux relative to nonbioenergy was negative. Allowing some stands to grow while others are harvested and including avoided fossil fuel emissions may offset emissions from bioenergy harvests. The conclusion depended on maintaining post-harvest basal areas consistent with silvicultural guidelines. Reducing or removing minimum stocking resulted in further net landscape CO₂ emissions. These three studies demonstrate the importance of maintaining terrestrial C sinks for climate change mitigation.