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Carbon Balance of Forest Thinning and Bioenergy Production



Author:

Katharine C.  Kelsey
Department of Biology
University of Alaska Anchorage
kathyckelsey@gmail.com

Abstract:

This interrupted case study introduces students to the concept of carbon storage and how land management decisions can affect this vital ecosystem service.  Forests play an important role in the carbon cycle because of their ability to uptake and store large amounts of carbon and their potential to release carbon to the atmosphere following forest disturbance or management. Students are asked to evaluate the carbon balance of a forest treatment in which harvested biomass is used for bioenergy electricity generation. Through readings and in-class discussions, students consider the effects of past and current management practices on western forests, predict future forest carbon storage under varying management scenarios, and finally evaluate the economic and ecological consequences of bioenergy electricity production in order to make a recommendation for future forest management in this region. Designed for an upper division undergraduate ecosystem management course, the case would also be appropriate for any upper division ecology course in which biosphere-atmosphere interactions, ecosystem management, or forest carbon storage is discussed.

Objectives:
  • Recognize the effects of fire exclusion on ponderosa pine forest structure in the American southwest and explain the justification for silvicultural treatments in these forests.
  • Predict future forest carbon storage under varying scenarios of forest treatment and wildfire.
  • Combine different types of information to determine the carbon balance of forest treatments and subsequent bioenergy electricity production.
  • Evaluate the ecological and economic consequences of forest treatment and energy production to make a recommendation to the Forest Service.
Keywords: Ecosystem management; forest carbon; bioenergy; carbon emissions; carbon storage; carbon balance; forest management; forest treatment; Western US; climate change mitigation
Topical Area: N/A
Educational Level: Undergraduate upper division
Formats: PDF, PowerPoint
Type/Method: Interrupted
Language: English
Subject Headings: Ecology   Environmental Science   Forestry   Natural Resource Management  
Date Posted: 5/7/2015
Date Modified: N/A
Copyright: Copyright held by the National Center for Case Study Teaching in Science, University at Buffalo, State University of New York. Please see our usage guidelines, which outline our policy concerning permissible reproduction of this work.

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Supplemental Materials


The PowerPoint presentation (link below) can be used to introduce the case in class.

  Classroom PPT Presentation
Thanks for providing an interesting case study about forest management and the carbon cycle. I used this case study with my non-majors forest biology course this week. We had a great discussion of the Hurteau paper and parts I and II of the case study. However, today, as we were working through Part III, my students came up with some questions that I was unable to answer based on the materials. We were especially confused by question 3. Does the Forest Vegetation Simulation model assume that all of the carbon in the thinned trees go into the atmosphere immediately? If so , I can see why the 9.7 Mg C/ha would be subtracted from the cumulative carbon exchange. My students, however, pointed out that we have no reason to think that all that carbon from the thinned trees would be contributed to the atmosphere immediately, unless it was used in bioenergy production. If the carbon in the thinned trees is stored in lumber, rather than emitted, you could imagine that using bioenergy would add ~9.7 Mg C/ha to the cumulative carbon exchange. Could you please help us out by clarifying the assumptions of the model? Thanks!


Val Brenneis
Biology/ESR
Portland Community College
Portland, OR
valance.brenneis@pcc.edu
12/3/2015

Author Reply: Your students have keyed in on two important themes I always end up discussing when using this case: (1) the assumptions that go into using ecosystem models, and (2) the importance of timescale when calculating carbon balance.

For the purpose of this case study, the model assumes that woody material removed from the forest during thinning is a direct and immediate emission to the atmosphere. If this woody material is mulched or burned in a controlled burn, then this is a reasonable assumption. But, if the woody material is stabilized in lumber, like your students suggested, then the issue is more complicated. I explored this possibility—i.e., that some of the woody material is stabilized in lumber—in another paper on this topic (see the following 2014 article in Carbon Balance and Management: Short and long-term carbon balance of bioenergy electricity production fueled by forest treatments). However, the bottom line is that even if you do use the woody material for lumber, there is still a slight carbon benefit from bioenergy production over lumber. This is partly because a lot of woody biomass is lost to milling waste, and also because the thinned trees are small, so many of them are not big enough for use as lumber.

Another thing your students may wish to consider (especially because they are interested in the assumptions of the model) is, how well do the growth parameters in the model represent how forests will grow in the future, under different climate conditions? In the paper I referenced above, the results indicate that there is a carbon benefit to bioenergy electricity production. But, if climate conditions change the rate at which the forests grow and regenerate in the future, these results could look different.

Katharine C. Kelsey
12/4/2015













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