Elsevier

Biomass and Bioenergy

Volume 83, December 2015, Pages 32-41
Biomass and Bioenergy

Research paper
Cellulosic ethanol production: Landscape scale net carbon strongly affected by forest decision making

https://doi.org/10.1016/j.biombioe.2015.08.002Get rights and content

Highlights

  • We survey non industrial private forest owners in Michigan.

  • We create and apply a new model of carbon accounting for bioenergy in Michigan.

  • 47% of forest landowners would harvest trees as a bioenergy feedstock.

  • Cellulosic ethanol production has a small positive carbon balance.

  • Forest growth with no harvest has a much greater positive carbon balance.

Abstract

In producing cellulosic ethanol as a renewable biofuel from forest biomass, a tradeoff exists between the displacement of fossil fuel carbon (C) emissions by biofuels and the high rates of C storage in aggrading forest stands. To assess this tradeoff, the landscape area affected by feedstock harvest must be considered, which depends on numerous factors including forest productivity, the amount of forest in a fragmented landscape, and the willingness of forest landowners to sell timber as a bioenergy feedstock. We studied landscape scale net C balance by combining these considerations in a new, basic simulation model, CEBRAM, and applying it to a hypothetical landscape of short-rotation aspen forests in northern Michigan, USA. The model was parameterized for forest species, growth and ecosystem C storage, as well as landscape spatial patterns of forest cover in this region. To understand and parameterize forest owner decision making we surveyed 505 nonindustrial private forest (NIPF) owners in Michigan. Survey results indicated that 47% of these NIPF owners would willingly harvest forest biomass for bioenergy. Model results showed that at this rate the net C balance was 0.024 kg/m2 for a cellulosic ethanol system without considering land use over a 40 year time horizon. When C storage in aggrading, nonparticipating NIPF land was included, net C balance was 1.09 kg/m2 over 40 years. In this region, greater overall C gains can be realized through aspen forest aggradation than through the displacement of gasoline by cellulosic ethanol produced from forest biomass.

Introduction

The future development of industrial scale production systems for cellulosic ethanol could help meet the renewable energy goals of the Energy Independence and Security Act (EISA) of 2007. This legislation mandated that in the USA 49.0 million m3 of renewable fuel would be blended with gasoline by 2010 and 136 million m3 of renewable fuel would be blended into gasoline by 2022. These renewable fuels were mandated to include 60.6 million m3 of advanced biofuel production, including cellulosic ethanol [1]. Biofuels are included in the Act because grasses and woody crops fix carbon (C) as they grow, and the displacement of fossil fuels with ethanol from biomass has the potential to lower net C emissions over the cycle of plant growth, fuel conversion, and combustion.

However, woody biomass sources like forests also play a large role in the global scale exchanges of C between the land and the atmosphere and have the potential to mitigate the effects of rising atmospheric CO2 by removing atmospheric CO2 and storing C as forests aggrade [2], [3]. If forests are left to aggrade, C accumulates not only in the wood growth but also in the annual production of foliar and fine root litter. Through ecosystem processes that limit decomposition or stabilize C in soil, forest floor and soil C pools continue to increase at high rates for decades after initiation of a new forest stand [4], [5], [6]. Many strategies are being assessed to manage forest C balance at scales from individual forest stands to large regions. These include reforestation, avoided degradation and deforestation, forest aggradation (unharvested growth), and silvicultural management to promote forest C storage [7].

In this context, if a biomass fuel system relying on forest biomass is considered as a strategy for mitigating rising atmospheric CO2, it is worthwhile to compare the proposed biomass fuel system against the aforementioned other potential uses of forests to mitigate rising atmospheric CO2 [8], [9]. However, to rigorously assess such life cycle net C gain of a biomass fuel system, careful definition of system boundaries is needed, including conceptual, spatial, and temporal boundaries. One such choice of boundary is to include the C balance associated with the land use for land on which the feedstock is produced. This has been a controversial topic in the assessment of net C emissions from biofuel systems [10], [11], [12], [13], [14].

Other considerations, such as the constraints on ethanol biorefineries must be taken into account when judging the effectiveness of cellulosic ethanol as a C mitigating option. For an industrial scale biorefinery to obtain forest biomass much of the feedstock would need to come reliably from landowners over a series of harvest rotations. This need for supply puts small forest landowners in an important position. The more feedstock they are willing to harvest and sell, the lower the distances over which biomass must be transported to fuel the biorefinery. The larger the size of a biorefinery, the greater flow of biomass needed, thus the area over which biomass needs to be transported scales directly with biorefinery size [15], [16]. In economic terms, this is a negative return to scale because average transport costs increase with distance. It is also likely to be a negative return to scale for C emissions because this transportation requires energy (and thus C emissions). Small forest landowners with a history of selling their wood to pulp mills or to other wood industries in decline would be in a good position to benefit from and support the success of the cellulosic ethanol industry, and, in conjunction, the EISA mandate [1], [15], [16], [17]. If these landowners are concentrated in sufficient numbers near the biorefinery, they could also help to minimize economic costs for a biorefinery [18]. Yet, a growing number of private forest landowners in the north central USA are choosing to make management decisions geared toward aesthetics and recreation, maintaining their growing forests, rather than harvesting for timber sales [19].

A novel aspect of our analysis is that we address forest management decision making by forest landowners, specifically nonindustrial private forest (NIPF) owners in northern Michigan, in relation to cellulosic ethanol production. In our analysis, willingness to harvest trees for feedstock affects both the distance over which biomass is transported and the amount of aggrading forest that remains within the transport radius. We addressed the following research question: To what extent are NIPF owners in northern Michigan willing to harvest their forests for bioenergy feedstock, and how do different levels of such private biomass sales impact the system net C balance of an industrial scale biorefinery?

Here we also address an important aspect of the land use and renewable fuels debate by comparing the net C balance of a cellulosic ethanol system from forest biomass at the landscape scale versus forest aggradation as an alternative in the identical landscape. Many analyses in the current literature address the question of how effective, from either a C or an economic perspective, is a given biofuel or C sequestration policy [20], [21], [22], [23], [24], [25], [26], [27]. A second question we indirectly address here is stated differently: How does overall net C balance compare in the uses of forest land for either aggradation or rotation harvests for biofuel feedstock, when both the biofuel production system and feedstock source area are considered at the appropriately large spatial scale and relevant time horizon? Such place based analyses have been done before as a way to assess the land use impact of a particular biofuel production chain [13].

Section snippets

Scope of the project

We focus on forested landscapes and ecosystems of northern Michigan, USA, which includes the Upper Peninsula and the northern areas of the Lower Peninsula. We consider a hypothetical, industrial scale, cellulosic ethanol biorefinery that would use forest tree biomass from short-rotation aspen forests in this region as its feedstock. The model does not intend to capture the full diversity of forest stands over northern Michigan, nor does it try to capture all silvicultural methods available or

Survey of nonindustrial private forest owners

Of the 1203 copies of the survey instrument mailed, 106 were returned undelivered and 505 were returned with responses, yielding an effective response rate of 46%. The land area managed by the NIPF owner respondents was concentrated in Michigan's Upper Peninsula (Fig. 1). When asked about the purposes for which they used their forest land, 82% responded that they used the land for hunting, fishing or trapping; 70% used the land for conservation purposes; 69% used the land for timber or firewood

Cellulosic ethanol

Several previous studies have emphasized the importance of considering land use or land use change and its effects on C accounting when assessing net C emissions related to biofuel production. Melillo et al. [54] used a combination of economic and terrestrial bioscience models to predict the impact of future potential expansion of biofuel production. As anticipated demand for biofuels increased it was predicted that unused, forested land would be converted for biofuel production. Searchinger

Conclusions

In Michigan, the willing participation rate of NIPF owners to harvest trees as a feedstock for cellulosic ethanol was quantified to be 47%. At this rate, over a 40 year period, the cellulosic ethanol biorefinery has a positive system NCB of 0.024 kg/m2, when averaged over the feedstock source area but not including ecosystem C balance in the source area landscape (Table 1). Our sensitivity analysis revealed that changes to biorefinery technology and the energy needed to control moisture content

Acknowledgments

We are grateful to the hundreds of survey respondents who provided critical information on their decision making for private forest management and sales of forest biomass. Valuable feedback from Sarah Kiger, Jason Martina, Seta Chorbajian, Lisa Fouladbash, and three anonymous reviewers helped focus and improve our research questions and analysis. This research was partially funded by the School of Natural Resources and Environment at the University of Michigan and by a U.S. Forest Service

References (62)

  • B. Bolin et al.

    Global perspective

  • Y. Pan et al.

    A large and persistent carbon sink in the world's forests

    Science

    (2011)
  • R.D. Yanai et al.

    Soil carbon dynamics following forest harvest: an ecosystem paradigm reconsidered

    Ecosystems

    (2003)
  • C.A. Johnston et al.

    The frontier below: carbon cycling in soil

    Front. Ecol. Environ.

    (2004)
  • A. Lindauer-Thompson

    Incorporating Carbon Storage into Forest Management in Michigan: a Modeling Based Scenario Analysis

    (2008)
  • M.G. Ryan et al.

    A Synthesis of the Science on Forests and Carbon for U. S. Forests [Internet]

    (2010)
  • D. Lindenmayer et al.

    Six principles for managing forests as ecologically sustainable ecosystems

    Landsc. Ecol.

    (2013)
  • J. Fargione et al.

    Land clearing and the biofuel carbon debt

    Science

    (2008)
  • T. Searchinger et al.

    Use of US croplands for biofuels increases greenhouse gases through emissions from land-use change

    Science

    (2008)
  • Y. Yang et al.

    Marginal yield, technological advances, and emissions timing in corn ethanol's carbon payback time

    Int. J. Life Cycle Assess.

    (2015)
  • J. Liu et al.

    Systems integration for global sustainability

    Sci

    (2015)
  • T.G. Knoot et al.

    The changing social landscape in the Midwest: a boon for forestry and bust for oak?

    J. For.

    (2009)
  • M.R. Schmer et al.

    Net energy of cellulosic ethanol from switchgrass

    Proc. Natl. Acad. Sci. U. S. A.

    (2008)
  • J. Hill et al.

    Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels

    Proc. Natl. Acad. Sci. U. S. A.

    (2006)
  • I.E.A. Bioenergy

    Sustainable Production of Woody Biomass for Energy: a Position Paper Prepared by IEA Bioenergy [Internet]

    (2003)
  • J. Bowyer et al.

    Bio-energy: momentum is building for large scale development [Internet]

    (2005)
  • A.E. Farrell et al.

    Ethanol can contribute to energy and environmental goals

    Science

    (2006)
  • S. Gonzáles-García et al.

    Environmental assessment of black locust (Robinia pseudoacacia L.)-based ethanol as potential transport fuel

    Int. J. Life Cycle Assess.

    (2011)
  • D. Pimentel et al.

    Ethanol production using corn, switchgrass, and wood; biodiesel production using soybean and sunflower

    Natl. Resour. Res.

    (2005)
  • Cited by (9)

    • Land use for bioenergy: Synergies and trade-offs between sustainable development goals

      2022, Renewable and Sustainable Energy Reviews
      Citation Excerpt :

      A total of 134 peer-reviewed studies were found through the systematic literature search. However, studies that focused on agricultural residues were excluded [40–42], land use mapping [43–46], stakeholders’ perspectives and decision making [47–50], farmland services (e.g., dairy and poultry) [51–53] and review style studies [54–57]. Thus, in total only 59 studies fell within the scope of the study.

    • Agent-Based Modeling for bioenergy sustainability assessment

      2019, Landscape and Urban Planning
      Citation Excerpt :

      Although biomass can be obtained using selective harvesting techniques that remove overgrowth and improve environmental sustainability, when an integrated harvest is required, increased harvesting often leads to soil degradation as well as biodiversity, habitat, and wildlife losses that reduce environmental sustainability overall (Dale et al., 2013). Removing biomass from a landscape also reduces its carbon sequestration capacity and can nullify the climate change advantages of bioenergy over conventional fossil fuels (Brunner, Currie, & Miller, 2015). Increased harvesting can also introduce land-use conflicts among individual landowners and across the landscape as a whole wherever harvesting conflicts with key reasons for using or owning forestland, such as preserving privacy barriers, natural aesthetics, wildlife habitat, recreational opportunities, or “letting nature take its course” (Becker et al., 2013; Lind-Riehl et al., 2015).

    • Family forest owners and landscape-scale interactions: A review

      2019, Landscape and Urban Planning
      Citation Excerpt :

      Although this subcluster most closely aligned with the forest ownership cluster (#10), I will discuss these four nodes as a separate subcluster here. Sourcing renewable energy in ways that are carbon neutral and economically feasible requires woody biomass harvesting close to points of production or use (Brunner, Currie, & Miller, 2015; Creutzburg, Scheller, Lucash, & Evers, 2016; Wear & Greis, 2013). Given the large percentage of forested landscapes under family forest owner control, the availability of this woody feedstock for energy production naturally requires harvesting family-owned forests (Cai et al., 2016).

    View all citing articles on Scopus
    View full text