The Forest Service, United States Department 

of Agriculture (USDA), is dedicated to the 

principle of multiple use management of 

the Nation’s forest resources for sustained 

yields of wood, water, forage, wildlife, and 

recreation. Through forestry research, 

cooperation with the States and private forest owners, 

and management of the National Forests and National 

Grasslands, it strives—as directed by Congress—to provide 

increasingly greater service to a growing Nation.

The USDA prohibits discrimination in all its programs and 

activities on the basis of race, color, national origin, age, 

disability, and where applicable, sex, marital status, familial 

status, parental status, religion, sexual orientation, genetic 

information, political beliefs, reprisal, or because all or 

part of an individual’s income is derived from any public 

assistance program. (Not all prohibited bases apply to all 

programs.) Persons with disabilities who require alternative 

means for communication of program information (Braille, 

large print, audiotape, etc.) should contact USDA’s TARGET 

Center at (202) 720-2600 (voice and TDD).

To file a complaint of discrimination, write to USDA, 

Director, Office of Civil Rights, 1400 Independence 

Avenue, SW, Washington, D.C. 20250-9410, or call (800) 

795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal 

opportunity provider and employer.

Wood to Energy book cover.indd 1 
The Editors:

Christie Staudhammer, Assistant Professor, Forest Biometrics and Douglas 

R. Carter, Professor, Forest Economics and Management, University of Florida, 

School of Forest Resources and Conservation, Gainesville, FL 32611; L. Annie 

Hermansen-Báez, Technology Transfer Coordinator, U.S. Department of 

Agriculture Forest Service, Southern Research Station, Gainesville, FL 32611; 

Edward A. Macie, Regional Urban Forester, U.S. Department of Agriculture 

Forest Service, Region 8, Atlanta, GA 30309.

Product Disclaimer

The use of trade or firm names in this publication is for reader information and does not 

imply endorsement by the U.S. Department of Agriculture of any product or service. 

January 2011

Southern Research Station 

200 W.T. Weaver Blvd. 

Asheville, NC 28804
Wood to Energy: Using Southern 

Interface Fuels for Bioenergy

Edited by:

Christie Staudhammer, L. Annie Hermansen-Báez, 

Douglas R. Carter, and Edward A. Macie

Wood to Energy: Using Southern Interface Fuels for Bioenergy • iii

Contents

Page

Foreword .................................................................................................................................................................................................................................................... v

Chapter 1. Introduction to Woody Biomass Energy

Bioenergy and Woody Biomass Defined ................................................................................................................................................................................1

Importance of Woody Biomass as Energy .............................................................................................................................................................................1

History of Energy from Biomass Fuels .....................................................................................................................................................................................2

Trends in Population and Energy Use in the South ............................................................................................................................................................2

Trends in Land Use Change in the Wildland-Urban Interface ........................................................................................................................................3

Strategies in U.S. Energy Policy ..................................................................................................................................................................................................3

Social, Economic, and Environmental Benefits of Bioenergy .........................................................................................................................................3

Potential Negative Consequences of Biomass Energy Production in the Wildland-Urban Interface ..............................................................4

Conclusions.......................................................................................................................................................................................................................................5

References .........................................................................................................................................................................................................................................5

Glossary of Terms ............................................................................................................................................................................................................................7

Chapter 2. Woody Biomass Sources in the Wildland-Urban Interface

Introduction ......................................................................................................................................................................................................................................9

Forest Resources in the Wildland-Urban Interface .............................................................................................................................................................9

The Southern Forest Resource ...................................................................................................................................................................................................9

Forest Residues from Commercial Harvest ........................................................................................................................................................................ 11

Nonmerchantable Biomass from Silvicultural Activities ............................................................................................................................................... 12

Urban Wood Waste ...................................................................................................................................................................................................................... 12

Exotic Plant Removals, Native Plant Restoration, and Land Conversion ................................................................................................................. 14

Short-Rotation Intensively Managed Forests .................................................................................................................................................................... 14

Wood as a Fuel .............................................................................................................................................................................................................................. 15

Conclusions.................................................................................................................................................................................................................................... 15

References ...................................................................................................................................................................................................................................... 16

Glossary of Terms ......................................................................................................................................................................................................................... 18

Chapter 3. Harvesting, Preprocessing, and Delivery of Woody Biomass in the Wildland-Urban Interface

Introduction ................................................................................................................................................................................................................................... 19

Harvesting Woody Biomass ..................................................................................................................................................................................................... 19

Residue Harvesting ..................................................................................................................................................................................................................... 22

Environmental Issues ................................................................................................................................................................................................................. 23

Preprocessing Biomass .............................................................................................................................................................................................................. 24

Delivery Methods ........................................................................................................................................................................................................................ 25

Regulatory Issues ......................................................................................................................................................................................................................... 27

Conclusions.................................................................................................................................................................................................................................... 28

References ...................................................................................................................................................................................................................................... 28

Glossary of Terms ......................................................................................................................................................................................................................... 31
iv • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Chapter 4. Biomass Conversion to Energy and Fuels

Introduction ................................................................................................................................................................................................................................... 33

Background .................................................................................................................................................................................................................................... 33

Thermochemical Conversion of Biomass Fuel .................................................................................................................................................................. 33

Woody Biomass End Uses and Power Generation ........................................................................................................................................................... 40

Conclusions.................................................................................................................................................................................................................................... 46

References ...................................................................................................................................................................................................................................... 46

Glossary of Terms ......................................................................................................................................................................................................................... 48

Chapter 5. The Economic Availability of Woody Biomass

Introduction ................................................................................................................................................................................................................................... 51

Background .................................................................................................................................................................................................................................... 51

Methods .......................................................................................................................................................................................................................................... 52

Results .............................................................................................................................................................................................................................................. 59

Conclusions and Recommended Future Research .......................................................................................................................................................... 63

References ...................................................................................................................................................................................................................................... 63

Glossary of Terms ......................................................................................................................................................................................................................... 65

Chapter 6. Economic Impact Analysis of Woody Biomass Energy Development

Introduction ................................................................................................................................................................................................................................... 67

Case Studies of Wood-Fueled Power Plants ....................................................................................................................................................................... 68

Conclusions.................................................................................................................................................................................................................................... 76

References ...................................................................................................................................................................................................................................... 76

Appendix: Input-Output Analysis and IMPLAN Software/Databases for Economic Impact Analysis ........................................................... 77

Chapter 7. Public Perceptions of Using Wood for Fuel

Introduction ................................................................................................................................................................................................................................... 81

Public Perceptions of Biomass ................................................................................................................................................................................................ 81

Public Perceptions of Forest Sustainability ........................................................................................................................................................................ 82

Perceptions of Risk ...................................................................................................................................................................................................................... 83

Exploring Public Perceptions in Gainesville, FL ................................................................................................................................................................ 84

Providing Information and Engaging the Public ............................................................................................................................................................. 85

Summary ........................................................................................................................................................................................................................................ 86

References ...................................................................................................................................................................................................................................... 87

Editors and Authors ........................................................................................................................................................................................................................... 89
Wood to Energy: Using Southern Interface Fuels for Bioenergy • v

Foreword

Throughout the United States, a wide variety of efforts are 

underway to develop economically sound and environmentally 

sustainable bioenergy production systems. Several Federal 

policies, such as the Healthy Forests Restoration Act of 2003, 

support the establishment of biomass-to-energy systems. 

Scientists in government and nongovernmental agencies are 

taking the initiative to improve biomass production, processing, 

and conversion. Entrepreneurs are developing and marketing 

biobased products for use as bioenergy. Consumers are creating a 

demand for alternative forms of fuel and power generation. Yet, to 

advance biomass-based production, there is still a need to educate 

concerned citizens, community leaders, and those who can supply 

and use biomass fuels. Potential uses, sources of raw material, and 

requirements to convert from fossil fuels to biofuels are all topics 

of concern. 

The Southern United States (see figure below) produces nearly 

60 percent of the Nation’s wood, and projections show that this 

percentage will grow. Many southern forests are located in the 

wildland-urban interface (WUI), where increased human influence 

and land use conversion are changing natural resource goods, 

services, and management (Macie and Hermansen 2002). As 

populations increase and urban centers spread, large areas of 

once primarily contiguous forest land are increasingly influenced 

by humans and surrounded by or intermixed with urban 

development. The South is a prime location for producing woody 

biomass for energy production because of the proximity of forests 

to expanding urban areas, relatively low production costs, and an 

already abundant wood supply. 

The objectives of this document are to increase awareness of 

potential uses for biomass in WUI areas and to disseminate 

knowledge about putting bioenergy production systems in place, 

while addressing issues unique to WUI areas. The South’s WUI areas 

are expanding in population, making them well positioned to take 

advantage of emerging bioenergy production efforts. 

In WUI communities where both the necessary technology 

and adequate supplies of biomass are available, factors that 

inhibit immediate implementation of commercial biomass 

applications include limited awareness and knowledge about 

putting a biomass energy system in place, as well as a sense of 

uncertainty about the adequacy of biomass supplies and the costs 

of biomass sources relative to other energy sources. Potential 

Figure—Map showing the 13 Southern States covered by the Southern Research Station.

Foreword

Christie Staudhammer
vi • Wood to Energy: Using Southern Interface Fuels for Bioenergy

woody fuel users—including utility companies, industries, urban 

tree care industries, local forest landowners, local environmental 

organizations, and community leaders—need the resources and 

materials to advocate for implementing biomass fuel systems. This 

document seeks to remove a key barrier to using woody biomass 

for energy production by providing information that can help 

potential wood energy users prepare to bring this novel energy 

system to their communities. 

SCOPE AND SOURCES OF INFORMATION

This report focuses on biomass energy from woody materials 

in the WUI of the 13 Southern States and Puerto Rico. With a 

concentration on woody vegetation, we explicitly do not consider 

other important sources of bioenergy, such as corn-based ethanol 

and bagasse obtained from sugar cane. The target region of the 

report differs from other countries and other regions of the United 

States in many important ways, including climate, vegetation, 

topography, and demography. The target audience of the report 

includes resource professionals, the scientific community, and 

other technical professionals in related fields. Despite the report’s 

specific focus, many of its findings may be applicable to those 

people who are interested in other sources of bioenergy and who 

live in other regions.

Information sources for this document include scientific literature, 

governmental and nongovernmental reports and publications, 

and interviews with individuals, industry representatives, and 

citizens and leaders of communities considering bioenergy. 

More general materials can be found online in the Encyclopedia 

of Southern Bioenergy (forestencyclopedia.net/Encyclopedia/

bioenergy). Because technology advances rapidly, some 

unpublished data provided by experts in the field is reported and 

noted accordingly.

Foreword
Chapter 1

Wood to Energy: Using Southern Interface Fuels for Bioenergy 

Biomass has been defined as the total quantity of organic 

material in a given area at a particular time. Because biomass is 

so commonly available, there is a strong tradition of using it for 

energy in both the United States and abroad. Prior to the industrial 

revolution, biomass was used to supply almost all human energy 

needs, and woody biomass in particular was the source of over 

90 percent of the total U.S. energy consumption until 1850. In 

developing countries, biomass is still the dominant source of 

energy; billions of the world’s poor cook and heat with wood and 

other biomass, accounting for 14 percent of the world’s energy use 

(Sims 2002).

Today, biomass energy is derived from a variety of sources. 

Europeans take advantage of urban wood waste such as discarded 

pallets, right-of-way trimmings, and construction debris. In 

developing nations, rural poor derive biomass energy for heating 

and cooking from burning animal waste, or from timber cut 

specifically for this purpose. In the United States, sawmills burn 

woody residues for power, and some power generating plants 

have been designed to incorporate agricultural residues such as 

bagasse, orchard prunings, and nut hulls. 

Woody biomass could be an important source of energy in the 

Southern United States The South represents an important 

resource for the United States, producing more wood products 

than any other region of the country (Wear and Greis 2002). In 

particular, southern wildland-urban interface (WUI) areas, where 

human development is interspersed with undeveloped wildlands, 

represent a large forested land base containing a tremendous 

volume of available biomass. Woody biomass is available as 

a result of forestry activities such as thinning and harvesting. 

Increased frequency of natural disasters and conversion of forest 

land to urban land uses also provides a supply of woody biomass, 

as does the abundance of waste wood in the WUI. Moreover, 

potential users are geographically close to sources of biomass, so 

that the existing infrastructure network can be readily utilized.

BIOENERGY AND WOODY BIOMASS DEFINED

Bioenergy is renewable energy or heat produced from biomass. 

Biomass includes plant and animal material that can be used 

as an energy source or for chemical components, e.g., resins, 

fertilizers, and sugars. Manure, trees, crops, industrial byproducts 

and effluents, household waste, and forest residues are just a 

few examples of biomass. Biomass is also recently formed plant 

material, especially crops grown for their biomass that will be 

converted to useful energy (Smith 1983). Forest biomass includes 

accumulated above- and belowground mass, e.g., bark, leaves, 

and wood, derived from living and dead woody shrubs and trees. 

In this document, woody biomass includes tree boles, branches, 

tops, shrubs, hedges, twigs, and residues of wood processing. 

Worldwide, wood is the largest source of biomass for energy 

(National Atlas 2008), and it is the focus of this report. Because the 

South contains a large portion of readily available woody biomass, 

forests of the South could be a significant source of woody 

biomass for energy generation. The varied sources of woody 

biomass readily available in the WUI areas of the Southern United 

States are detailed in chapter 2. This includes forest residues from 

commercial harvests, nonmerchantable biomass from silvicultural 

activities, and urban wood waste; as well as woody biomass 

from land restoration and conversion and from short-rotation 

intensively managed forests.

Use of tops and branches from the merchantable harvest, 

nonmerchantable timber trees, and understory vegetation helps 

reduce fire hazard, increase stand productivity, and cut the cost 

of site preparation. After tree harvesting, woody biomass is 

commonly chopped, chipped, or pelletized in a preprocessing step 

and transported to conversion and power generation facilities. It 

is then converted into fuel, heat, or energy via thermochemical 

or biochemical processes, such as gasification, biogasification, 

or pyrolysis. Bioenergy is then produced through a variety of 

technologies, including steam or gas turbine cycles. Some 

conversion and power production technologies are more suitable 

for bioenergy from wood because of the fiber length, moisture 

content, and other physical and chemical properties of woody 

biomass. The harvesting and preprocessing of woody biomass 

for energy and fuels is covered in chapter 3 of this report, while 

chapter 4 discusses converting woody biomass to heat and energy. 

IMPORTANCE OF WOODY BIOMASS AS ENERGY

Worldwide, wood fuels account for 60 percent of total forest 

product consumption (Food and Agriculture Organization of 

the United Nations 2008); and in the United States, wood is a 

significant source of energy. This is especially true of the forest 

industry, which generates 56 percent of its own energy (American 

Forest and Paper Association 1996). 

Chapter 1

Introduction to Woody Biomass Energy

Christie Staudhammer
2 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Introduction to Woody Biomass Energy

While some wood is used in residential heating, most wood is 

used in larger scale power generation. Even in the most advanced 

mills, < 50 percent of a tree’s wood is made into lumber (Spelter 

and Alderman 2005). Thus, waste wood products, in the form 

of sawdust and wood chips, are a major byproduct of industrial 

sawmill operations, and often are burned to generate power in the 

wood products industry.

HISTORY OF ENERGY FROM BIOMASS FUELS

The self-sufficiency of the U.S. pulp and paper industries was 

initiated in the 1970s by energy crises that caused the industry’s 

internal energy production to increase dramatically; between 1972 

and 1986, the industry’s internal energy production rate nearly 

doubled to 57 percent (Zerbe 1988). 

Worldwide, there is a strong tradition of using biomass fuels in the 

same geographical region where the fuels are produced (Parikka 

2004). Because the Southern United States is a leading producer of 

forest products, residents of the region have been well positioned 

to take advantage of local biomass supplies. Beyond the forest 

products industry, small- and medium-scale bioenergy plants have 

been built to use these supplies and help other industries mitigate 

higher energy costs. The Russell Corporation, a textile company 

in Alabama and Georgia, was the first contemporary nonforest 

products company to install wood-fired boilers (Zerbe 1988). The 

Jack Daniel Distillery in Lynchburg, TN, installed two wood-coaloil-gas-fired boiler systems designed to use primarily green wood 

wastes from area sawmills and lumber yards. 

On a smaller scale, many homes, schools, and small institutions 

throughout the country use wood wastes to produce < 1 megawatt 

(MW) for space heating. A medium-sized educational institution 

in Mississippi uses wood to produce 10 MW of space heat; and 

schools and hospitals in Vermont, Montana, and Wisconsin use 

other small-scale bioenergy systems (LeVan-Green 2005). 

Across the country, agricultural and forest products residues are 

used in hundreds of heat and power plants, for a total of almost 

10 gigawatt (GW) of installed capacity (Sims 2003 1042 /id). These 

residues are in the form of branches, broken trees, leaves and 

needles discarded during harvest (forest residues), as well 

as sawdust, end cuts, and bark pieces generated during 

processing (primary process residues). According to Cook and 

Beyea (2000), about 1.7 exajoule (EJ) of energy are generated 

annually in the South, from biomass that includes nonwoody 

sources, but is primarily in fuelwood and residues from the forest 

products industries. 

Bioenergy development in the South and elsewhere, however, 

has not met its full potential. This shortfall led to the formation 

of bioenergy roundtables that brought together a range 

of stakeholders, including farmers, utility companies, and 

government agencies, with the goal of sharing concerns and 

engaging in fact finding, negotiating, and consensus building. 

The Southeast Bioenergy Roundtable has formulated two 

strategies: one is to focus on the use of biomass residues and the 

sustainable development of biomass crop potential to minimize 

environmental costs and maximize environmental benefits, and 

the other is to promote bioenergy market development (Cook and 

Beyea 2000). 

In a joint report, the U.S. Department of Energy and the U.S. 

Department of Agriculture reported that more than 1 billion 

dry tons of biomass is available each year for energy generation 

in the United States. This amount could replace 30 percent of 

U.S. petroleum consumption by 2030, a goal envisioned by 

the Biomass Research and Development Technical Advisory 

Committee (the committee was established by the Biomass 

Research and Development Act of 2000). Of the 1 billion dry 

tons available each year, 368 million dry tons come from 

nonmerchantable forest biomass resources. Depending on timber 

markets and energy prices, an additional 7.9 million dry tons are 

potentially available from commercial forest thinnings in the 

South (Perlack and others 2005). Chapter 5 of this report examines 

the supply of woody biomass in the WUI of the Southern United 

States, and chapter 6 presents an economic analysis of this supply. 

TRENDS IN POPULATION AND 

ENERGY USE IN THE SOUTH

Between 1990 and 2000, the population of the United States 

increased 13 percent, while the South’s population increased 

18 percent (U.S. Census Bureau 2000). The South now accounts 

for 34 percent of the total U.S. population. By 2020, the South’s 

population is expected to increase another 26 percent (Cordell 

and Macie 2002). This trend is driven by migration from other 

U.S. regions and from abroad. Over the period 1990 to 2000, net 

migration to the Southern United States was greater than to all 

other U.S. regions combined (U.S. Census Bureau 2000).

As the population of the United States has grown, so has the 

country’s energy consumption. From 1985 to 2005, energy 

consumption in the United States grew by an average of 2 percent 

per year; moreover, while the United States accounts for < 5 

percent of the world’s population, it consumes about 22 percent of 

the world’s energy (Energy Information Administration 2008).

From 1994 to 2004, per capita energy consumption in the United 

States increased from 215 to 340 million British thermal units 

(Energy Information Administration 2005). In the Southeast in 

particular, electricity demand represents a relatively larger share 

of total U.S. electricity sales, and the Southeast’s need for new 

electricity capacity is greater than in other regions of the country 

(Energy Information Administration 2006). Residential-delivered 

energy use is projected to increase by 9 percent between 2003 

and 2010, up 23 percent by 2025, with 68 percent of this growth 

expected to come from increased use of electricity. Projected 

housing growth in the South, where almost all new homes will 

use central air conditioning, is an important component of the 
Wood to Energy: Using Southern Interface Fuels for Bioenergy • 3

Chapter 1

projection, as is increased use of consumer electronics across the 

country (Energy Information Administration 2005). In the southern 

WUI, bioenergy can help meet this projected increase in demand 

for energy.

TRENDS IN LAND USE CHANGE IN THE 

WILDLAND-URBAN INTERFACE

The median age of residents in the South and elsewhere is rising, and 

by 2020, more than 17 percent of people in the region will be over 

65. While the population growth is occurring mostly in urban areas, 

driving new development and expansion of the WUI, rural areas are 

also expected to grow by 12 percent (Cordell and Macie 2002). 

Meanwhile, the trend in the 1990s toward large-scale conversion 

from rural to urban development indicates that new rural residents 

can contribute substantially to the expansion of WUI areas. Most of 

the rural South’s private landowners maintain a strong conservation 

ethic, but as these landowners get older, they are selling their land, a 

recent trend that makes predictions from historical patterns difficult. 

Nevertheless, population growth is expected in many counties that 

are heavily forested, which will create pressure for development 

as well as timber harvesting. Additionally, as urbanization and 

population expands into rural areas, there will be additional 

pressures on lands for recreation and wildlife habitat. In interface 

communities, jobs in forestry, mining, and fisheries have been stable 

and are projected to remain so (Cordell and Macie 2002). However, 

farming has employed ever smaller proportions of the South’s 

workforce, a trend that is expected to continue its decline. Jobs are 

projected to shift from farming and manufacturing to service, retail, 

technology, and other urban industries, a change that will result 

in higher wages on average. In turn, higher average wages likely 

will cause further housing development in the WUI and increased 

energy demands.

STRATEGIES IN U.S. ENERGY POLICY

Over the last decade, proposed energy strategies for the United 

States have included increasing energy efficiency, storing carbon 

in forests and other ecosystems, and displacing fossil fuels with 

energy sources that are CO2

 neutral (Cook and Beyea 2000). CO2-

neutral energy sources are balanced with respect to how much 

carbon is produced in their making versus how much carbon is 

released in their use, i.e., no net carbon emissions result from CO2

-

neutral energy sources. 

In recognition of the potential socioeconomic and environmental 

benefits from bioenergy generation, the Farm Bill 2002, Title IX, 

provides loan guarantees and grants to farmers, ranchers, and 

small business owners who support renewable energy projects 

in rural areas. Other sections of Title IX provide for Federal 

procurement of biobased products, biomass research and 

development, and continuation of the bioenergy program. 

Similarly, the Energy Policy Act of 2005 provides for grants, credits, 

loan guarantees, incentive payments, and Federal mandates 

relevant to the production of biopower and biofuels, including 

grants to improve commercialization of forest biomass for 

electricity generation and other energy conversion processes. The 

Policy Act also amends the Biomass Research and Development 

Act of 2000 by adding provisions for regional bioeconomy 

development grants. 

Climate change legislation supports bioenergy development, with 

the Sense of the Senate on Climate Change Resolution (passed 

June 22, 2005) bringing greater attention to environmental 

problems that bioenergy can mitigate (Smith 2005). The 2007 

Farm Bill confirmed this support, improving and increasing 

funding for the bioenergy program and creating a biomass 

energy reserve program to develop new feedstocks for renewable 

energies, such as cellulosic ethanol. Moreover, Title VIII of the bill 

established a Forest Bioenergy Research Program, providing $75 

million to address issues related to woody biomass for bioenergy 

production (U.S. House of Representatives 2008).

While increased energy efficiency is a long-term strategy, 

there is also public pressure to address other ecological and 

social challenges, including air quality in urban and rural areas, 

ecological integrity and biodiversity on cropland and forests, 

trade deficit and national security costs of petroleum, and markets 

for wood waste and less desirable wood (Cook and Beyea 2000). 

Chapter 7 discusses public perceptions of biomass and new 

interest in bioenergy as it pertains to community environmental 

and economic sustainability. 

SOCIAL, ECONOMIC, AND ENVIRONMENTAL 

BENEFITS OF BIOENERGY

Potential social, economic, and environmental benefits of 

bioenergy are widely recognized. The major environmental 

benefit of bioenergy is the reduction of greenhouse gas emissions. 

When fossil fuels are displaced by sustainably produced biomass 

fuels, CO2

 released in power generation is mitigated by carbon 

resequestered from the atmosphere as biomass stocks regrow. 

Greenhouse gas emissions are also reduced by increasing 

the amount of carbon stored onsite, e.g., by reforestation of 

agricultural lands or mined lands. During photosynthesis, 

trees absorb CO2

 and break it down into oxygen and carbon. 

Oxygen is released back into the atmosphere, and the carbon 

is stored (sequestered) in the tree stem, branches, and roots. 

Thus, if treeless landscapes are replaced by forested land, there 

will be a net carbon accumulation on these sites. Reforestation 

and afforestation can also create other environmental benefits, 

including better soil and water quality, as well as improved wildlife 

habitat that consists of greater biological and structural diversity.

Localized environmental problems, such as nitrogen oxide (NOx

), 

sulfur oxide (SOx

), and mercury emissions, can also be mitigated 

through reduced fossil fuel combustion, because bioenergy 

production systems release far lower levels of these compounds 
4 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Introduction to Woody Biomass Energy

into the atmosphere (Marland and others 2000; Sims 2002, 

2003). Creating markets for woody biomass can offset costs of 

thinning overgrown or diseased forest stands, measures that 

can improve forest health and reduce forest fuel loads and fire 

risk in the WUI. Planting and maintaining forests can also help 

control encroachment of fire-intolerant or invasive trees, restore 

native ecosystems, and make forested land more economically 

competitive through alternative land uses, all of which maintains 

green space in developing areas. 

Short-rotation woody crops (SRWC) used as dedicated energy fuel 

supply systems can reduce nutrient loading from reclaimed waste 

water and other urban and rural wastes, restore mined lands, and 

control invasive exotics such as cogongrass (Imperata cylindrica)

(Rockwood and others 2004). Furthermore, SRWC systems 

typically sequester more carbon, require less fertilization and 

energy inputs, cause less soil erosion, and have higher biodiversity 

values than conventional agricultural systems (Tobert and Wright 

1998, Tobert and others 2000). Socioeconomic benefits from 

bioenergy include not only energy security through reduced 

dependence on imported oil but also generation of employment 

and resulting economic multiplier effects in rural communities. 

POTENTIAL NEGATIVE CONSEQUENCES OF 

BIOMASS ENERGY PRODUCTION IN THE 

WILDLAND-URBAN INTERFACE

Potential negative consequences from biomass energy production 

in the WUI include losses of natural areas, e.g., temporary loss 

from harvest and planting of SRWC, air pollution, soil nutrient 

depletion, and potentially higher costs for energy. The impacts of 

biomass energy production on the environment are comparable 

to those of conventional forestry practices in WUI areas, and less 

than those associated with agricultural land uses; moreover, 

appropriate management practices can mitigate the impacts.

Obtaining woody biomass from waste sources of wood is 

inexpensive and does not affect standing plantations and natural 

areas. However, using wood obtained from conventional logging 

practices has a direct impact on the forest environment, such 

as wildlife habitat loss and soil compaction, and some biomass 

generating activities, e.g., precommercial thinning, may be 

expensive (Koning and Skog 1987). As harvesting specifically 

for woody biomass becomes more commonplace, advances in 

technology likely will mitigate costs (Zerbe 1988). In some parts 

of the United States and elsewhere, overthinning young, high 

quality trees could lead to a loss of future high value timber (Koning 

and Skog 1987). However, in the South, due to a large number 

of overstocked stands, thinning is a common and beneficial 

silvicultural treatment that promotes higher quality timber growth 

and guards against southern pine beetle outbreaks (Florida 

Department of Agriculture & Consumer Services 2008). 

A more substantive concern is that removal of thinned material 

might result in the loss of valuable nutrients in the woody 

materials that are removed from the site (Parikka 2004). However, 

fertilization and other silvicultural practices can alleviate the loss. 

Another concern is that biomass energy production might result 

in the conversion of natural areas to plantations, leading to 

reduced biodiversity from an impaired ecosystem function (Cook 

and Beyea 2000), or increased disturbance from higher impact 

or reentry logging practices (Fung and others 2002). Silvicultural 

practices favor faster growing species or lead to increased fertilizer 

and pesticide use could reduce biodiversity (Fung and others 

2002) and negatively impact wildlife and recreation (Koning and 

Skog 1987). Some researchers, e.g., Patzek and Pimentel 2005, 

have warned of potential degradation of soil nutrients, structure, 

and diversity in industrial biomass production. These concerns, 

however, are comparable to those of conventional forestry. 

Moreover, if land conversion takes place in agricultural areas in 

the WUI, these pressures will be mitigated by promoting land use 

more consistent with historical natural patterns.

Air pollution concerns arise from the harvest, transportation, 

and energy conversion of woody biomass. Indirect emissions 

come from energy carriers during transportation and extraction 

(Wahlund and Westermark 2004). During combustion, particulatederived pollution produced with wood can be high because of 

the still prevalent use of obsolete conversion technologies, e.g., 

residential homes with conventional wood-burning fireplaces, 

and because of poorly developed emissions controls (Zerbe 1988). 

Furthermore, wood waste from building sites and demolition 

may contain preservative treated and painted wood, which could 

result in the release of toxic residues if materials are not sorted 

prior to combustion. 

The biggest barrier to biomass energy adoption is not technical 

but rather economic (Hoffmann and Weih 2005). High costs 

are associated with harvesting, collecting, and especially 

transporting biomass fuels (Wahlund and Westermark 2004, Zerbe 

1988). Moreover, there is a lack of infrastructure for marketing 

biomass fuel products, and with some notable exceptions in 

some geographic areas, there is no viable market for young, 

thinned material. Market development will not take place until 

biomass suppliers have a guarantee that they will have buyers 

over the long term, and utility companies will not invest in 

biomass conversion technologies unless they have a guaranteed 

economically viable supply of biomass. The impasse means that 

both the utility industry and forest products industry are reluctant 

to make capital investments without long-term contracts (Zerbe 

1988). Utilizing fuel wood from the WUI and locating conversion 

and power facilities nearby, however, will mitigate most of 

these costs, and forested WUI communities that have leaders 

knowledgeable about their woody biomass supply are well poised 

to make appropriate long-term commitments. 

A further change in energy policy could help make these capital 

investments occur. The U.S. Government continues to subsidize 
Wood to Energy: Using Southern Interface Fuels for Bioenergy • 5

Chapter 1

coal, oil, natural gas, and nuclear power. Federal subsidies for 

primary energy in year 2007 were estimated at $11.2 billion 

(Energy Information Administration 2007). Other countries, 

including Sweden and Norway, have introduced carbon tax 

policies that partly level the playing field among energy 

technologies (Fischer and Newell 2004, Hoffmann and Weih 

2005). Sweden has made biomass attractive through government 

subsidies for short-rotation plantations, higher taxes on fossil 

fuels, and the creation of a biofuel market. 

CONCLUSIONS

Woody biomass is a viable alternative to conventional fossil fuels, 

and fits well with proposed U.S. energy strategies to promote 

carbon-neutral energy sources. As the South’s population and 

energy demands increase, the region is well positioned to take 

advantage of woody biomass sources. The South is home to a 

large and long-established forest products industry that produces 

an abundant supply of woody biomass materials, especially true in 

expanding interface areas subject to land conversion pressures. 

Careful planning can mitigate most negative consequences of 

obtaining and using woody biomass. Some issues, such as high 

transportation costs, are substantially of less concern in the 

WUI where bioenergy plants and woody biomass sources are 

often close geographically. Moreover, where forestry practices 

replace traditional agriculture, most negative consequences 

all but disappear. The positive externalities associated with 

woody biomass include benefits to the soil, water, atmosphere, 

environment, and community. Forests filter impurities, providing 

clean water, and continuous forest cover helps control erosion. 

Using woody biomass will have positive environmental impacts 

through reduced NOx

 and SOx emissions and increased carbon 

sequestration. Moreover, afforestation and reforestation will 

promote habitat restoration and biodiversity. Finally, bioenergy 

projects using woody biomass will create positive local and 

regional economic impacts for WUI communities and rural areas. 

Using woody biomass as an alternative energy source can help 

preserve natural areas and reduce reliance on fossil fuels. 

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6 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

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of Agriculture Forest Service, Forest Products Laboratory. 85 p.

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belowground carbon sequestration with conversion of agricultural lands 

to production of bio-energy crops. New Zealand Journal of Forestry 

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Legislation/110/FB/Forestry%20Title.pdf. [Date accessed: March 3].

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Research and Public Policy. Winter: 38–47.
Wood to Energy: Using Southern Interface Fuels for Bioenergy • 7

Chapter 1

bioenergy: heat and/or electricity produced from biomass energy 

systems, usually measured in J (J of energy per gram of fuel), 

MJ/g, or GJ/g.

biofuels: liquid fuels made from biomass, which are used for 

transportation or cooling.

biogas: a gas that is produced from biomass that is usually 

combustible.

biomass: plant and animal material that can be used as an energy 

source or for chemical components; e.g., trees, crops, algae and 

other plants, agricultural and forest residues, organic industrial 

byproducts and household waste, food manufacturing effluents, 

sludges, and manures.

Btu: British thermal unit. A standard unit of energy that is the 

amount of energy equal to the heat required to increase the 

temperature of 1 pound of water 1 degree Fahrenheit.

cofiring: introducing biomass as a supplemental energy source in 

coal plants.

cogeneration: the simultaneous production of heat and 

electricity from a single fuel, also called combined heat and 

power.

comminution: reduction of woody biomass to wood chips, e.g., 

by hammermill or chipper.

forest biomass: the accumulated above- and belowground mass, 

including bark, leaves, and wood, from living and dead woody 

shrubs and trees.

forest residues: the aboveground materials generated from 

logging during precommercial thinnings and harvesting 

operations, e.g., leaves, bark, tops, and broken trees. 

fuel preprocessing: techniques for producing upgraded biomass 

fuel, such as drying and densification, which can lead to more 

homogenous, higher energy content fuels.

gross primary production: total amount of organic matter 

produced as trees convert carbon dioxide and water to solar 

energy through photosynthesis.

hog fuel: biomass generated by grinding wood and wood waste 

for use in a combustor.

industrial forestry process residues: residues that result from 

the incomplete use of wood raw material.

joule (J): a unit of electrical energy; 1 MJ is the amount of energy 

needed to raise a 1 mt object to a height of 100 m. (On average, 

54,000 MJ of energy are needed to heat a single family house for 

1 year under continental climate conditions.)

kilowatt: rate of electrical power output.

logging residues: poor quality trees and tree components, such 

as crowns and stump-root systems that are left onsite during 

commercial harvesting operations. 

net biomass increment: change in accumulated biomass over a 

measurement period. 

net primary production: the photosynthates that are not 

consumed during respiration, but are incorporated into the 

various tree components during the assimilation process.

precommercial thinning: a silvicultural treatment or type of cut 

in which young trees are removed to promote growth of the 

remaining trees.

primary process residues: residues that result from primary 

wood processing, e.g., lumber, veneer, pulp, and paper, such as 

bark, sawdust, cores, slabs, and black liquor.

pyrolysis: the process of combusting during oxygen-starved 

conditions, which involves the physical and chemical 

decomposition of solid organic matter by heating into liquid, 

gas, and carbon char residue.

secondary process residues: residues that result from secondary 

wood processing, e.g., furniture manufacturing, such as sawdust 

and small scrap wood.

short-rotation crops: crops, such as rapeseed, grown and 

harvested for biomass production over a short time frame.

short-rotation forests: trees, such as eucalypts, grown and 

harvested for biomass production over a short time frame, 

usually 5 years or less.

short-rotation woody crops (SRWC): a silvicultural system 

based upon short clear-felling cycles, generally between 1 

and 15 years, employing intensive cultural techniques such 

as fertilization, irrigation and weed control, and utilizing 

genetically superior planting material (Drew and Mitchell 1987). 

silvicultural residues: trees smaller than merchantable size that 

are left intact at the site of precommercial thinnings.

wildland-urban interface (WUI): areas where increased human 

influence and land use conversion are changing natural 

resource goods, services, and management (Hermansen and 

Macie 2002). 

wood residues: the waste materials generated from wood 

processing operations, e.g., bark, wood chips, sawdust, and 

broken lumber.

Glossary of Terms

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 9

Chapter 2

INTRODUCTION

The wildland-urban interface (WUI) in the Southern United 

States contains a variety of woody biomass sources that could be 

used for bioenergy. The WUI is defined as the area where human 

development is interspersed with undeveloped wildlands. In 

the South, these wildlands are fragmented by commercial and 

residential development and composed primarily of private 

forest lands. 

Southern forest lands represent an important resource for the 

United States, producing more wood products than any other 

region in the Nation (Wear and Greis 2002). The nature and 

trends of land ownership and use in the South influence the 

availability of woody biomass. Conversion of agricultural land 

to forest land has increased the annual yield of forest products, 

while clearing of forested lands for urban use has produced 

one-time harvests of available woody biomass. Concurrently, a 

slowing pulpwood market has depressed stumpage prices for 

small-diameter trees, leaving many forests overstocked due to 

the increased cost of thinning and increasing the availability of 

low-cost woody biomass. 

Woody biomass users in the South can also benefit from having 

various sources of residue, including timber harvests, thinnings 

of plantations and natural stands, urban wood residue from 

yard trimmings, commercial tree care industry and utility line 

clearings, municipal solid waste, invasive plant removal, native 

plant restoration, and phytoremediation projects. Because 

the South contains a large portion of readily available woody 

biomass, the working forests of the South could be a significant 

source of woody biomass for energy generation. This chapter 

reviews the varieties of woody biomass that can be found in the 

WUI of the South. 

FOREST RESOURCES IN THE 

WILDLAND-URBAN INTERFACE

Forest resources in the WUI consist of three primary components: 

(1) merchantable standing timber, (2) forest residues from 

commercial harvests, and (3) nonmerchantable timber removals. 

Since merchantable timber has higher value alternative markets, 

woody biomass resources for energy are likely to be limited to the 

remaining nonmerchantable components, which include trees 

that have not attained sufficient size, are of poor quality, or are 

nonmerchantable species, as well as residue material produced in 

the course of forestry activities. 

These materials, including forest residues as well as the products 

of precommercial thinnings and fuel mitigation harvests, are the 

primary source of forest residue biomass (Perlack and others 2005). 

Forest residues from commercial harvests and nonmerchantable 

timber removals are often grouped with mill residues such as 

sawdust and bark to form what is known as “total forest residues.” 

In this context, “nonmerchantable biomass resources” refers to 

resources that have no conventional timber forest product market, 

although, if bioenergy markets are developed, nonmerchantable 

forest and urban residues could have commercial value. However, 

for the foreseeable future, it is likely that energy wood will be the 

lowest valued wood product harvested from the forest.

THE SOUTHERN FOREST RESOURCE

The amount of woody biomass available for energy in the 

Southern United States is strongly linked to the amount of forest 

land and the level of forest operations undertaken in the region. 

The Forest Service defines forest land as “land at least 10 percent 

stocked by forest trees of any size, including land that formerly 

had such tree cover and that will be naturally or artificially 

regenerated.” Timber lands are defined as “forest land that is 

producing or is capable of producing crops of industrial wood,” 

while reserved lands are those that have been “withdrawn from 

timber utilization by statute or administrative regulation” (Smith 

and others 2004). The South makes up 24 percent of the total area 

of the United States but 40 percent of U.S. timberland (totaling 

203 million acres, or 82 million ha), making the South the largest 

timberland region in the United States (fig. 2.1). With its large 

Chapter 2

Woody Biomass Sources in the Wildland-Urban Interface

Christie Staudhammer, Richard Schroeder, Brian Becker, and Matthew Langholtz

0

100

200

300

400

500

600

700

800

North South Rocky

Mountain

Pacific

coast

Region

Area (million acres)

Timberland

Other forest land

Reserved forest land

Nonforest land

Figure 2.1—Area of major forest land types by U.S. Department of 

Agriculture Forest Service region (adapted from Smith and others 2004).
Woody Biomass Sources in the Wildland-Urban Interface

10 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

timberland area and long growing season, the South contributed 

63 percent of the U.S. timber harvest in 2001, up from 51 percent 

in 1986 (Smith and others 2004). Land class details for the South 

by State are shown in table 2.1.

In 2003, 5 million private landowners owned 89 percent of the 

South’s 215 million forest acres. As shown in figure 2.2, in 1999, 

69 percent (138 million) of the 203 million acres of timberland 

in the South was nonindustrial private forest and 20 percent (40 

million) was owned by forest industry (Wear and Greis 2002). 

Plantations were approximately 19 percent (35 million acres) 

private forests and 8 percent (2 million acres) public forests (Smith 

and others 2004). 

Timberland acreages in the South have been fairly stable since 

the 1950s, but the South’s privately owned forests have been in 

flux and are influenced by various social and economic factors. 

For example, gains in forest area from abandoned agricultural 

lands have been offset by conversion of southern forests to urban 

development (Wear and Greis 2002). Pine plantations in the 

South are projected to increase to 54 million acres by 2040, 

a 60-percent increase from 1995 (Wear and Greis 2002). Pine 

plantations in southern private forests are projected to increase 

14 million acres by 2050, associated with a 15- and 18-percent 

decline in natural pine and upland hardwood forests, respectively 

(Alig and others 2002). 

Trends in timber prices are indicative of the relative scarcity 

of forest products and can indicate the strength of the forest 

industry in the South. Between 1988 and 1998, prices of hardwood 

pulpwood, softwood pulpwood, and softwood sawtimber 

increased at rates of 12, 5, and 8 percent, respectively. Hardwood 

sawtimber prices increased 6 percent between 1992 and 1998, 

reflecting a scarcity of timber products during that period. 

However, since 1998, the southern timber markets have been 

in a period of transition. In 2005, southern softwood pulpwood 

Table 2.1—Land area in the South by major class and State, 2002

 

Land class

Forest land

State 

Total land 

areaa

Total forest 

landb Timberland Reserved Other 

Other 

land

thousand acres

Alabama 32,481 22,987 22,922 65 0 9,494

Arkansas 33,328 18,771 18,373 231 167 14,557

Florida 34,520 16,285 14,636 1,121 528 18,235

Georgia 37,067 24,404 23,802 595 7 12,663

Kentucky 25,428 12,684 12,347 305 32 12,744

Louisiana 27,883 13,812 13,722 90 0 14,071

Mississippi 30,025 18,580 18,572 8 0 11,445

Oklahoma 43,955 7,665 6,234 45 1,386 36,290

North Carolina 31,180 19,302 18,664 598 40 11,878

South Carolina 19,272 12,495 12,301 194 0 6,777

Tennessee 26,381 14,396 13,956 440 0 11,985

Texas 167,626 17,149 11,774 125 5,250 150,477

Virginia 25,342 16,073 15,371 686 16 9,269

South total 534,488 214,603 202,674 4,503 7,426 319,885

a Total land area is comprised of Total forest land and Other land.

b Total forest land is comprised of Timberland, Reserved, and Other. 

Source: Smith and others (2004). 

Other public

forests

 5% 

Nonindustrial

private forests

69% 

Industrial

forests

20%

National forests

6%

Figure 2.2—Distribution of 203 million acres of Southern U.S. timberland 

in 1999 (Wear and Greis 2002).
Chapter 2

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 11

prices fell to their lowest since 1997 (Wear and others 2005); and 

southern pulpwood production declined from 181 in 1994 to 162 

million green tons in 2003 (Johnson and Steppleton 2005). Since 

1998, prices for other timber products have leveled or declined. 

The market decline has been attributed to a combination of 

technological change, product substitution, pulpmill capacity 

decline, increased imports, use of recycled materials, and some 

loss of competitive advantage to mills in Latin America (Wear and 

others 2005). In spite of the timber market contraction since 1998, 

demand for forest products is projected to continue as domestic 

and international populations increase, and softwood inventories 

in the South are projected to exceed current growing stock through 

2040, with hardwood inventories peaking in 2025 (Adams and 

others 2003, Wear and Greis 2002). Small-diameter timber currently 

sold for pulpwood could be an economically viable resource for 

energy under conditions of low wood prices and high energy costs.

FOREST RESIDUES FROM COMMERCIAL HARVEST

Perlack and others (2005) estimated that 368 million dry tons per 

year of sustainably available biomass could be obtained from 

forest lands nationwide, primarily from forest residues, silvicultural 

treatments, and fuelwood extractions. The amount is more than 

twice what is currently used for bioenergy from both agriculture 

and forestry resources. Estimates based on the Timber Product 

Output (TPO) Database Retrieval System (U.S. Department of 

Agriculture Forest Service 2005) indicate that 49 million dry tons 

of logging residue could be obtained annually nationwide. In the 

South, 17.5 million dry tons of logging residue was produced in 

2002. Though not all logging residue can or should be harvested 

for biofuels, even a small percentage of this total represents a 

significant resource. Removals and forest residues by hardwood 

and softwood class for each Southern State are shown in 

figure 2.3.

Forest residues consist of four major components: (1) tops, (2) 

limbs, (3) stumps, (4) and unutilized cull trees. In a recent study 

in east Texas, 17.6 percent of the total logging residue was 

stumps, with the remainder in tops, limbs, and culls (Xu and 

Carraway 2005). While roots and stumps can be a significant 

part of plantation biomass, the cost associated with recovery is 

high, the wood is often contaminated with soil, and ecological 

studies suggest that removal might not be desirable (Hakkila and 

Parikka 2002). Tops, branches, and small stems, often referred 

to as logging slash, present harvesting and handling challenges 

because this material is generally less than one-fourth the 

density of solid wood, which increases the harvesting cost per 

ton (Rummer and others 2004). Moreover, skidding logs from the 

stump site to the landing tends to leave the tops contaminated 

with soil and stones. Soil contamination results in high levels of 

ash when biomass is combusted, leading to slagging and fouling 

which can cause damage to furnaces and boilers (Sims and 

Bassam 2003). 

In conventional forestry, forest residues not directly utilized are 

left in the forest to degrade naturally for the recycling of nutrients, 

discarded in piles or windrowed for wildlife habitat, or burned on 

site for disposal. Burning in a boiler for bioenergy would reduce 

the pollution associated with open burning and the release of 

methane (a greenhouse gas) caused by material decomposition. 

Forest residues utilized for bioenergy usually go straight from 

the forest to a chip pile with 40 to 50 percent moisture and are 

burned “as is.” Field drying of forest residues can reduce the 

moisture content and grinding will increase the density, reducing 

the haul cost per British thermal unit (Btu), which results in more 

cost-effective handling. However, allowing material to air-dry in 

the field for several weeks will increase travel costs, as multiple 

trips to the harvest site would be required. Estimates of available 

forest residues can be found in the Forest Service, Southern Forest 

HW SW HW SW HW SW HW SW HW SW HW SW HW SW HW SW HW SW HW SW HW SW HW SW HW SW

AL AR FL GA KY LA MS NC OK SC TN TX VA

Billion cubic feet

1,400

1,200

1,000

800

600

400

200

0

Roundwood product Other removals Logging residues

Figure 2.3—Volume (bcf ) of roundwood product, other removals, and logging residues for hardwoods (HW) and softwoods (SW), 2002.
Woody Biomass Sources in the Wildland-Urban Interface

12 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Resource Assessment (U.S. Department of Agriculture Forest 

Service 2004).

NONMERCHANTABLE BIOMASS FROM 

SILVICULTURAL ACTIVITIES

Most of the nonmerchantable biomass resource in the South is 

associated with conventional forestry operations, which usually 

include silvicultural activities, such as precommercial thinning 

to improve the quality of future harvests, and preventative 

treatments, such as insect or fuel reduction harvests. In the 

Southern United States, many silvicultural activities are driven by 

concerns about overstocked forests (Wolfe 2000), especially in the 

WUI where traditional forestry activities are often restricted. 

Forests with an overabundance of small-diameter trees 

require thinning because the forests are at increased risk for 

insect outbreaks, such as the southern pine beetle. Moreover, 

overstocked forests have a higher risk of fire, and as WUI 

populations increase, the threat to residential and commercial 

structures from wildfire in forests within and adjacent to the 

WUI increases. Public concern over smoke and out-of-control 

fires raises questions about controlled burning as a fuelmitigation strategy (Shindler and Toman 2003). This has led 

some communities to explore fuel mitigation harvesting for 

bioenergy (Farnsworth and others 2003). Perlack and others 

(2005) estimated that material from thinnings in the South could 

produce 8 million dry tons annually, at a low cost.

For either silvicultural thinning or insect and fire mitigation, the 

available woody biomass is smaller in diameter than commercial 

forest harvest. A study in the Western States found that most stems 

that were to be removed by fuel reduction treatments were < 2 

inches in diameter. Eighty-six percent of the trees were < 10 inches 

in diameter, although they only accounted for 28 percent of the 

total volume (U.S. Department of Agriculture Forest Service 2003). 

Forest resources within the WUI represent significant volumes. 

For example, Ku and Baker (1993) determined that in southern 

Arkansas and northern Louisiana the volume of biomass < 5.5 

inches in diameter averaged 10.5 dry tons per acre, with no 

difference between winter and summer harvest. In their analysis, 

high density pine stands produced 53 percent more biomass than 

high density pine-hardwood stands. 

On the other hand, economic feasibility is an issue. A 1992 study 

reported that only 40 percent of the hardwood inventory in 

Tennessee was economically available (Perlack and others 2005). 

However, if biomass is harvested and processed using integrated 

systems for merchantable products and biomass, economical 

recovery can be > 90 percent.

URBAN WOOD WASTE 

As the U.S. landscape evolves, the amount of forest land within 

the WUI increases. However, traditional forestry practices may not 

be widely accepted in these areas because average tract sizes are 

small and harvesting results in close contact with neighboring 

residents. If neighbors object to certain harvesting techniques or 

prescribed burning, different management approaches to land 

management and woody biomass collection will be required. In 

addition to forest plantations within the WUI, woody biomass is 

also generated from tree and yard trimmings, commercial tree 

care industry, utility line clearings, and green space maintenance. 

Some of this material enters the solid waste stream, while other 

portions are handled by the generator or at its origin.

Urban wood waste is a significant woody biomass resource. One 

study estimated the annual volume of woody yard trimmings 

in the United States at 9.8 million dry tons annually, based 

upon an average moisture content of 40 percent (Perlack and 

others 2005). Another study on urban wood waste from 30 U.S. 

metropolitan areas determined that municipal solid waste (MSW) 

wood, industrial wood, and construction/demolition (C/D) debris 

averaged 666 pounds per person per year. Several southern cities 

were included in the study, and generation rates in the Southern 

United States varied from a low of 494 pounds per person per 

year (Florence, SC) to a high of 1,504 pounds per person per year 

(Richmond, VA) (Wiltsee 1998).

The U.S. Environmental Protection Agency reported that 28.6 

million tons of yard trimmings (vegetative material that enters the 

solid waste stream from residential, commercial, and institutional 

sources, excluding C/D debris) were generated in the United 

States in 2003, representing 12 percent of the total U.S. MSW 

and equating to an average of about 190 pounds of trimmings 

per person per year (based on 2003 population figures) (U.S. 

Environmental Protection Agency 2005). 

The amount of yard trimmings generated within each community 

varies significantly. Using 2000 population figures and State MSW 

data, Florida’s yard trimmings were 14 percent of its total MSW and 

averaged 452 pounds per person per year. In contrast, Virginia’s 

yard trimmings were only 4 percent of its total MSW, amounting to 

about 221 pounds per person per year (Commonwealth of Virginia 

2002, Florida Department of Environmental Protection 2003, U.S. 

Census Bureau 2005). Nationally, in 2003 about 56 percent of yard 

trimmings were recycled, most of which was composted (U.S. 

Environmental Protection Agency 2005).

Yard trimmings consist of tree trimmings, grass clippings, garden 

wastes, prunings, leaves, Christmas trees, and the wood waste and 

paper component of domestic garbage (Sims 2002). The material 

from residential curbside and commercial landscaping sources 
Chapter 2

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 13

often is dominated by smaller, higher moisture material. A study 

of curbside-collected yard trimmings in Florida found that most 

of the material (by weight) was grass clippings (fig. 2.4A) (Florida 

Organics Recyclers Association 1996). 

Grass clippings and smaller trimmings from shrubs generally 

have higher moisture content (often > 50 percent) and levels 

of soil contamination than do larger diameter woody material. 

However, grass and leaves also contain higher levels of degradable 

carbohydrates and are more suitable for composting or other 

biodegradation. People tend to bring more woody material to 

central dropoff locations instead of leaving them curbside (fig. 

2.4B) (Florida Organic Recyclers Association 1996). Material of 

this type has been found to have a moisture content of about 

45 percent and fairly low levels of soil contamination (Atkins 

and Donovan 1992) as compared to curbside-collected material. 

However, larger material was also more likely to have large pieces 

of contamination such as scrap metal, rock, or concrete, and these 

contaminants present processing difficulties. 

In addition to yard trimmings, trees and tree debris are generated 

by line clearing, right-of-way maintenance, and green space 

maintenance by utility companies and local governments. This 

material contributes to the biomass harvest from the urban 

forest but sometimes does not enter the MSW stream. A 1994 

study found that an estimated 56,000 arboriculture and urban 

forest industry firms exist in the United States (NEOS 1994). These 

municipal and commercial tree care firms generated an estimated 

200 million cubic yards of material (fig. 2.5A), with residues 

distributed similarly to those of Florida, which are displayed in 

figure 2.4A. Residues generated by these firms are often difficult 

to dispose of, and survey results showed that 42 percent of this 

material was given away (fig. 2.5B). 

Many State legislatures have banned the disposal of tree and 

landscape residue in landfills, increasing the cost of disposal. 

The high cost of disposal (tipping fees) at most MSW landfills has 

forced many commercial tree companies to seek alternatives for 

handling the woody biomass generated in their operations. In 

some locations, logs are occasionally removed from the urban 

wood stream and marketed to wood products manufacturers, 

as some tree species yield economic returns of two to four times 

more in lumber than firewood (Cesa and others 1994). However, 

metal in logs, e.g., from wires and nails, reduces sawmill demand 

for these logs. 

Natural disasters also generate considerable woody debris. 

Seventy-eight percent of natural disaster woody material comes 

from wind storms, and 16 percent from ice storms or freezes. 

Of the material generated from natural disasters, 97 percent of 

the volume is generated in municipal areas with populations 

> 100,000. Seasonally, about 58 percent of the volume was 

produced in the summer and fall, and about 42 percent in the 

winter and spring (NEOS Corp. 1994).

In addition to the material generated by the urban forest industry, 

some urban wood waste ends up classified as C/D debris because 

site conversion and land clearing often is accompanied by new 

construction. C/D debris can vary from as low as 15 to as high 

as 85 percent wood, depending upon the source of the waste 

and where in the solid waste stream the wood is measured 

(Atkins and Donovan 1992). However, C/D debris is also often 

Logs and tree

cuttings

10% 

Small veg.

debris

9%

Nonveg.

material

3% Leaves

0%

Grass

38%

Brush and shrub

28%

Palm

fronds

12%

Grass

clippings

4%

Small veg. 

debris

3% Nonveg.

material

1%

Woody

material < 1"

54%

Woody

material > 1"

28%

Palm fronds

10%

(A) (B)

Figure 2.4—Percent of total weight of curbside-collected yard trimmings (A), and yard material brought to central dropoff locations in Florida (B) (adapted 

from Florida Organic Recyclers Association 1996).
Woody Biomass Sources in the Wildland-Urban Interface

14 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

contaminated with paint, preservatives, and other substances 

that may be harmful to the environment if burned or otherwise 

used directly for bioenergy. These materials may require special 

processing to ensure that additional pollution does not result 

from their use as fuel.

EXOTIC PLANT REMOVALS, NATIVE PLANT 

RESTORATION, AND LAND CONVERSION

Exotic plant eradication programs are another recurring source of 

biomass for bioenergy. Issues related to invasive plant species are 

increasing in the WUI as human influences and human-induced 

disturbances increase. Harvesting for fuelwood can also be 

integrated into restoring degraded or high-graded lands or for 

native plant restoration projects (Andersson and others 2002). In 

the Southern United States, bioenergy markets could facilitate 

ongoing longleaf pine restoration programs by reducing costs for 

land clearing, hardwood control treatments, and site preparation. 

Conversion of forest lands for development also creates potential 

sources of biomass because lands slated for development in areas 

beyond hauling distance to mills are often clearcut and trees are 

either chipped and mulched or burned onsite for disposal.

SHORT-ROTATION INTENSIVELY MANAGED FORESTS

Demand for energy and bioproducts could present opportunities 

to develop dedicated bioenergy plantations. These plantations 

could produce biomass specifically for energy generation and to 

augment existing biomass resources, thus, ensuring adequate 

feedstock availability. Bioenergy plantations can be agricultural 

systems that produce herbaceous crops such as switchgrass 

(Panicum virgatum), sugarcane (Saccharum officinarum), and others 

and they also can produce short-rotation woody crops (SRWC). 

Ideal SRWC species grow quickly, produce high energy yields, and 

typically can coppice (regrow from the stump following harvest), 

which reduces replanting costs. Under coppice management, three 

to five growth stages can be harvested during the life of a tree, with 

each growth stage lasting 2 to 10 years. SRWC production largely 

resembles agriculture, often using adapted agricultural equipment 

to improve the efficiency of site preparation, planting, weed 

control, and harvest (Culshaw and Stokes 1995). SRWC plantations 

are operational in New York State and prevalent in Sweden and 

other parts of Europe. While SRWC plantations in the United States 

have been largely dedicated to the production of pulpwood 

(Culshaw and Stokes 1995), these plantations are likely to expand 

to meet future demand for renewable energy (Berndes and others 

2003, Volk and others 2004).

In the United States, 22 hardwood species have been identified 

as potential SRWCs (Ranney and others 1986). Native species 

such as sweetgum (Liquidambar styraciflua), American sycamore

(Platanus occidentalis), eastern cottonwood (Populus deltoides), 

and hybrid poplars (Populus spp.) are well adapted to the South, 

yielding 3 to 5 dry tons per acre per year. Exotic candidates for 

the subtropical South (Florida, Puerto Rico, and the U.S. Virgin 

Islands) include Eucalyptus spp., with the potential for exceptional 

yields of over 9 dry tons per acre per year (Klass 1998), and 

Leucaena leucocephala, a multipurpose tree with the potential 

to fix nitrogen and produce forage for livestock. Eucalyptus 

grandis has been produced commercially in southcentral Florida 

Leaves, grass

clippings, and

whole stumps

5% 

Chips

67%

Unchipped

logs

15%

Unchipped tops

and brush

8% 

Unchipped

mixed wood

5% 

Sold as mulch, firewood,

or boiler fuel

12%

Left, used,

or burned

on site

29%

Given

away

42%

Landfilled

17%

(A) (B)

Figure 2.5—Amounts collected by U.S. urban forestry firms by material type (A), and disposal method (B) [adapted from NEOS (1994) survey of 1,330 

respondents].
Chapter 2

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 15

since the 1970s without spreading (Rockwood 1996), and L. 

leucocephala is available in sterile varieties; however, past and 

current problems with encroachment of invasive exotic species 

may mean easier public acceptance with native species.

SRWC production systems can be designed and implemented 

to provide not only local environmental services within the WUI 

but also biomass production. For example, SRWC plantations can 

be irrigated with municipal wastewater or fertilized with treated 

biosolids or municipal compost, simultaneously increasing 

biomass production, reducing fertilizer costs, and intercepting 

nitrates and phosphates to reduce nutrient loading in waterways 

(e.g., Aronsson and Perttu 2001, Rockwood and others 2004). 

Although dendroremediation-produced biomass often contains 

heavy metals, cofiring dendroremediation-produced biomass 

with coal is cleaner than firing coal alone (Licht and Isebrands 

2005). Gasification of contaminated biomass can be optimized 

to concentrate heavy metals in a small ash fraction for proper 

handling (Vervaeke and others 2005). 

SRWC can also help build soil organic matter, recycle nutrients, 

and maintain vegetative cover to restore ecological functions on 

mined lands and other degraded lands (Bungart and Huttl 2001, 

Stricker and others 1993). SRWC established on agricultural lands 

as shelterbelts or buffer zones to protect riparian areas often 

reduce soil erosion and runoff of agricultural inputs, as well as 

improve wildlife habitat (Joslin and Schoenholtz 1997, Thornton 

and others 1998, Tolbert and Wright 1998). 

Though SRWC plantations do not provide all the environmental 

services of a less intensively managed forest, e.g., wildlife 

enhancement values associated with forest structural diversity, 

opportunities exist to apply these systems within a mosaic of 

other land uses and to land that might otherwise not be used, 

while providing beneficial environmental services and producing 

bioenergy feedstocks.

WOOD AS A FUEL

The fuel quality of WUI forest biomass used as a bioenergy resource 

is determined by its physical characteristics. These characteristics—

based on the relative contribution of leaves, needles, branches, 

stem, bark, soil contamination, and moisture content—can be 

influenced to varying degrees. For example, moisture content can 

be lowered by drying, and bulk density is a function of the size and 

other physical characteristics of the wood pieces. Volatile matter 

and the chemical composition also influence the energy content of 

the wood, commonly measured in Btus. Ash, the mineral content 

of the fuel, originates both from naturally occurring minerals in 

woody biomass and from contamination by soil. Boiler designs 

consider the ash content of the fuel, balancing heat protection for 

the grate and costly outages due to slagging and fouling (Sims 

2002). Wood ash from combustion plants can also be reapplied to 

forest lands, so that some of the nutrients removed during harvest 

can return to the soil. 

CONCLUSIONS

Woody biomass in the WUI is dispersed in a variety of forms across 

the landscape, making the availability of woody biomass difficult 

to predict. Woody biomass feedstocks tend to change over 

time due to changes in wood processing technologies, e.g., mill 

residues, harvesting technologies, landscape patterns, and market 

competition for the material. 

As discussed in chapter 3, the nature of the feedstock (high 

moisture content, variable ash content, high volatiles and 

relatively low caloric content, and variable size and shape) requires 

careful consideration in the design of harvesting, handling, and 

conversion systems. These systems are intimately connected to 

the source of woody biomass, as is the decision for the enduse 

of woody biomass and, ultimately, the amount and type of 

power generated from it (see chapter 4). The more consistent the 

feedstock, the more closely the handling system and conversion 

plant can be matched to it for greater overall efficiency of the 

plant and to avoid the extra cost associated with overengineering 

the system to handle variable feedstocks (Sims 2002). 

As discussed in chapter 5, the quantity and quality of biomass 

vary greatly by location and season. Its delivered price will be 

determined by such factors as where woody biomass originates, 

how much is available, collection and transportation equipment 

employed, and the quality of feedstock. Within the WUI, woody 

biomass is generated from forestry and forest management 

activities, urban activities, and potentially dedicated biomass 

operations. Increased demand for woody biomass generated by a 

bioenergy market may increase biomass prices, offsetting costs of 

thinning operations and enhancing opportunities for landowners 

to manage for higher value forest products. 

Locating, collecting, and securing woody biomass from the WUI 

can be logistically challenging, and strategic planning should 

consider the future directions of development and land cover 

conversion, as well as public perceptions of woody biomass 

utilization (see chapter 7). 

The development of plantations to specifically supply biomass 

and contributions from phytoremediation projects, which use 

trees and other vegetation to restore degraded land, provide 

opportunities to further increase woody biomass supplies. These 

residues—consisting of tree parts such as branches and tops 

and sometimes whole trees that are not considered saleable—

are often left onsite after harvesting operations. Many stands, 

especially hardwood stands previously degraded from poor 

logging practices, may be dominated by low quality and low-value 
Woody Biomass Sources in the Wildland-Urban Interface

16 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

timber suitable for energy production. In some cases, removal of 

this low-value timber as biomass enables landowners to manage 

for higher quality future timber products. 

To make appropriate design and scale decisions for conversion 

plants and handling systems for bioenergy projects, consideration 

of the quantity and quality of woody biomass resources available 

should be incorporated into the initial planning stage. These 

decisions impact every facet of a bioenergy project, from 

harvesting and conversion technologies to economic and social 

impacts. Careful consideration of the source of woody biomass will 

lead to more efficient use of this valuable natural resource.

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Woody Biomass Sources in the Wildland-Urban Interface

18 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

C/D debris: debris generated from construction or demolition of 

structures. C/D debris may contain land clearing urban wood 

waste removed in the process of new construction.

coppice: the ability of a tree to regrow from the stump after 

harvest.

forest residue: the aboveground materials generated from 

logging during precommercial thinnings and harvesting 

operations, e.g., leaves, bark, tops, and broken trees.

hardwood: angiosperm tree species that are characterized by 

broad leaves (as opposed to needles) and are usually deciduous.

landing: the site where logs are accumulated for loading on to 

trucks during a harvest operation.

logging residue: poor quality trees and tree components, such 

as crowns and stump-root systems that are left onsite during 

commercial harvesting operations.

merchantable timber: trees which are economically valuable to 

harvest.

Mg: megagram = 106 kilograms.

MSW: municipal solid waste collected from residences, 

commercial businesses, and governmental agencies and 

delivered to solid waste facilities for disposition or recycling. 

Urban wood waste, yard trimmings, and C/D debris may be 

considered MSW if these materials are collected, handled, and 

delivered to permitted solid waste facilities.

nonindustrial private landowner: a person owning < 1,000 

acres of forested land who is not directly affiliated with a wood 

processing plant.

nonmerchantable timber: trees which are not harvested because 

they are too small, poor quality, or are not an economically 

valuable species.

phytoremediation: the use of trees or other vegetation to remove 

contaminants, such as heavy metals, and restore degraded land.

pulpwood: trees and wood suitable for manufacturing paper; 

purified cellulose products, such as absorbents, filters, 

rayon, and acetate; and oleoresin products, such as pine 

oils, fragrances, cosmetics, and thinners (www.sfrc.ufl.edu/

Extension/ssfor11.htm).

sawtimber: trees that meet minimum diameter and stem quality 

requirements, making them suitable for conversion to lumber.

skidding: moving trees from a felling site to a loading area or 

landing, usually using specialized logging equipment.

slagging and fouling: the formation of deposits on boiler tubes, 

usually due to the presence of chemical contaminants.

softwood: coniferous tree species that are characterized by 

needlelike leaves, and are usually evergreen.

SRWC: short-rotation woody crops.

stumpage: the price paid by buyers to landowners for standing 

timber.

tipping fee: an amount paid to dispose of waste.

WUI: wildland-urban interface.

Woody Biomass Sources in the Wildland-Urban Interface

Glossary of Terms
Wood to Energy: Using Southern Interface Fuels for Bioenergy • 19

INTRODUCTION

Management of timber resources in the wildland-urban interface 

(WUI) is challenging, particularly with regard to fire control and 

product utilization. This chapter considers some of the issues 

associated with harvesting, preprocessing, and delivery of woody 

biomass in the WUI; explores the relationship of harvesting to fire 

control; reviews various harvesting systems; and examines related 

topics, including environmental impacts and regulatory issues. 

The objective is to provide land managers with information on 

methods available to harvest and transport woody biomass in 

the WUI. 

To derive maximum use of forest resources generated within the 

WUI, harvesting, processing, and delivery methods compatible 

with unique WUI characteristics must be developed. In some 

respects, these methods are similar to conventional harvesting 

of commercial forests. The primary differences involve size 

and location of tracts and types of materials harvested. These 

differences present both challenges and opportunities for 

effective biomass recovery. Nevertheless, development of efficient 

biomass recovery systems in the WUI is critical because biomass 

materials can represent a low-cost source of renewable energy.

Within the WUI, wildfire hazard is a major concern, and harvesting 

and utilization of the excess woody biomass is one of several 

alternatives for reducing fuel buildup. Prescribed burning to 

reduce fuel buildup has been the most common practice in 

conventional forestry. In many parts of the South, the WUI 

is expanding into areas of vegetation, such as upland pine 

forests, which have naturally evolved to become dependent 

on wildfire for regeneration. Because these WUI areas are more 

accommodating to development and construction, the value of 

land near urban areas has increased, leading to higher population 

densities and more roads in formerly open rural areas. Higher 

population densities within these areas make it more difficult to 

plan, implement, and control prescribed burning. In addition, 

factors such as safety, liability risk, negative public perception, 

and smoke issues are making it more difficult for foresters to 

use prescribed fire as a land management tool. But without fire, 

hardwoods encroach, pines become overly dense, and fuels 

become abundant.

Where smoke issues are a concern, mechanical site treatment can 

reduce fuel materials. One form of mechanical treatment involves 

using specialized equipment that reduces fuel loads by grinding 

and mulching vegetation at the site (Mitchell and Rummer 1999, 

2001; Rummer and others 2002; Thompson 2002). This method 

would be most cost effective when the resulting biomass material 

has no market potential and harvesting and transporting it would 

cost more than grinding in place (Stanturf and others 2003). 

Herbicides have been used to control undesirable understory 

vegetation in some managed forests. While useful in some areas of 

the WUI, herbicides are generally a high-cost option that may be 

perceived negatively by the public. Also, herbicides do not remove 

the fuel, which may increase fire hazard immediately after use.

HARVESTING WOODY BIOMASS

Some of the main factors that influence harvesting costs are the 

method used, stem size, material type, e.g., trees vs. residues, 

and amount of material removed (Hartsough and Stokes 1990). 

In general, harvesting costs per unit of material are lower with 

larger trees and higher volumes removed per ha (Holtzscher and 

Lanford 1997, Kluender and others 1997). 

Another factor in harvest cost is tract size. Land in the WUI is 

often fragmented and noncontiguous, requiring harvest methods 

appropriate for smaller stands. Conventional forest harvesting 

operations are more costly as tract sizes fall below 10 ha (Rummer 

and others 1997), due, in part, to the high cost of moving, loading, 

and relocating mechanized equipment. For small tracts, the cost 

and efficiency of using manual labor for harvesting understory 

vegetation has also been studied. Because workers are not in 

enclosed equipment cabs, safety liability is a major impediment. 

However, such labor intensive systems, with their lower capital 

investment, can be the most cost effective, especially when 

conditions or volumes within a stand restrict productivity of large 

machinery (Bolding and others 2003). 

Harvesting systems for pine and hardwood species often use the 

same machinery and techniques, with similar results. However, 

southern hardwoods are often located in lower, wetter areas. 

Consequently, less hardwood harvesting is likely to take place in 

the WUI. The exception is where undesirable hardwood understory 

is being removed. The discussion here generally applies to 

softwood and hardwood species. Harvesting systems, residue 

harvesting, and environmental issues surrounding harvesting of 

woody biomass are discussed in the following paragraphs.

Chapter 3

Harvesting, Preprocessing, and Delivery of Woody Biomass 

in the Wildland-Urban Interface

Richard M. Schroeder

Chapter 3
Harvesting, Preprocessing, and Delivery of Woody Biomass in the Wildland-Urban Interface

20 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Conventional Harvesting Systems

When considering harvesting within the WUI, existing and proven 

mechanized timber harvesting systems should be considered 

first. These systems have evolved for > 50 years to become the 

most efficient and least expensive method of removing volume 

from the forest. There are four primary functions that timber 

harvesting systems must accomplish: (1) felling; (2) processing 

(delimbing, bucking, topping); (3) intermediate transport 

(skidding or forwarding); and (4) loading (Wilhoit and Rummer 

1999). Delimbing, cutting to length (bucking), and removing the 

top (topping) are not required when harvesting biomass, unless 

the log portion of the tree is to be separated. There can also be 

an additional step, size reduction (chipping or grinding), which is 

discussed later in this chapter.

Biomass harvesting systems normally involve removing the entire 

tree, whereas conventional harvesting systems generally focus 

on only the main stem. For this reason, equipment design and 

operation are somewhat different. Work in biomass harvesting 

in the 1980s focused on adapting existing systems to harvest 

conventional products, such as saw logs and pulpwood, as well as 

residues from logging operations (Stokes and Sirois 1989, Stokes 

and others 1984). Conventional harvesting equipment, such as 

feller bunchers and skidders, were complimented with whole-tree 

chippers, flail delimbers, and grinders that allowed particle size 

reduction and collection of nonmerchantable material. By 1992, 

several fuel harvesting systems were in operation. Most utilized 

feller bunchers (generally rubber-tired), grapple skidders, and 

large chippers that operated at the landing site (Stokes 1992). 

At some mills, whole trees were delivered to the mill sites using 

trailers modified to haul trees with the tops intact. At the mill, tops 

and limbs were removed and used for fuel. During the late 1990s, 

many of these systems were discontinued due to lower fuel prices.

Hartsough and others (1995) analyzed five conventional 

mechanized harvesting systems, four of which processed the 

nonmerchantable portion as biomass fuel. These systems 

represent the most common equipment scenarios currently 

available from existing logging contractors. Studies have 

consistently shown that the most economical method of 

harvesting biomass is the integration of existing harvesting 

operations and the collection of both merchantable material and 

biomass in a single pass (Greene and others 2006, Rummer 2006) 

Following are descriptions of harvesting systems used in the 

studies:

• Feller buncher-skidder-flail/chipper: Feller bunchers cut the 

trees, and skidders delivered them to one combination flail 

delimber-debarker-chipper, where the stems were debarked 

and then chipped into pulp-grade chips. In this scenario, the 

nonmerchantable material was not processed, and was left in 

the forest. 

• Feller buncher-skidder-processor-loader-chipper: All material 

was felled with tracked feller bunchers that separated 

merchantable trees into separate piles as they were cut. The 

remaining biomass was lumped together into a second pile. 

The merchantable trees were skidded to a processor that 

mechanically delimbed, bucked, and topped the trees. Most of 

the limbs removed by the processor were left in the woods as 

they were cut or were returned to the woods by the skidders. 

The remaining material was taken to a chipper where it was 

processed for fuel.

• Harvester-forwarder-loader-chipper: This system utilized one 

harvester, a machine that processes (fells, delimbs, bucks, 

and piles) both biomass and saw-log trees in separate piles. 

A forwarder loaded both types of material and carried them 

to a landing. Saw logs were loaded with one conventional log 

loader, and the biomass was processed with a chipper. The chips 

were used for fuel.

• Feller buncher-harvester-skidder-loader-chipper: Merchantable 

trees were processed with one harvester, while the feller 

buncher cut biomass trees. Three skidders pulled both types of 

piles to a landing, where one conventional log loader loaded 

the saw logs and one chipper handled the biomass.

• Harvester-forwarder: In this system, only merchantable 

stems were harvested using harvesters and forwarders. The 

nonmerchantable biomass was left in the stand for this study, 

although this system could also be used to remove biomass in 

other applications.

Tract size may be one of the most important factors in cost of harvesting within the WUI. This was 

demonstrated in a cost-and-productivity study by the 

USDA Forest Service, Southern Research Station in 2005 in 

southern Alabama (Mitchell 2006). In an effort to enhance 

red-cockaded woodpecker habitat, small tracts of natural 

pine (Pinus spp.) were treated (in a manner similar to 

a fuel-reduction harvest) to remove the understory of 

small-diameter trees. Two 10-acre tracts were treated 

with conventional harvesting and chipping equipment. 

All trees < 7.5 inches in diameter were removed, with the 

average cut tree being < 3 inches in diameter. Researchers 

found that the operating cost of chipping biomass and 

transporting it nearly 60 miles was $11.44 per green ton, 

but the total cost of transportation, overhead, and profit 

was an additional $14 to $15 per green ton.
Wood to Energy: Using Southern Interface Fuels for Bioenergy • 21

Chapter 3

The systems described above are expensive, highly mechanized 

operations that require large volumes of material to be 

harvested each day to justify the expense. In 1995, the capital 

cost for each biomass handling system (systems 1 through 4) 

was estimated to be $1.2 to $2 million (Hartsough and others 

1995). In the first four harvesting systems, from four to eight 

separate pieces of equipment were transported to each site 

(each requiring a tractor and trailer), significantly adding to 

overall costs and making them less cost effective for harvest of 

small- or low-volume tracts, such as those that are to be thinned 

(Willhoit and Rummer 1999). 

One disadvantage of conventional, large-scale harvesting 

systems, is that individual machines often are designed to 

operate best under a limited variety of operating conditions. 

The WUI often contains a wide variety of conditions related 

to stand density, terrain slope, and average tree size. In the 

previously described conventional harvesting systems, as many 

as three skidders and two feller bunchers were sometimes 

required to keep up with one processor. The exception was the 

harvester-forwarder (system 5) or cut-to-length (CTL) system. 

The CTL system is often used in thinning or in sensitive areas 

where minimizing damage to residual trees is critical. In these 

situations, the CTL system causes less damage to residual trees 

than systems that remove longer trees. However, the CTL system 

is rarely used in clearcutting or in thinning plantations because 

it is generally more expensive than tree length operations. 

Harvesting costs for the CTL system are greatly affected by tree 

size, especially if only the portion of tree suitable for pulpwood 

or saw logs is removed. On a weight basis, cost for harvesting 

trees 4 inches in diameter has been estimated to be 2 to 2.5 

times more than harvesting 6-inch diameter trees, and more 

than 3 times the cost of harvesting 10-inch diameter trees 

(Holtzscher and Lanford 1997). 

The CTL system has been combined with a small chipper to 

harvest biomass for energy (Bolding and Lanford 2001). In this 

operation, nonmerchantable trees are felled and piled during 

the harvest, along with limbs and tops from merchantable 

trees. A forwarder transports the nonmerchantable material 

to a chipper and the merchantable logs to log trailers. The 

chipper is smaller than traditional whole-tree chippers 

used in conventional harvesting systems, and more closely 

matched to the capacity of one harvester and one forwarder. 

For regenerated stands, the economics of the system include 

reduced site-preparation costs and the value of the material 

harvested in terms of energy content. In stands where biomass 

needs to be removed, the treatment value in reduced sitepreparation costs can be 25 to 50 percent of the harvest value 

(Rummer 2006). Bolding and Lanford (2001) determined that 

the CTL approach was cost effective under a stand conversion 

scenario where site-preparation costs were a factor. This system 

is quite capital intensive (estimated capital cost is $749,000), but 

fewer pieces of equipment and a smaller chipper make it more 

mobile than other conventional systems.

The previously described systems were based primarily on 

conventional logging equipment designed for large tracts of 

industrial forest. Over time, these conventional harvesting 

systems have become larger, more capital intensive, and 

better designed for large tracts of land. They also represent 

the systems commonly available to land managers considering 

harvesting within the WUI. 

Small-scale Harvesting Systems

As demand for harvesting systems within the WUI increases, 

new systems better suited to small operations are being developed. Systems that employ machines with multiple functions 

will allow for fewer pieces of equipment and will be less expensive to move in and out of stands, so relocation will be more 

economical. Small equipment may be another consideration 

because more than one unit can be moved on a single large 

transport trailer (Stanturf and others 2003).

Small systems, such as the once common single-axle 

pulpwood truck and the manual chainsaw feller, are now rare 

in commercial pulpwood harvesting operations. Small-scale 

operations using manual chainsaw felling and either cable 

skidders or animals for skidding are still used for sawtimber 

harvests, especially in situations where volume is low, terrain 

is restrictive, or aesthetics are a major concern. Logging 

operations in urban areas of the Southern United States often 

use manual felling, trucks, and loading equipment designed for 

handling lengths cut for pulpwood. 

Small and multiple-function equipment has been examined 

for use in biomass harvesting for several years. In analyzing 

the feasibility of using a multifunction machine, the fact that 

it can only perform one function at a time must be taken into 

consideration. In 1986, Stokes and Sirois evaluated a chipperforwarder, which chipped wood in the field into an onboard 

container. The chips were transported in the container to a 

landing. Chipper-forwarders are not in common use in the 

United States today because of the relatively low value of the 

chips when used as fuel. However, they have been adopted 

in other parts of the world where higher fuel prices make the 

system more economical.

Efforts have been made to investigate new, small harvesting 

systems, often through modification of agricultural or industrial 

machines. Two primary objectives in developing small-scale 

timber harvesting systems are low capital investment and 

small physical size (Wilhoit and Rummer 1999). Because of 

low productivity and safety concerns, alternative small-scale 

systems must include mechanized felling and, preferably, 
Harvesting, Preprocessing, and Delivery of Woody Biomass in the Wildland-Urban Interface

22 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

mechanized processing as well. For optimum small-scale 

mechanized harvesting systems, the following machines should 

be considered:

• Four-wheel-drive farm tractors, small rubber-tire skid-steer 

machines, and larger rubber-track skid-steer machines

• Hydraulic shears for felling

• Harvester heads for processing, and

• Front loader or small knuckleboom attachments for loading

Today, many manufacturers are designing and manufacturing 

smaller scale harvesting equipment. In a recent trade publication, 

six manufacturers advertised harvesting attachments and carrier 

modifications for farm tractor or skid-steer machines, and nine 

manufacturers offered smaller scale chippers for use in timber 

harvesting (Forest Products Equipment 2005). 

The use of livestock in timber harvesting systems (principally 

horses or mules) has nearly disappeared from commercial forestry 

in the United States. However, it may be reevaluated for use in 

some areas of the WUI where conventional harvesting equipment 

creates objectionable noise, traffic, or visual impacts. This method 

of harvesting may be more appealing to small landowners 

because it has lower impact during use and potentially causes 

less damage to residual trees. 

Forest harvesting using animals is labor intensive. In addition, 

animal logging is perhaps more susceptible to interruptions 

by weather than mechanized logging. A 1999 study of animal 

(horses and/or mules) logging crews in northern Alabama found 

that, in general, animal loggers worked < 30 miles from home, 

and most moved their animals to the logging site each day and 

back home each night. The percentage of time spent working 

during a day ranged from 64 percent (owners) to 45 percent (crew 

members); the animals were only used 22 percent of the time 

(Wilhoit and Rummer 1999). 

In countries with low labor costs, animal skidding for small-tree 

harvesting, particularly in thinning operations, is less expensive 

than machine skidding. This is not true for countries like the 

United States where labor costs are high. However, animal 

harvesting systems are less effective than machine skidding 

when the terrain is irregular and there is a high possibility of 

severe weather conditions. Long skidding distances are not 

conducive to the use of animals because of low ground speed 

(Wang 1999). Animal logging requires specialized support 

equipment and skilled and experienced operators (Rummer 

1996). Such methods may be applied to the WUI, but success in 

using this type of operation will depend upon abilities of locally 

available contractors.

RESIDUE HARVESTING 

Forest residue is the woody biomass left onsite after the 

harvesting of merchantable stand and tree components is 

complete. This is sometimes referred to as “logging slash” and is 

usually considered unsuitable for traditional products such as 

pulpwood or sawtimber (Stokes and Sirois 1989). Residue in the 

WUI may also include material generated from urban activities 

such as land clearing and tree debris generated from landscape 

maintenance, utility line clearance, and removal of tree debris 

from storms. 

Two studies evaluated many of the available means and methods 

for recovery of forest residues, both in European and North 

American countries (Stokes 1992, Stokes and Sirois 1989). The 

studies indicated that conventional harvesting systems were 

most often used, and that grinding small pieces, such as tops and 

limbs at landings, was done using tub grinders and vertical feed 

hammer mills. These machines produce material with different 

particle sizes, which determines the amount of processing 

required at the end-user facility and may affect value of the 

delivered material. Particle sizing is discussed in the preprocessing 

section of this chapter. 

In general, logging slash is less than one-quarter the density of 

solid wood (Rummer and others 2004) and weighs approximately 

135 pounds per cubic yard (Rummer and others 2004). The 

productivity of any handling operation (hauling, skidding, and 

loading) is reduced by this low-density material, increasing 

harvesting and transportation costs per ton. The Florida Organics 

Recyclers Association (1996) estimates that the density of loose 

mixed brush generated from urban activities (which in many ways 

resembles conventional logging residue) is 100 to 250 pounds per 

Removal of biomass as part of a conventional harvest is considered the most viable option in terms of cost 

and value. However, harvesting contractors question the 

impact on cost and productivity of adding a chipper and 

removing biomass during the harvest of conventional 

merchantable material. In a study using conventional 

equipment, biomass understory within a 33-year-old pine 

(Pinus spp.) plantation in southern Georgia was removed 

and chipped as part of a harvest of merchantable material 

(Greene and others 2006). Biomass included softwood and 

hardwood tops, branches, and undersized trees from 1 to 

4 inches in diameter. About 15 green tons per acre of both 

tops and small trees were harvested. Results showed that 

daily production of roundwood was not decreased by the 

added production of biomass if at least 1 load of biomass 

could be harvested for every 10 loads of merchantable 

material.
Chapter 3

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 23

cubic yard. This is probably representative of the southern region. 

In comparison, stacked pine pulpwood has a density of > 1,000 

pounds per cubic yard.

Finding an effective method of densifying residues would reduce 

the cost of biomass collection. As early as 1987, the use of 

conventional round balers for collecting residues was examined 

by several researchers (Curtin 1987, Stokes and others 1987, 

Woodfin and Stokes 1987). These studies showed that while 

baling the residues was possible, the material sometimes needed 

to be crushed prior to baling (see preprocessing section of this 

chapter), and that bales often required hand feeding into the 

machine. To date, residue baling using conventional equipment 

has not been widely adapted.

Stokes and others (1987) reviewed a 1982 study that addressed 

increasing bulk density of loads of smaller diameter pieces 

harvested during thinning operations. Two experimental 

trailers were built that could compress the load using hydraulic 

compacting devices. In most cases, load compression was 

increased by 50 to 100 percent for softwoods and somewhat less 

for hardwoods. Results were better when low-moisture material 

such as field-dried biomass was used. However, transport costs 

for compressed loads on a per ton basis still tended to be higher 

because equipment costs were higher and the trailers were 

heavier, allowing less load capacity. 

Much of the work dealing with machinery that compresses 

loose forest residues into uniform bundles has been done in 

Scandinavian countries. A bundling machine, coupled with 

a forwarder designed to handle the bundles, was tested in 

the Western States by the Forest Service (Rummer and others 

2004). The bundler was a rubber-tired machine that collected, 

compressed, and bound forest residues into cylindrical bundles 

approximately 2 feet in diameter and 10 feet long. This simplified 

handling residues by compacting loose slash into a form that 

resembles a log. The forwarder then loaded the bundles and 

delivered them to a landing for transport. The study showed that 

such a system may be competitive with other forms of harvesting 

residue, but that the residues had to be properly placed on the 

ground to be effectively bundled.

ENVIRONMENTAL ISSUES 

Harvesting operations, in general, have come under scrutiny and 

are the subject of controversy as a result of their adverse effects 

on the environment. Harvesting practices within the WUI can be 

expected to come under the same if not more scrutiny because 

they will often be more visible to the public.

Harvesting usually involves moving machinery or livestock teams 

over forested areas and removing biomass by cutting, lifting, 

and moving. Animal logging generally has less site impact than 

mechanized logging. The amount of machinery traffic on the 

site is a function of the intensity of harvesting. In a 1998 study 

of clearcut harvesting in loblolly pine plantations in northern 

Alabama, the use of Geographic Information System tracking 

on equipment showed that 25 percent of the stand incurred no 

traffic, 50 percent had one to five passes, and 25 percent had 

more than five passes. The number of passes was not clearly 

correlated with measured soil properties after the harvest 

(McDonald and others 1998).

When comparing harvesting methods such as single-tree 

selection, group selection, shelterwood, seed tree, and clearcuts, 

single-tree selection resulted in the most undisturbed soil area 

(39.4 percent) following harvest, while 9.1 percent of the seed tree 

and only 6 percent of the clearcut area remained undisturbed. 

Investigators reported that soil was most exposed in clearcut 

harvests (19 percent), followed by group selection (13.4 percent), 

shelterwood (13.3 percent), seed tree (12.7 percent), and single 

tree (11.8 percent) (Stokes and others 1995). Soil disturbance can 

result in higher levels of erosion, but exposed soil can be helpful 

in promoting natural regeneration, and can promote or accelerate 

the return of desirable species.

The environmental effects of biomass harvesting have not been 

extensively studied, but the impact may be similar to wholetree harvesting, where entire trees with tops intact are removed 

and chipped. Whole-tree harvesting versus conventional stem 

harvesting has been studied for effects on nutrient losses and 

regrowth (Johnson and Todd 1987, Johnson and others 1988, 

Mann and others 1988, West and others 1981). Integrating 

biomass chipping and removal with the harvest of conventional 

products means that tops and branches normally left on the forest 

soil are removed from the site. A study conducted in slash pine 

plantations in southern Georgia examined what the total nutrient 

loss would be after harvest. Results indicated that if tops from 

all merchantable trees were removed, an additional 6.48 pounds 

of nitrogen, 0.52 pounds of phosphorus, and 1.73 pounds of 

potassium per acre would be removed, compared to harvesting 

only merchantable logs. When small trees (normally left behind) 

and tops from merchantable trees were removed, total nutrient 

losses were 24 pounds of nitrogen, 2.5 pounds of phosphorus, and 

7.1 pounds of potassium per acre (Westbrook and others 2006).

Another Georgia study evaluated the effects that various sitepreparation techniques had on nutrient losses when comparing 

conventional harvesting to whole-tree harvesting. Researchers 

found that in the southern Piedmont and Coastal Plain 

ecosystems, the method of site preparation had greater impact on 

nutrient losses than harvest method. Site-preparation techniques, 

especially the shear-pile-disk method, accounted for the highest 

loss of available nutrients, regardless of harvesting technique 

(Gaskin and others 1989). 
Harvesting, Preprocessing, and Delivery of Woody Biomass in the Wildland-Urban Interface

24 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Nutrient loss from any method of biomass harvesting may be 

offset by modifying site-preparation techniques to minimize 

soil disturbance and nutrient losses. On tracts of land where 

clearcutting and planting are practiced, if biomass harvesting 

can reduce the amount of residual material being handled 

during site preparation, less soil disturbance should take place, 

and the net effect on soil conditions and site productivity may 

actually be positive. 

PREPROCESSING BIOMASS

To facilitate efficient transport, material handling, and 

utilization at the conversion facility, biomass is preprocessed 

during or after harvesting. The optimum treatment depends 

on characteristics of the material, the end use, and sitemanagement requirements. In this discussion, preprocessing 

will address two critical characteristics of biomass: particle size 

and moisture content.

Particle Size

For nearly all end uses, ultimate material handling requires uniform 

particle size. Large-scale conversion facilities usually have additional sizing and classifying equipment onsite, but initial sizing 

often takes place prior to transport (exceptions include bundling of 

residues and transporting whole trees). 

Particle sizing is often integral to biomass harvesting. Because 

of the diversity of biomass material taken from the WUI, some 

consideration of particle sizing technology is helpful. Forestry 

residues are usually processed to reduce the material size for 

economical removal, transport, and handling. Size reduction 

can assist in decreasing transport costs by increasing density of 

shipped material and decreasing air space in transported loads. 

Studies have shown that chipping of logging residues resulted 

in a 25-percent decrease in hauling costs (Stokes 1998).

There are still only a few commonly used methods to turn 

large pieces of woody material into small pieces. The following 

general categories of biomass size-reduction equipment can 

be used for comparison (Goldstein and Diaz 2005): chippers, 

which cut up material with a slicing action; grinders, which 

reduce particle size by repeatedly striking them with hammers 

or cutting heads; and shredders, which generally tear particles 

apart by shearing.

The most common size-reduction equipment in forestry is the 

chipper. Chippers are characterized by high output, highspeed cutting blades or knives. Most can also throw chips 

into transport trailers for hauling. Chipper knives must remain 

sharp and are susceptible to wear from high soil content, 

metal contamination, or rocks and stone. Because of this, 

when chipping dirty material, they require replacement and 

sharpening more often, which results in increased maintenance 

and machinery downtime. Chippers are well integrated into 

existing harvesting systems because they are built to accept 

material of any length.

Grinders are types or derivatives of hammer mills, a type of 

machinery that evolved from milling processes for grains, meals, 

and powders. Forestry applications include horizontal feed 

grinders (material fed to hammers horizontally) and vertical feed 

grinders, such as tub grinders. Grinders are better at handling 

contamination than chippers, and they accept a wider range of 

piece sizes. Tub grinders are designed to take short, nonoriented 

pieces, including stumps, tops, brush, and large forked branches. 

Grinders rely on hitting a piece of wood (usually with high-speed 

rotating hammers) often enough to finally break it into the desired 

particle size. They require more energy than chippers per ton of 

output, and excessive soil can increase internal wear.

Shredders are generally slow-speed rip/shear devices used widely 

in tire shredding. Material is pinched between rotating devices 

and ripped apart or sheared. Shredders are useful when material 

is contaminated, e.g., with metal, rock, or concrete, because the 

internal parts are slow moving so damage to equipment can be 

avoided. Shredders are not used widely in biomass operations 

except as a first-stage size reducer because their capital cost is 

high and the particle size they produce is larger and less uniform 

than other options. Material from shredders usually requires 

further size reduction.

The desired particle size is determined by the buyer or end 

user. Generally, the size must be small enough to be conveyed 

using chain or belt conveyors, augers, or feed hoppers without 

interlocking or stringy pieces jamming the equipment. Typical 

conveying equipment used by the forest products and biomass 

combustion industries readily handles material that is < 3 inches in 

length. This can be accomplished with either chipping or grinding.

Moisture Content

Much of the biomass harvested for energy has been used as solid 

fuel for direct combustion, and the benefits of having drier fuel for 

this purpose are well documented. Dry fuel in a direct combustion 

boiler improves efficiency, increases steam production, reduces 

ancillary power requirements, reduces fuel use, lowers emissions, 

and improves boiler operation (Amos 1998). 

Transpirational drying, also known as leaf seasoning, biological drying, and delayed bucking, occurs when felled trees are left in the 

forest for several weeks with the tops, branches, and leaves intact 

(Stokes and others 1993). The findings of some studies on transpirational drying are summarized below: 

• In the upper Piedmont of Georgia, red oaks (Quercus rubra),

sweetgum (Liquidambar styraciflua), and yellow poplars 

(Liriodendron tulipifera) were dried with tops intact for up 

to 8 weeks. Most moisture loss occurred in the first 3 weeks. 
Chapter 3

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 25

Oaks had the least moisture loss, from 43 to 39 percent, and 

sweetgum had the highest moisture loss, from 54 to 39 percent 

(McMinn 1986).

• Drying 6-inch d.b.h. eucalyptus (Eucalyptus spp.) trees in Florida 

for 4 weeks resulted in moisture content reduction from about 

55 to about 43 percent at the base of the tree, and from 55 to 38 

percent at the top of the tree (McMinn and Stubbs 1985). 

• Loblolly pine (Pinus taeda) trees 5 to 9 inches in diameter were 

dried for 2 weeks near Gainesville, FL. The moisture content was 

reduced from 52 to 48 percent (McMinn and Taras 1983). 

• One of the few large-scale studies of transpirational drying was 

conducted in southern Alabama in 1987. Several hundred trees 

were felled for the study, and results were grouped by species, 

diameter, and drying time. Most drying occurred during the first 

50 days (soft hardwoods dried within the first 30 days, and hard 

hardwoods within the first 40 days). Moisture contents after 

that period were about 37 percent for pine, 33 percent for soft 

hardwoods, and 32 percent for hard hardwoods (wet weight 

basis) (Stokes and others 1987).

Transpirational drying is important from the standpoint of 

transport costs and combustion efficiency. Typically loads reach 

maximum legal weight limits before they are filled to their 

maximum volumes. Thus, using drier and lighter wood usually 

allows a load to carry a greater volume of wood per load and more 

wood per load on a dry weight basis. This reduces the transport 

cost per unit of wood, as well as the amount of water being 

handled, transported, and evaporated through combustion.

Additional research was performed on a prototype roller crusher. 

This machine was designed to crush round, small-diameter stems 

and facilitate drying by opening the wood to transpirational 

drying. Results indicated that crushing facilitated drying 

during periods when rain was absent and that most drying was 

completed in the first 5 weeks after treatment. However, the study 

found no guaranteed benefit from crushing trees to increase the 

rate of moisture loss over long drying periods or during times of 

heavy rainfall (Sirois and others 1991). 

Another approach to drying involves leaving chipped material 

in the woods prior to shipping. Storing biomass in piles presents 

problems not always found in piling other material such as clean 

pulpwood chips. Bark and foliage in the biomass greatly increase 

the rate of deterioration. In one study, chips from whole trees 

developed much more heat in a pile than clean wood chips, and 

decay rates for mixed hardwood chips in an outside pile were 

reported to be three times that for clean, debarked chips (Springer 

1980). In addition, piling of chipped green biomass can lead to 

other problems in the WUI. Moving of chip piles by operators can 

result in generation of dust that is harmful to operators. Mulch and 

composting operators have reported the presence of molds or 

fungi in piles, e.g., Aspergillus spp., that may pose respiratory health 

risks. Piles can also develop sufficient heat to present a potential 

hazard from spontaneous combustion. In addition, the cost of 

returning equipment to load biomass piles at a different time than 

the harvest leads to higher overall delivered costs.

Biomass drying can also be accomplished after delivery to the 

processing or conversion facility. In many cases, these facilities 

generate heat through combustion for electrical generation or 

other purposes. This often results in heat exhaust or excess lowpressure steam (waste heat) that can be used to further dry the 

material if the facility installs proper heat transfer equipment. 

The design and effectiveness of biomass drying through waste 

heat is dependent upon the particular conversion facility. Some 

processes, such as gasification or pyrolysis, benefit greatly from 

drier biomass, while other technologies, such as hydrolysis, 

may actually require high amounts of water to be effective. 

Consequently, the conversion facility makes decisions and capital 

investments regarding waste-heat drying. Further information 

about drying technology at conversion facilities is available in a 

review by Amos (1998). 

DELIVERY METHODS 

Most forestry products and harvested material are transported by 

truck. About 80 percent of the pulpwood delivered to U.S. mills in 

1996 arrived by truck (McDonald and others 2001). Truck transport 

is usually the least expensive, but rail had a greater role in past 

years, particularly in large pulpmills or power plants with extensive 

rail facilities.

Biomass is almost always placed into a truck while in the forest, 

so the cost of handling and loading is already incurred. Rail and 

barge transportation require more handling of the biomass 

as material is moved from truck to barge or railcar and finally 

unloaded at the facility that will use it. These additional handling 

steps can add $3 or more per green ton to total freight costs. The 

cost per ton-mile for either rail or barge varies considerably and is 

dependent upon local availability. Because of added cost for extra 

handling, limited availability, and high variability in rail or barge 

freight rates, these options have a higher cost and are less efficient 

than trucking. Consequently, the remainder of this section will 

focus on truck transportation. 

Transportation of conventional forest products accounts for 

about 25 to 50 percent of the cost of delivering materials to forest 

product mills, and this percent will likely increase as fuel prices 

escalate (McDonald and others 2001). Because biomass material 

has little to no value prior to harvest, the percentage of total cost 

in freight for biomass may be even higher than these values. 

Rummer (2006) concluded that transportation is the highest single 

component of total cost for delivering biomass. 
Harvesting, Preprocessing, and Delivery of Woody Biomass in the Wildland-Urban Interface

26 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Because transport makes up the largest portion of overall cost, 

studies have been conducted to increase transport efficiency. 

Locating, moving, loading, hauling, unloading, and returning 

transport vehicles are all logistical challenges for removing 

biomass material from the forest. Coordination between truck 

availability and rate of harvesting is important. The method of 

dispatching trucks to logging sites can affect productivity and 

associated costs, so trucking capacity must closely match logging 

capacity (McDonald and others 2001). Trucks with fixed-body 

lengths that do not pull trailers (and have removable rolloff pallet 

racks to supply small-scale users) have been tested, but results 

showed that more than one small-scale supplier may be needed 

to optimize the system (Rummer and Klepac 2003). Conventional 

trash rolloff containers have also been tested for hauling logging 

slash from harvesting sites in Montana. Results showed that 

coordination between the grinding, loading, and transport 

functions was critical to the economic feasibility of this method 

(Rawlings and others 2004).

Transport Equipment 

The following is a review of transportation equipment likely to be 

used to move forest material in the WUI.

Trucks—As discussed, most biomass from the WUI is initially 

loaded into a truck and transported on existing roadways. Trucks 

for transporting commodities generally can be placed in one of 

two categories: fixed trucks and road tractors. 

Fixed trucks are vehicles with a fixed cargo box, such as a local 

delivery truck or rental moving truck. Fixed trucks are for the most 

part < 40 feet in length, and the payload capacity is less than road 

tractors. Road tractors are designed to pull cargo trailers. These 

trucks are designed for greater capacity and offer the versatility 

of changing the type, size, and configuration of cargo space. Most 

goods in the Southern United States are currently transported 

in 80,000-pound gross vehicle weight (GVW) road tractor-trailer 

combinations. 

Fixed trucks are usually shorter than road tractor-trailer 

combinations and allow more maneuverability in tight areas. 

Because of the lower payload capacity, fixed trucks are best when 

hauling distances are shorter.

Log or Bunk Trailers—This type of trailer is designed to haul trees, 

poles, or pulpwood in racks. They are lightweight and have high 

payload capacities. Residue bundles can also be transported in 

these types of trailers (Rummer and others 2004).

Vans—These tractor-trailer combinations are enclosed box trailers 

with their own axles and are most commonly seen transporting 

various types of cargo. Although some vans are watertight and 

even refrigerated, the ones used for transporting biomass are open 

at the top and not watertight.

Vans for forestry work are also known as “bulk vans” or “chip vans.” 

Bulk vans have either an open end or an open top. Open-top bulk 

vans are usually loaded with front-wheel loaders from the side 

or from overhead bins. Open-end bulk vans are generally loaded 

directly from the rear by chippers that throw the material into the 

van. Depending upon weight of the road tractor and the trailer 

itself, a payload of about 42,000 to 52,000 pounds can be carried 

in most vans. For some cargo, volume capacity is more important 

than gross weight because the material is so light that, even when 

the vans are full, they may be carrying a payload less than the legal 

capacity. Most bulk vans carry between 100 and 135 cubic yards, 

although specialty chip vans for extremely light material, such as 

planer shavings, can hold 150 cubic yards or more. 

Bulk vans can be unloaded using truck platforms that lift the truck 

and trailer and dump the material out the rear of the van, or by 

integral hydraulically operated self-unloading floors (called “live 

floors”) that move the contents from inside to the rear and out of 

the tailgate. There are many advantages to self-unloading vans, 

including the flexibility of unloading in any location and the ability 

to handle a wide variety of loads. However, live-floor bulk vans 

are heavier than regular bulk vans, and this reduces the potential legal-weight capacity of the payload. Bulk vans are generally 

considered to be the most cost-efficient mode of transporting 

preprocessed biomass, but they are difficult to move into some 

harvesting areas because of poor road conditions. In these less 

accessible areas, other options such as container trailers should be 

considered (Rawlings and others 2004). 

Container trailers—Container trailers handle most of the international trade that is moved by truck from ports, and this type of 

trailer also transports a large portion of the collected solid waste in 

the United States. The containers, which consist of a trailer chassis 

with a removable cargo box, vary in size, construction, and volume. 

The chassis can be designed to load and unload containers. Two 

common varieties are rolloff trucks or containers commonly used 

for collecting and hauling solid waste, and cargo trailers used for 

distributing goods from ships.

Container trailers are designed to hold bulk material and to be 

handled when fully loaded. They can be left on a site, filled as 

desired, and then removed and replaced with an empty container. 

Container trailers can also be used for storage of any delivered 

materials at the end user’s site. 

The distance from biomass site to handling facility and the 

time required for operation affect the cost of transportation. 

Inaccessible harvesting sites and inadequate unloading facilities 

are factors that can increase costs. Rummer (2006) estimated 

biomass transport costs of $3.50 to $4.50 per green ton for 

distances up to 40 miles and $0.12 to $0.15 per ton-mile for longer 

distances. The fixed amount for the first 40 miles reflects the lost 

time in loading and unloading. 
Chapter 3

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 27

REGULATORY ISSUES

Because of their closer proximity to more populated areas, WUI 

management activities are often more visible than conventional 

forestry operations conducted on large tracts or in remote areas. 

As a result, regulations regarding harvesting, preprocessing, and 

delivery may play a large role in developing appropriate practices 

for particular sites. Such regulations can impact landowner profits 

by increasing harvest costs and lowering stumpage prices (Spink 

and others 2000). They also can conflict with other regulations 

and ordinances. 

In the South, local ordinances related to timber harvesting 

increased 345 percent from 1992 to 2000 and occurred in all 

Southern States except Kentucky, Oklahoma, and Tennessee 

(Jackson and others 2003). Ordinances generally fall into one of 

five categories: (1) environmental protection, (2) tree protection, 

(3) public property protection/safety, (4) timber harvesting, 

and (5) special feature protection. In a survey of 13 Southern 

States, protection of public roadways and public safety were the 

predominant objectives for timber harvesting regulations (Spink 

and others 2000). Timber harvesting ordinances, specifically 

restricting forestry and silvicultural operations, accounted for 

about 10 percent of the identified ordinances in 2000. Most of 

these contained requirements for management plans, harvesting 

permits, adherence to best management practices, and 

protection of streamside management zones. Ordinances in the 

category of public property protection also impact harvesting 

operations. These include load limits on roads, road damage, 

mud and logging debris, and restrictions against interfering with 

traffic flow. Special feature ordinances adopted to protect scenic 

or environmentally valuable areas were the next most common 

category and sometimes included tree cutting prohibitions and 

the requirement to obtain a cutting permit.

The number of regulations is increasing, as the survey revealed 

that of the 346 ordinances identified in the southern region, > 80 

percent had been enacted in the last 10 years, and 44 percent in 

the last 5 years. In response to the many local ordinances, some 

Southern States have enacted “right to practice” laws. These laws 

are designed as mandates to ensure that forest landowners can 

continue to practice forestry. As of 2000, Kentucky, Virginia, and 

North Carolina had passed “right to practice” laws with varying 

levels of success (Spink and others 2000). In 2002, Georgia 

passed a law providing statewide consistency in county logging 

ordinances and set guidelines for counties to follow if they elect to 

enact local ordinances (Jackson and others 2003).

Within the WUI, local tree removal and tree protection ordinances 

related to tree size and tree replacement may be an issue to 

consider. Normally, most urban tree protection ordinances do not 

apply to forested areas in the WUI. However, when small, highly 

visible areas in the WUI are considered for harvesting, the local 

arboriculturist may become involved in the process.

In addition to local and State regulations, the Federal Government 

regulates highway transportation. The applicable rules pertaining 

to truck size, truck weight, and route designations are the 

responsibility of the U.S. Department of Commerce and the U.S. 

Department of Transportation. Among other things, these rules 

specify the minimum restrictions that States can require on most 

improved highways that are partially funded with Federal highway 

money. In general, over-the-road tractor-trailer combinations can 

be up to 102 inches in width and 48 feet in length and have a total 

maximum weight of 80,000 pounds. States may enact width and 

weight limits that exceed the Federal standard. Most Southern 

States have adopted the legal minimum as their guidelines for 

legal loads, although weight and width restrictions are sometimes 

lifted for special circumstances, e.g., fire salvage and storm 

cleanup. The maximum weight is the GVW or the weight of both 

the payload and the vehicle. Transportation companies often 

spend more for lighter trucks and trailers because of their greater 

legal payload capacity. 

Biomass for energy is often examined in the context of net energy gain, or energy balance. The amount 

of energy required to produce another unit of energy 

determines both the economic feasibility and the longterm practicality of any energy system. In a study of 

harvesting understory biomass, including tops and 

branches of harvested trees, Green and others (2006) 

determined that it took about 0.86 gallons of diesel fuel 

to harvest, chip, and load 1 green ton of biomass fuel at 

50-percent moisture content. Assuming a freight distance 

of 30 miles and average payloads and fuel efficiency of 

5 miles per gallon, an additional 0.24 gallons of diesel 

fuel was used to transport each ton. Thus, a total of 1.1 

gallons of diesel fuel was consumed to harvest and deliver 

1 green ton of biomass. If only the amount of diesel fuel 

used for harvest and transport is considered, and a green 

ton of biomass has a net heating value of 5,740,000 British 

thermal units (Btus), while a gallon of diesel fuel has a 

net heating value of 115,000 Btus, then biomass from the 

forest understory can produce > 45 times the net heating 

value of the diesel fuel it took to harvest and deliver it [fuel 

values from U.S. Department of Agriculture Forest Service 

(2004)]. Another study dealing with removal of understory 

in a natural longleaf pine (Pinus palustris) stand showed 

that the carbon harvested in fuel chips far offset the carbon 

used by fossil fuel consumption during harvest, resulting 

in a potential net carbon offset of 1.47 to 6.2 tons per acre 

harvested (Condon and Putz, 2007).
Harvesting, Preprocessing, and Delivery of Woody Biomass in the Wildland-Urban Interface

28 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Exceptions to weight and width limits can be made with special 

permits. These permits allow oversized loads to travel on the 

roads but limit their activities. In most Southern States, oversized 

vehicles are limited to traveling during daylight hours, and in 

some States, they cannot travel on holidays and weekends. These 

limitations often apply to vehicles moving harvesting machinery, 

thus adding to the cost of moving harvesting operations from one 

site to another. 

In some jurisdictions, State and Federal incentives may be 

available for removal of understory as part of a forest health 

initiative or wildfire prevention strategy. The Forest Service or State 

forestry agency may help offset the cost of biomass removal to 

improve harvest feasibility, particularly in the WUI. These agencies 

will provide guidance on available funding and policies.

CONCLUSIONS

The biomass generated within the WUI is a potential source of 

renewable energy, especially for energy consumers in urban areas. 

Tops and branches from merchantable harvests, nonmerchantable 

timber trees, and understory vegetation all present opportunities 

for biomass accumulation, fire hazard reduction, increased stand 

productivity, and reduced site-preparation cost. Many variations 

of conventional harvesting systems have been tested, and 

combining biomass harvesting with conventional harvesting 

operations appears to be the most economical option. 

The size of tracts that need to be treated in the WUI may be 

smaller than those normally harvested, which can greatly increase 

costs, especially if conventional harvesting equipment is used. 

Currently available equipment for transporting biomass from the 

WUI is the same as that used in conventional forestry operations. 

Innovation in transport methods, including increasing bulk 

density and use of transpirational drying, has the potential to 

make biomass harvesting from forest residues more attractive. 

The environmental impact of biomass removal is a complex issue 

that requires further study. Initial research suggests that removal of 

biomass from the stand may not result in significant deterioration 

in soil properties or in nutrient loss, but data is limited. 

Harvest of biomass fuel from forest residues, nonmerchantable 

timber, and urban tree debris may represent a significant 

opportunity to generate a substantial amount of net energy, 

because the net heating value of the biomass fuel produced greatly 

exceeds the fuel used in harvest and transport of the biomass 

materials. Managers considering harvest options for WUI stands 

should investigate local and State transportation regulations, as 

well as local ordinances that affect harvesting operations. 

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Harvesting, Preprocessing, and Delivery of Woody Biomass in the Wildland-Urban Interface
Chapter 3

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 31

bulk van: a type of trailer designed to transport bulk unpackaged 

goods, usually loaded from the top or from the rear.

bundler: a machine designed to lift forest residue, wrap pieces 

into a bundle, secure the bundle with twine, cut each bundle 

into desired lengths, and eject the bundle onto the ground.

chain flail debarker: a machine designed to remove branches and 

bark by passing stems through a series of high-speed swinging 

chains. Chain flail debarkers can include a loader or be loaded 

by another machine.

chipper: a machine, either stationary or mobile, designed to 

reduce tree stems or whole trees into wafer-shaped pieces or 

chips, using sharp knives.

chip van: a type of bulk van designed to transport forest products, 

generally with lighter weight construction and higher volume 

capacity than other bulk vans.

cutter head: a device mounted on a mobile machine designed to 

cut trees at ground level using a hydraulic saw.

delimbing gate: a heavy steel grate with large holes, often over 

16 feet in length and 6 feet in height, positioned vertically in the 

forest, to remove limbs from whole-tree stems. 

feller buncher: a rubber-tired or track-mounted machine 

designed to cut trees and accumulate cut stems into piles. Feller 

buncher cutting heads can be attached directly to carriers that 

drive up to a tree to cut it (drive-to-tree), or the cutting head 

can be attached to a swinging boom and reach to a tree to cut it 

(swing-to-tree).

forwarder: a machine designed to load cut trees or processed 

material from the ground and transport it to a landing for 

further processing or loading into transport vehicles. 

grapple: a device designed to grasp a tree or log between two 

arms and lift or move the piece. Grapples are located at the rear 

of grapples skidders, where they grab the stems and hold them 

while the skidder drags them from the woods.

harvester: a rubber-tired or track-mounted machine that 

performs the functions of the feller buncher and the processor.

knuckleboom: a boom extending from the main chassis of a 

machine used to support a cutting device or grapples for 

loading material.

processor: a machine designed to delimb, buck to length, and 

place stems in piles for loading or segregation into products. 

shear: a device mounted on a mobile machine capable of cutting 

a tree stem at ground level using hydraulic pressure to push 

blades through the stem.

skidder: a rubber-tired or track-mounted machine designed to 

transport cut trees or processed material to a landing. Grapple 

skidders transport material by lifting one end with a grapple 

and dragging the material behind it.

Glossary of Terms

Chapter 3

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 33

Chapter 4

INTRODUCTION

Previous sections of this document deal with the production 

and harvesting of wood and associated issues, including the fuel 

properties of wood. For wood to be used for energy, it must be 

converted into other energy forms such as heat or electricity. 

This chapter covers the various types of direct combustion, 

thermochemical and biological gasification, and fast pyrolysis 

biofuel technologies for conversion of wood into useful energy 

forms. Also included is a discussion on industrial process heat, 

space heating and cooling, and electricity generation enduse applications. The latter includes expanded discussions on 

combined heat and power (CHP) systems, district heating systems, 

net metering laws, and pertinent environmental regulations.

BACKGROUND

Biomass can be used directly as a solid fuel or converted into 

gaseous, liquid, or other solid fuel forms. It can, thus, substitute for 

or supplement virtually any other energy source and is presently 

widely used in its raw form as boiler fuel in the paper industry. 

Liquid fuels are currently of particular interest because of U.S. 

dependence on imported petroleum, rising petroleum costs, and 

energy security issues associated with petroleum. Biomass is the 

only renewable source of liquid fuels that currently exists.

Three things are required for combustion to occur: (1) fuel, (2) 

oxygen, and (3) a heat source to raise the fuel above its ignition 

temperature. The rate of burning is usually controlled by limiting 

the amount of fuel present or, less often, by regulating the amount 

of combustion air present. However, insufficient combustion air 

may result in incomplete combustion, which reduces the burner 

efficiency and can cause air pollution.

As discussed in chapter 3, wood can vary widely in its physical and 

chemical characteristics. Devices that convert biomass to energy 

require certain fuel characteristics in order to process them. 

Furthermore, the energy produced or how it is eventually used 

is dependent on conversion technology. Fuel preparation must 

change the characteristics inherent in fuel into characteristics 

needed for the conversion device in a cost-effective way, while 

meeting acceptable environmental standards.

Moisture content is an important wood fuel characteristic since 

the maximum moisture content permissible for wood as a fuel 

is in the range of 65 to 68 percent.1

 Above this moisture content 

percentage, the energy required to evaporate the moisture in the 

wood is greater than the energy in the dry matter of wood, and 

combustion cannot occur unless heat is supplied from another 

source. For all systems, excessive fuel moisture can potentially 

cause corrosion and blockages of the fuel handling system and a 

reduction in combustion efficiency. Wood contains acids, and with 

sufficient moisture, can be quite corrosive.

Fuel particle size must be matched to specific burner types 

(discussed later). Stringy fuels, such as those associated with 

hardwood bark, can pose special handling problems. The presence 

of inorganic materials such as soil can increase ash content and 

change the ash’s chemical nature. Pieces of metal and oversized 

pieces of biomass can also damage equipment. 

The chemical composition of ash is important because certain 

chemicals can lower the melting point of the ash. Melted ash can 

coat the inside of boiler surfaces (referred to as slagging) and coat 

heat transfer surfaces (referred to as fouling). Certain potassium 

and sodium compounds are the primary cause of slagging and 

fouling. These chemicals, essential for plant growth, are more 

concentrated in the fastest growing plants or plant parts, such 

as leaves, twigs, and bark. In general, the stems of older trees 

have lower concentrations of these chemicals and do not cause 

problems with slagging and fouling (Baxter and others 1998).

THERMOCHEMICAL CONVERSION OF BIOMASS FUEL

Thermochemical conversion is the process of breaking down 

biomass into intermediates by using heat and then upgrading 

it to fuels through a combination of heat and pressure in the 

presence of catalysts. Several processes and systems are available 

to implement the conversion, including combustion, gasification, 

and anaerobic digestion. The processes are described below. 

Direct Combustion Processes and Systems

The three systems commonly used for direct combustion of 

biomass fuels are: (1) pile, (2) suspension, and (3) fluidized bed 

combustion (FBC). The actual type of burner selected will depend 

on variables such as amount and final form of energy needed, 

ease of permitting, and ability to handle a wide variety of fuels, 

e.g., agricultural materials, cardboard, and wood; variation in the 

amount of energy required by the end-use application; and cost of 

the system (Tennessee Valley Authority 1991). 

Chapter 4

Biomass Conversion to Energy and Fuels

Phil Badger and Pratap Pullammanappallil

1

 Kiln-dried wood used by furniture manufactures will have a moisture content of 5 to 6 percent. Freshly harvested wood typically has a moisture content of 

45 to 50 percent and is considered “green” wood. Therefore, a moisture content of 65 percent is unusually high.
Biomass Conversion to Energy and Fuels

34 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Pile combustion system—Pile combustion systems burn wood 

fuel in a heaped pile supported on a horizontal or inclined grate2

or in a thin layer spread across a grate that is either traveling or 

stationary (fig. 4.1). Air for combustion is provided under the 

grate and above the fuel pile. The spreader stokers, fuel-feed, and 

distribution systems used with “thin-pile” combustion units are 

generally quite reliable. Any problems that occur can often be 

traced to uneven fuel distribution across the grate, which results 

from either oversized fuel particles or high moisture fuel particles 

that stick together (Tennessee Valley Authority 1991). 

Pile burners are noted for their relatively simple design, low capital 

and operating costs, and ability to burn a fairly wide range of 

wood particles and moisture contents. The minimum fuel particle 

size depends on grate opening size, while maximum fuel particle 

size depends on grate design and size of the entry point into the 

combustion chamber. In general, large chunks, stringy bark, or 

sawdust-size particles may be used in these systems.

Underfeed stokers are another version of a pile burner. Underfeed 

stoker systems push fuel into the combustion chamber from 

beneath the burning pile. Usually an auger (a rotating, screwtype device) is used to push fuel into the combustion chamber. 

Particles must be small enough to flow with the auger, but not too 

fine, stringy, or green to cause packing and blockage problems. 

The optimal particle size range is dependent on auger size. 

The least complicated and least expensive of the direct 

combustion systems, the pile burners are generally used for 

smaller applications. However, when operating, they contain a 

large amount of burning fuel which prevents them from being 

shut off or slowed down quickly. Therefore, these burners are not 

compatible with energy use applications that have highly variable 

demands for energy over short periods of time. 

Suspension combustion system—As their name implies, suspension combustion systems burn their fuel in suspension. Since 

particles cannot be suspended for very long, due to the force of 

gravity, they must be relatively small (typically < one-fourth inch) 

and dry (typically < 15 percent moisture content) so they will burn 

quickly while still in suspension. (Tennessee Valley Authority 1991). 

One type of suspension burner is the cyclonic burner, which 

is in the form of a horizontal or vertical cylinder. Wood fuel is 

blown along the curve of the burn chamber and centrifugal force 

suspends the particles while they are burned (fig. 4.2). 

Hot gas Hot gas

Biomass

Biomass

Air

Air

Air

Air

Figure 4.1—Some pile combustion systems burn the wood fuel in a 

heaped pile supported on either a horizontal or inclined grate.

Figure 4.2—Example of a cyclonic burner. Wood is blown into the 

cylindrical burn chamber so that the small particles of fuel—held by 

centrifugal force—spiral around the hot walls of the burn chamber while 

they are burned. 

2

 A grate may be a flat metal plate to support the fuel while burning with holes in the plate to provide air for combustion. Another type of grate is a wide, 

moving chain across the bottom of the firebox which carries the fuel through the combustion zone.
Chapter 4

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 35

Another type of suspension system is the air spreader stoker 

system, which typically consists of a rectangular firebox with 

a stationary or traveling grate at the bottom. Wood fuel is 

horizontally injected with air into the firebox above the grate so 

that most combustion occurs with the particles in suspension. 

Unburned particles complete their combustion on the grate. 

Although suspension burners are limited in their fuel handling 

capability, these systems are more responsive to changes in heat 

demands because only a relatively small amount of fuel burns at a 

given time. 

Fluidized bed combustion system—FBC systems burn wood fuel 

on a high-temperature bed of finely divided chemically inactive 

(inert) material, such as sand, that is agitated by air blown from beneath the bed. Solid fuel is introduced into the chamber through 

an airlock, where the fuel particles burn while suspended in the 

bed (fig. 4.3). This suspension allows combustion air to reach all 

sides of the particles throughout the combustion process, making 

for highly efficient combustion. The ash produced typically consists of very small particles which are carried from the burner with 

the hot gases emitted from the burner. The hot gases pass through 

various devices to capture and control emissions (FBT 1994). 

FBC systems are particularly suited to burning a variety of fuels 

simultaneously, including those that contain high levels of ash, are 

irregularly shaped, and have high moisture content. Additionally, 

FBC systems burn the fuel as soon as it is introduced into the 

burner. This makes FBC systems highly responsive to rapid 

changes in heat demand. They are also easy to maintain since 

the combustion chamber does not contain grates that must be 

cleaned, repaired, and replaced. 

On the downside, these systems are relatively complex and have 

initial costs that are approximately 10 percent higher than grate 

systems. Also, fuel size is important to effective operation of these 

systems. Small particles can pass through the unit and may not be 

caught by the cyclone3

 for recycling back to the bed. Excessively 

large particles can be too heavy to float in the fluidized bed and 

may cause problems. 

Fuel and bed material are fed into the FBC using under-bed, 

in-bed, or over-bed feed systems. All of these systems need a 

pressure seal to force fuel into the FBC and resist backpressure 

from the bed. A rotary airlock (a paddle wheel turned by a motor 

to allow particles to pass through it but minimize airflow) is often 

used for the pressure seal. This type of pressure seal requires 

fairly uniform particles, and the size of the airlock determines the 

maximum particle dimensions. The fuel must also be dried so 

that it will not stick to the conveyors and other parts of the 

handling system.

Figure 4.3—Example of a fluidized bed combustion (FBC) unit. In the upper 

left picture, the system is shut down. In the upper right picture, air is being 

injected beneath the bed to agitate it. In the lower left picture, fuel is being 

fed into the bed while the bed is being agitated with air. And in the lower 

right picture, an absorbent material, such as limestone, is being fed into the 

bed to absorb sulfur and other pollutants, and ash is shown being removed. 

3

 A cyclone is a device that uses centrifugal force to remove particles from a rapidly moving airstream. The upper half of the cyclone is a vertical cylinder 

and the lower half is in the form of a downward pointing cone. The air containing the particles is injected at high speed into the cyclone near the top of the 

vertical cylinder and along the tangent of the cylinder. The particles in the air are forced out to the cylinder wall by centrifugal force where they slide down 

into the cone and out the bottom of the cyclone. Clean air exits out of the top center of the cyclone.

An estimated 2,000 wood-fired, industrial, or commercial wood-energy systems are in use in the 

Southeastern United States. In general, all of the previously 

listed types of burners are found in the region. The most 

common is the grate-type boiler, which generates steam. 

A distant second place is hot water boilers, followed by 

hot air systems and thermal fluid (hot oil) heat transfer 

systems. Grate burner systems are much more common 

than suspension burner and fluidized bed systems. 

Outside of the paper industry, which accounts for an 

estimated 75 percent of the industrial wood fuel use in 

the Southeast, most of the wood-fired boilers are used for 

industrial process heat in the rest of the forest products 

industry. A small percentage is used by nonforest products 

industries and commercial entities for process heat (heat 

used by industries in their manufacturing processes) and 

heating and cooling. A still slightly smaller percentage 

is used for heating and cooling schools, prisons, and 

hospitals, primarily in Georgia and Missouri. 
Biomass Conversion to Energy and Fuels

36 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Under-bed feed systems usually convey fuel in an airstream within 

a pipe (pneumatic conveyance), and are more complex than the 

other types of fuel feed systems. Sizing and drying the fuel are 

necessary to prevent handling system blockage. 

In-bed feed systems are similar to the under-bed feed systems, 

particularly if fuel is conveyed pneumatically. More complex than 

over-bed systems, they are generally used for burning highmoisture fuels such as slurries.

Over-bed feed systems include conventional spreader feeders, air 

swept feeders/mills, and gravity feeders. Less prone to blockages, 

these systems are simpler to construct and maintain. Since the fuel 

entry point is above the pressurized bed, there is less pressure on 

the airlock, reducing the performance requirements of the airlock. 

For these reasons, over-bed feed systems are most commonly 

used to feed woody fuels into FBCs. 

Gasification Processes

Thermochemical processes, e.g., direct combustion, gasification, 

and pyrolysis, use heat to cause chemical reactions. If the thermochemical process occurs at high temperature, it is termed a 

pyrolysis process. 

Upon heating, biomass materials decompose into a number of 

gases and vapors and char. If heated to high enough temperatures 

in the presence of air, biomass materials will combust. If the 

biomass is heated in an enclosed container in the absence of air, 

the gas, vapor, and char cannot burn and can be recovered as 

products (Klass 1998).

The most common example of a thermochemical process is a direct 

combustion process, such as a campfire burning wood. The key to 

understanding the nature of thermochemical processes starts with 

the direct combustion process. All other thermochemical processes 

can be thought of as direct combustion processes that have been 

modified to obtain another desired outcome. The key variables for 

any thermochemical process are heating rate, final temperature, 

oxygen levels, pressure, and reaction time. Other important factors 

include particle size, moisture content, design of the container for 

the process, biomass chemical composition, and amount and type 

of ash associated with the material (Georgia Tech 1984). 

Decomposition of biomass using thermochemical processes 

involves a complex reaction system that generates gases, liquids, 

and solids. Initially, in the direct combustion process, which goes 

through several distinct stages, heat must be added to biomass 

material until it reaches its ignition temperature. At that point, it 

will continue to burn as long as sufficient oxygen is present and 

the temperature remains at or above the ignition point (Georgia 

Tech 1984). To summarize, direct combustion consists of the 

following main steps:

• Drying of biomass material

• Raising the temperature of the material to its ignition point, 

accompanied by decomposition of the material into gases 

and vapors

• Further decomposition and evolution of volatiles and gases 

leaving a char; and 

• Combustion of the char, leaving an ash residue

As described in the direct combustion process, gases and 

vapors are given off at certain points of a thermochemical direct 

combustion process. One way to thermochemically gasify biomass 

is to heat it in an enclosed container while allowing a small 

amount of oxygen to enter. The oxygen allows some combustion 

to occur, which provides the heat necessary to cause the biomass 

to decompose into gas, vapor, and char. However, by limiting the 

amount of oxygen in the container, there is not enough oxygen 

present to allow the remaining gas and vapor to burn, so these 

products can be recovered. Because the amount of oxygen is 

limited, temperature of the gasification process is typically lower 

than in direct combustion. 

The gas and vapor generated can be piped to a boiler or 

combustion device where it is mixed with oxygen and burned in 

a manner similar to burning natural gas. The amount of energy in 

the gas is roughly 150 British thermal units (Btus) per cubic foot. In 

contrast, natural gas has about 1,000 Btus per cubic foot (Georgia 

Tech 1984). 

Another way to thermochemically gasify biomass is to place it in 

an enclosed container without any oxygen and heat the container 

from outside. Since there is no partial combustion, the amount 

of gas and vapor recovered is higher than with the previously 

described system. The amount of energy in the gas from these 

systems can be as high as 500 Btus per cubic foot (FBT 1994). 

A similar process can be used to make charcoal. In one charcoal 

production method, a pile of wood is placed in an enclosed 

container and ignited. Then the amount of oxygen is restricted 

so that the wood can only burn slowly. The wood is allowed to 

smolder for a period of time before all oxygen is cutoff, which 

eventually causes the fire to go out. The heating process drives 

most of the gases and vapors out of the wood leaving relatively 

pure carbon, or charcoal, in its place. A process optimized to 

produce charcoal would be a slow pyrolysis process and, in 

comparison to combustion, would operate at relatively low 

temperatures and take a few hours or days to complete (Georgia 

Tech 1984). 

Most gasifiers are designed so that the biomass is placed inside a 

container. For these gasifiers to work properly, biomass particles 

must be large enough for heat to reach them inside the container 

and provide a path for the gases and vapors to flow out. Another 

type of gasifier is the fluidized bed gasifier which operates 

similarly to a fluidized bed combustor (previously described, see 

fig. 4.3 and accompanying text), except that oxygen is limited 

inside the container where gasification occurs (FBT 1994). 
Chapter 4

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 37

Biomass gasifiers were widely used to provide fuel for vehicles in 

Europe and Asia during World War II when petroleum was scarce. 

These gasifiers were either mounted on the vehicle or on a trailer 

pulled behind the vehicle (Bridgewater and others 1999). 

One way to generate liquid fuels from biomass is through a fast 

pyrolysis process. A fast pyrolysis process is a gasification process 

optimized to produce vapor. This is accomplished by rapidly heating 

the biomass to temperatures between 750 and 1,000 °F within a 

few seconds and then cooling and condensing the vapors within 2 

seconds to recover a liquid. When made from wood, the resulting 

liquid has an energy content of around 80,000 Btus per gallon, 

roughly the same as ethanol. The liquid product looks similar to 

motor oil and is called pyrolysis oil or bio-oil (Bridgewater and 

others 2002). By performing basically the same process under high 

pressure (a liquefaction process), the liquid product can have an 

energy content similar to diesel fuel, about 139,000 Btus per gallon. 

Fast pyrolysis processes have several distinct advantages. One is 

that biomass can be processed into bio-oil at one location and 

then used at another location in a manner similar to how fuel oil is 

used. In contrast, a direct combustion or gasification system must 

be located adjacent to where energy is needed. Thus, biomass 

must be hauled to the gasifier or direct combustion unit, which is 

expensive, because biomass is relatively light weight.4 The gases 

and, if necessary, the char generated by the fast pyrolysis process 

can provide thermal energy for the process. These features allow 

bio-oil to be produced in satellite plants and used in a centralized 

energy conversion facility; or allow for operation of a central 

bio-oil production facility in conjunction with distributed energy 

conversion systems. Thus, bio-oils offer greater flexibility than solid 

or gaseous fuels (Badger and Fransham 2003). 

Anaerobic Digestion

Anaerobic digestion (or biogasification) systems use microorganisms to break down organic materials under oxygen-free 

(anaerobic) conditions to produce a biogas. The process occurs in 

natural environments, and when it is made to occur in engineered 

environments, it is called anaerobic digestion (digestion since the 

organic matter is eaten and digested by the micro-organisms). 

Anaerobic digestion processes—Anaerobic digestion takes 

place in two stages as certain micro-organisms feed on organic 

materials. First, acid-producing bacteria break the complex organic molecules down into simpler sugars, alcohol, glycerol, and 

peptides. When these substances have accumulated in sufficient 

quantities, a second group of bacteria convert some of the simpler 

molecules into methane (Klass 1998). 

Like all living things, micro-organisms require environmental 

conditions that are conducive to their survival and growth. In 

this case, methane-generating micro-organisms are especially 

sensitive to environmental conditions. Temperature, acidity (pH), 

residence time, and amount of water are important environmental 

conditions for these micro-organisms. For most types of methane 

digesters, enough water must be present to form a slurry; thus, 

anaerobic digestions are well suited for treatment of wastewater 

or slurries high in organic matter. Conversely, anaerobic digestion 

systems are not well suited for processing dry biomass materials 

because a large amount of water must be added at the beginning 

of the process and then discarded at the end of the process 

(Chynoweth and Jerger 1985). 

Anaerobic digestion processes can take hours or days while the 

microbes grow and reproduce. Therefore, anaerobic digestion 

processes are slower than thermochemical processes, which can 

occur in seconds. The biogas typically contains from 50 to 70 

percent methane (the main ingredient of natural gas) and has a 

corresponding energy content of 500 to 700 Btus per cubic foot. 

The rest of the biogas is typically 30 to 50 percent carbon dioxide, 

plus small amounts of other gases. Biogas will burn cleanly and 

can substitute for natural gas in most applications (Chynoweth 

and others 1991). 

There are two main families of micro-organisms in most anaerobic 

digestion systems. One family likes to have temperatures at 95 to 

105 °F and is called a mesophilic system. Another family operates 

at 125 to 135 °F and is called a thermophilic system. Systems that 

operate at higher temperatures have the advantage of faster 

digestion processes. Therefore, the tanks and containers used 

in these systems can be smaller. However, higher temperature 

systems have the disadvantage of requiring an outside heat source. 

The digestibility of an organic material is measured in terms of 

the material’s volatile solids5

 (VS) content. This material is the 

part that microbes can literally eat and digest. For this discussion, 

the focus is on the applicability of anaerobic digestion to woody 

materials, which are also considered a ligno-cellulosic material. 

Ligno-cellulose materials are primarily composed of cellulose, 

hemicellulose, and lignin. The percentage of these constituents 

depends on the species, age, and growth conditions of the wood. 

Typically, the relative quantities are 40 to 45 percent cellulose, 

20 to 30 percent hemicellulose, and 20 to 30 percent lignin. Even 

though cellulose and hemicellulose can be anaerobically digested, 

these materials are relatively difficult to digest since the sugars 

present must first be broken down. Additionally, lignin encases 

the cellulose and hemicellulose, making it difficult for microbes to 

reach them (Jerger and others 1982). 

4

 Depending on species, a solid block of dry wood will have from 25 to 54 pounds of material in a cubic foot. Chipped green wood has roughly 22 pounds of 

material in a cubic foot. Dry wood shavings may only have 5 to 6 pounds of material per cubic foot. Thus, trucks hauling biomass may be limited by volume 

instead of weight. Since wood for energy is usually sold by weight, the relatively low amount of weight that can be transported due to volume limitations 

can make hauling wood expensive.

5

 Volatile solids (VS): Those solids in water or other liquids that are lost on ignition of the dry solids at 550 oC (http://en.mini.hu/environment/liquid.html).
Biomass Conversion to Energy and Fuels

38 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

However, cellulose and hemicellulose components of woody 

biomass can be converted to methane by anaerobic digestion 

without pretreatment other than particle size reduction, e.g., 

grinding (Chynoweth and Jerger 1985, Jerger and others 1982). 

This is accomplished by utilizing special digester designs that 

provide good conditions for micro-organisms that work better 

with woody materials. 

Advantages of anaerobic digestion over thermal gasification 

include:

• Higher moisture content that does not result in reduced 

efficiency

• Biogas that is a mixture of relatively few gases and that has a 

higher heating value

• No requirement for oxygen to make medium- or high-energy gas

• A process that can be carried out at ambient pressures and 

temperatures, and 

• An economic process at a variety of scales

Methane yields for various woody biomasses are listed in table 

4.1. For hardwoods, yields typically range from 3.37 to 6.58 cubic 

feet of methane per pound of VS. For softwoods like Eucalyptus

spp. and Pinus taeda (loblolly pine), yields range from 0.16 to 0.96 

cubic feet of methane per pound of VS (Turick and others 1991). 

Anaerobic digester systems—There are several different types 

of anaerobic digesters. However, only two types, slurry and 

high-solids (or dry) digesters, will be discussed here because 

these two types are most suitable for anaerobically digesting 

wood. Slurry digesters usually operate with slurries that have 

over 90 percent water and a few percent solids. High-solids or 

dry digester designs minimize the use of water. Both designs can 

be used for woody biomass feedstocks and can be operated in a 

continuous, semicontinuous, or batch mode. Each digester type 

has advantages and disadvantages, which change based on the 

material being digested. Because some digester systems work 

much better with woody materials than others, not all digester 

designs will be discussed here. 

Slurry digesters stir the slurry inside the digester to keep solid 

particles mixed in the liquid. These designs are operated at a 

solids content of 4 to 20 percent, and their benefits include ease 

of feeding and operation and easy removal of digested effluent. 

Such designs are commonly used for sewage sludge digestion. 

For woody biomass, which requires the addition of water to make 

slurry, this type of design is less efficient than the high-solids type 

(Chynoweth and Jerger 1982). 

Anaerobic digestion with minimal water addition allows digestion 

of a higher percentage of solids, making smaller digesters as 

efficient as larger digesters. High-solids or dry anaerobic digesters 

are typically operated at a solids content of 35 percent. For woody 

biomass, the performance of dry digesters, like nonmixed vertical 

flow and two-stage leach-bed packed-bed reactor systems, is 

superior to slurry digesters. Anaerobic digestion of green waste 

collected from a municipal solid waste disposal facility produced 

methane yields of 3.05 and 4.49 cubic feet per pound of VS, 

respectively, in continuously fed stirred tank anaerobic digesters 

Table 4.1—Methane yield of various woody biomass types and comparison to methane 

yield from cellulose powder 

Common name Scientific name Methane yield

ft3 per pound of volatile solids

Cellulose powder 6.26

Pussy willow Salix eriocephala 4.66

Shining willow S. lucida 4.33

Coyote willow S. exigua 4.49

Common osier S. viminalis 5.46

White willow S. alba 4.82

Purpleosier willow S. purpurea (SP3) 3.69

Peachleaf willow S. amygdaloides (SAM5) 3.37

Halberd willow S. hastata (SH2) 3.69

Hybrid poplar Populus nigra x P. maximowiczii 6.26

Hybrid poplar P. x euramericana 6.58

Eastern cottonwood P. deltoides 4.82

American sycamore Platanus occidentalis 6.10

Black locust Robinia pseudoacacia 4.82

Sweetgum Liquidambar styraciflua 4.17

Source: Turick and others (1991). 
Chapter 4

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 39

and nonmixed vertical flow reactors operated at a loading rate 

of 0.1 pound VS per cubic foot per day at mesophilic (100 °F) 

temperatures (Chynoweth and others 1991). For the same biomass 

feedstock, at the same loading rate and temperature, a leach-bed 

packed-bed system produced a methane yield of 5.14 cubic feet 

per pound of VS. 

A schematic diagram of an unmixed vertical flow digester is 

shown in figure 4.4. This process can be operated continuously 

or semicontinuously. It is a plug flow design wherein the biomass 

flows from the top of the reactor, where it is fed, to the bottom, 

without undergoing any mixing. Biomass is digested as it 

moves down, releasing biogas bubbles that rise to the top. The 

undigested residue is removed from the bottom of the reactor, 

and part of it is recycled and mixed back with the feed. The rest 

is dewatered and disposed of. Leachate6

 from water removal 

operations is also recycled and mixed with incoming biomass. 

Mixing undigested residue and leachate with the new material 

entering the digester provides the new material with microorganisms for digestion, nutrients for microbial growth, and 

optimal moisture for the microbes, while also helping to keep the 

slurry from becoming too acidic (Chynoweth and others 1991).

A leach-bed packed-bed configuration is shown in figure 4.5. 

This is a batch process and requires two reactors, one containing 

a bed of fresh biomass that is to be digested and the other 

containing anaerobically digested residue. Water is added to the 

feedstock (reactor 1) in excess of saturation capacity to moisten it 

and produce leachate that collects at the bottom of the bed. This 

leachate is flushed through the stabilized residue (reactor 2) and 

leachate from the stabilized residue (reactor 2) is flushed to the 

top of the fresh bed of biomass (reactor 1). 

This leachate exchange strategy provides numerous benefits to 

initiation of anaerobic digestion in the fresh biomass. Initially, 

fermentation reactions that produce volatile organic acids are 

started in the bed of fresh biomass. Water flushed through the bed 

leaches out these organic acids, which are then flushed through 

Biomass feed Biogas

Recycled part of

digested residue

and leachate

Digested residue

Figure 4.4—A schematic diagram of an unmixed vertical flow digester. In 

operation, wet biomass continuously flows into the top of the digester and 

slowly settles to the bottom while microbes digest the biomass. The biogas 

bubbles to the top of the digester where the gas is collected and piped 

to where it can be used. Undigested residue is removed from the bottom 

of the digester and part of the residue is recycled back to the top of the 

digester to seed the incoming biomass with microbes.

6

 A leachate is a liquid that collects at the bottom of the reactor. It can usually contain both dissolved and suspended material.

Biomass feed

Water

Fresh

biomass

leach-bed

Stabilized

residue

packed-bed

Biogas

Residue

Residue

Leachate Leachate

Reactor 1 Reactor 2

Figure 4.5—A leach-bed packed-bed biogasification system. In operation, 

biomass is placed into the digester in a batch. The second container 

contains mostly water and some previously digested biomass. A water/

biomass mixture from the second digester is slowly circulated through the 

bed of fresh biomass in the first reactor to seed the biomass with microbes 

and cause digestion to occur. The resulting biogas product bubbles to the 

top of the digester where the gas is collected and piped to its end-use 

point. After biogas production stops, the spent residue is removed from the 

digester and the process repeated with a new batch.
Biomass Conversion to Energy and Fuels

40 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

the stabilized residue. The stabilized residue, having already 

undergone anaerobic digestion, contains the methane-generating 

microbes that consume the volatile organic acids from the fresh 

bed of biomass. Some of these methane-generating microbial 

populations are also flushed out with the leachate, which serves 

to inoculate the bed of fresh biomass. In addition to providing 

seed microbes, this leachate exchange strategy provides nutrients 

and a pH buffer to the fresh biomass to help sustain the microbial 

populations. Once this reseeding has been initiated in the fresh 

bed, leachate is only recirculated to keep the bed moist. The 

spent and now stabilized residue can either be disposed of or 

used to initiate methane generation in another batch of biomass 

(Chynoweth and others 1991). 

WOODY BIOMASS END USES AND 

POWER GENERATION

For the solar energy stored in wood to be of practical use, it must 

be converted into a more useful form of energy. The near-term 

uses of wood for energy include industrial process heat, heating 

and cooling buildings, and electrical power generation. Most 

wood is burned, but some is converted to gas and burned to 

produce steam, hot water, hot air, or hot oil that can be used to 

carry and distribute the heat to other locations. 

Boilers, to generate steam or hot water, consist of an enclosed tank 

with tubes that pass through one wall of the tank and out another 

side of the tank. In firetube boilers, the hot air and gases from 

combustion (stack gases) pass through the tubes of the boiler, 

and the water is contained in the surrounding tank. Watertube 

boilers are the opposite, with water flowing through the tubes 

and the hot stack gases on the outside of the tubes. Firetube 

boilers are less expensive to make and can be used in low-pressure 

steam applications. Watertube boilers are more expensive to 

manufacture because they use many small-diameter tubes, which 

are required for higher steam pressures (Georgia Tech 1984). 

Because boilers generate steam at relatively high pressure,7

 their 

use is closely regulated, and they are more costly to construct 

and operate than other systems. Hot water systems do not carry 

as much energy per pound of water as steam systems; therefore, 

larger amounts of heat transfer surfaces are required when using 

hot water systems. However, hot water systems are less expensive 

to build and operate than steam systems because they can 

operate with little or no pressure. Hot air systems are only used 

when the heat does not have to be transferred very far, such as in 

heating a commercial or residential building or lumber dry kiln 

(Georgia Tech 1984). 

Hot oil systems combine the best aspects of steam and hot water 

systems and are competitive with steam systems in capital cost 

and less expensive to operate. Some hot oils (also called heat 

transfer fluids) can be heated to over 600 °F without pressurizing 

the system. Thus, hot oil systems can reach the temperatures that 

steam systems reach without using elevated pressures. Oil systems 

do not require a boiler operating license or water treatment 

system (since they do not use water), and they do not create 

freezeup problems. 8

Industrial processes use heat in a variety of ways, including paint 

drying, cooking, sterilizing, pasteurizing food, setting dyes in cloth, 

and melting metals. Using energy to heat and cool buildings (also 

called space heating and cooling) is similar to using it for industrial 

processes, except that, in the case of energy use for a building, energy 

is transferred to a heat exchanger in the building being heated. 

Cooling With Wood

Energy from wood can also be used to cool buildings. One method 

is to use wood to generate electricity that powers a conventional 

electrically powered air conditioning system (compression 

cycle). Another method is to replace the electric motor on the air 

conditioner’s compressor with a steam turbine. A more common 

method is to use low-pressure steam to activate absorption 

chillers. Early refrigerators in the United States operated on natural 

gas to provide a source of heat that activated an absorption 

system. Absorption systems were later replaced by the more 

efficient compression cycle systems that still are commonly part of 

the modern refrigerator. However, the absorption system has the 

major advantage of using low-temperature waste heat, including 

low-pressure steam. Absorption systems are still widely used in the 

United States in CHP applications (Wiltsee 1994, Guinn 1992). 

7

 Utility boilers typically operate at high-steam pressures and high-steam temperatures. Steam with a gauge pressure of 2,000 pounds per square inch will 

have a temperature of 1,000 oF.

8

 Personal communication. 2006. David Gamble. President. Green Energy Technologies, P.O. Box 159, Moody, AL 35133. 

A common mistake made by engineers unfamiliar with wood-fired systems is to design the system so that it 

is normally operating in the middle instead of the upper 

end of its operating range. Unlike most fossil fuel-fired 

systems, the efficiency of wood-fired systems typically falls 

off rapidly below the upper end of its operating range. 

Fossil-fueled systems are frequently oversized to make sure 

that they meet their performance requirements; however, 

their efficiency stays relatively constant in the upper end of 

their operating range so that their system efficiency is not 

significantly hurt.
Chapter 4

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 41

Although many people have tried to develop cost-effective woodfired cooling systems for residential and commercial applications, 

the development of such systems has not been successful. Usually, 

industrial wood-fueled cooling systems can be cost effective only 

if large quantities of waste heat are available at temperatures 

sufficient to operate absorption chillers. Nevertheless, industrial 

chillers based on absorption systems are more commonly used 

today than most people realize (Wiltsee 1994). For a good example 

of an industrial success story, see text box below for a discussion 

of the CHP heating and cooling system used in La-Z-Boy®

 Furniture 

manufacturing plants (SERBEP 1997). 9 

District Heating Systems

District heating systems use one or more central plants, e.g., a 

boiler, and distribute heat via pipes to two or more buildings 

to supply space heat or hot water for domestic use. Sometimes 

district heating systems are used to provide process heat to 

industrial users either in combination with residential, commercial, 

or institutional users, or with a district heating system to serve a 

specific industrial park. 

Central systems reduce capital and operating costs because they 

reduce the number of plants and the number of crews required 

for staffing the plants, and they are more efficient than smaller 

plants. Capital costs are reduced even though additional piping 

is required between the plant and the various buildings where 

heat is used. Air quality is improved since it is easier and more cost 

effective to put pollution control equipment on a central plant 

than on many small dispersed plants (Maker and Penny 1999). 

District heating systems are frequently used on college campuses 

and State institutions where several buildings are close together 

and under the control of one authority. In northern climates, 

district heating systems frequently serve entire towns, apartment 

complexes, villages, or parts of large cities. For example, large 

wood-fired district heating systems commonly serve entire 

communities in Scandinavia. In 1999, Finland and Denmark 

supplied 50 percent of their respective space heating needs with 

district heating systems, while Sweden provided 3 percent (Maker 

and Penny 1999). 

District heating systems offer several advantages for both the 

customer and the community. Customers do not have to own 

and operate their own heating systems or procure and store fuel 

onsite. The central plants are operated around the clock by trained 

professionals, and the systems have backup boilers and standby 

power generators in case of power outages. For these and other 

reasons, district heating systems historically have had a high level 

of reliability.

Since 1983, downtown St. Paul, MN, has been served 

by a hot water district heating system that originally 

burned coal, oil, and natural gas. In 2001, on the same site, 

District Energy of St. Paul opened a companion woodfired CHP system equipped with a 25-MWe backpressure 

turbine. The plant uses 275,000 tons per year of municipal 

tree trimmings and clean wood wastes, and provides 

heating, cooling, and electricity to 141 large buildings and 

298 single-family residences through 15 miles of pipe. The 

system heats over 23 million square feet of floor space, or 

about 75 percent of the city’s downtown area. 

La-Z-Boy® Furniture Company, a major manufacturer of upholstered furniture, uses wood waste-fueled CHP 

systems in all of its furniture manufacturing plants. The 

company purchases green lumber from sawmills, and kiln 

dries the wood onsite. The wood, roughly 90 percent soft 

maple (Acer spp.), is processed for frame components, 

and all the sawdust and wood scraps are conveyed 

pneumatically to silos for storage. This approach has been 

in place since the company’s first wood-fired boiler was 

installed in 1974 at its Dayton, TN, facility.

The original boiler system has been upgraded to improve 

controls and efficiencies, and to increase capacities due 

to plant expansions. The current system now consists of 

a wood-fired boiler system [30,000 lbm steam at 300 psi) 

and two 350-kW backpressure turbines. Heat is used for 

dry kilns, for heating 900,000 square feet of floor space, 

for air conditioning, and for generating electricity. When 

building heat is required, steam from the backpressure 

turbines heats water that circulates through the plant 

to unit heaters. If cooling is required, the steam from the 

backpressure turbines is sent to an absorption chiller, 

which chills water in the same circulation loop used for 

heating. When mornings are chilly and afternoons hot in 

the spring and fall, the same system is used for heating 

in the morning and cooling in the afternoon. The CHP 

system saves the company on electricity costs, eliminates 

landfilling of 10,000 tons per year of wood waste, and 

improves working conditions for plant employees. 

9

 Additional information on cooling with wood is available in “Heat-Activated Cooling Devices: A Guidebook for General Audiences” and “Design Guide for 

Thermally Activated Air Conditioning”. The publications are available from General* Bioenergy at www.bioenergyupdate.com.
Biomass Conversion to Energy and Fuels

42 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

District heating systems that are constructed to be fuel-flexible 

can provide more stable heating costs than those strictly using 

fossil fuels. This is especially true of systems designed to use 

biomass fuels. Frequently, district heating systems can obtain 

low-cost waste heat from industrial processes or utility plants. 

Many communities view the relatively inexpensive energy that 

comes from district heating systems as an incentive to draw new 

businesses. Some communities even have set up entire industrial 

parks around district energy systems (Maker and Penny 1999).

Electric Power Production

Typically, electricity-generating plants generate steam with 

boilers, from which power is generated by passing the steam 

through steam turbines, as shown in figure 4.6. This process 

is also known as a Rankine cycle. The amount of electricity 

generated is directly proportional to the flow rate of steam and 

the drop in steam pressure as the steam flows through the turbine 

and releases its energy. Thus, to maximize power production, the 

pressure drop must be maximized. 

The efficiency of steam turbines is low for very small turbines. 

Larger turbines are more efficient, partly because they can use 

multistage turbines that pass the steam sequentially through 

several sets of turbine blades to maximize energy extraction 

(Wiltsee 1993). 

Under the best scenario, only about one-third of the energy in the 

fuel that goes into the boiler comes out as electrical energy. The 

rest of the energy is in the form of low-temperature steam, hot 

water, or hot air. Although the quantities of waste heat generated 

by a power plant may be quite large, the usefulness of this heat 

is limited by its low temperature. This is because the transfer of 

heat requires a temperature difference, with larger temperature 

differences providing more efficient heat transfer. Waste heat 

discharged from coal-fired power plants is typically in the range of 

70 to 90 °F, which limits the applications for which the heat may be 

used (Hubert and Madewell 1987). 

CHP or cogeneration plants recover some of the heat from power 

generation for useful purposes. One way heat is recovered is 

with a backpressure turbine. Backpressure turbines do not have 

a condenser on their steam exit but instead regulate steam flow 

Steam

Boiler

Pump

Condensate

Condenser

Generator

Figure 4.6—A diagram of a condensing steam turbine system. Steam 

from the boiler is passed through a steam turbine which powers a 

generator to generate electricity. A condenser on the steam outlet port 

of the turbine condenses any remaining steam back into a liquid so 

that it can be pumped back into the boiler to repeat the cycle. Since 

4,000 cubic inches of steam will condense into one cubic inch of water, 

condensing the spent steam also creates a vacuum at the port of the 

turbine. And since the efficiency of the turbine depends on the flow 

rate of steam and the pressure drop of the steam as it flows through the 

turbine, the act of condensing the steam also increases the efficiency 

of the electricity generation process. However, the act of condensing 

the steam requires dumping a large amount of heat in the form of hot 

air or hot water. This water or air is usually at such a low temperature 

that it has little or no value and consequently, the energy is lost. A large 

amount of energy is required to inject spent steam from the turbine—

which is at a relatively low pressure when it exits the turbine—back 

into the boiler. Therefore, in order to maximize electrical production, 

the steam is condensed into a liquid which can be much more cost 

effectively injected back into the boiler. In addition, condensing the 

steam creates a vacuum, which further increases the pressure drop 

across the turbine and increases generating efficiency. 

As a rule of thumb, 1 dry ton per hour or 2 green tons per hour of wood fuel can generate 1 MW of 

electricity. In the strictest sense, a dry ton of wood contains 

no moisture. However, in practice, a dry ton of wood 

frequently refers to wood that has a moisture content of 10 

percent or less. A green ton of wood contains > 10 percent 

water and usually refers to wood containing 40 to 50 

percent water, a moisture content typical for wood freshly 

harvested in the summer. 

I

n general, at least 100-psig steam pressure is required 

for steam flow sufficient to operate a steam turbine. 

Some turbines may require even higher pressures. It is 

a common mistake to install a steam boiler with the 

intention of generating electricity in the future and later 

discovering that the boiler does not have sufficient pressure 

for power generation. 
Chapter 4

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 43

to provide low-pressure steam, e.g., 15 pounds per square inch, 

from the turbine (fig. 4.7) (Guinn 1990). Steam at level pressure 

has enough energy to be useful and also enough pressure 

to move the steam to its intended point of use. However, the 

amount of electricity that can be generated is reduced because 

the pressure drop across the turbine has been decreased. 

Although the amount of electricity production has decreased, 

the overall system efficiency has increased due to the capture 

and use of heat that was formerly wasted. This concept is 

illustrated in figure 4.8.

Another way to recover useful steam from a steam turbine 

is through an extraction turbine (fig. 4.9). An extraction 

turbine operates like a condensing turbine except that 

steam is extracted at a point as it flows across the turbine 

instead of being recovered as it exits the turbine. The point of 

extraction depends on how much steam pressure is required. 

Extraction turbines can be designed to match the steam 

flow and pressures required for a specific application, thus, 

better matching steam flow to heat demand for the enduse application. It is not possible to maximize both heat and 

electricity generation—one is always at the expense of the 

other. As a rule, it is best to maximize the most valuable energy 

in a CHP system, which is usually electricity (Guinn 1990). 

CHP applications work best when there is a year-round steady 

demand for both electricity and heat. Certain industries, e.g., 

Figure 4.8—An example of a CHP system for an ethanol plant. In this example the industrial facility needs 

30 units of electricity and 45 units of steam. The facility can purchase the electricity from the local power 

company, where the power company uses 98 units of fuel to generate 30 units of electricity at 31 percent 

efficiency. The company could also install a boiler (or purchase steam from another source) to provide 45 

units of steam, which requires 56 units of fuel at 80 percent efficiency. Alternatively, the company could 

install a CHP system at the facility which would provide the same 30 units of electricity and 45 units of 

steam. The CHP system would only require 100 units of fuel (versus the 154 units required by separate 

sources of steam and electricity) and would have an overall system efficiency of 75 percent. In addition, the 

self-generation of power can provide less variation in the voltage fluctuations over grid supplied power and, 

depending on how the system is designed, a means of standby power. 

Boiler

Pump

Generator

Dry 

kiln

Steam

Steam

Condensate

Figure 4.7—A diagram of a backpressure (noncondensing) steam turbine 

system. Steam from the boiler is passed through a steam turbine which 

powers a generator to generate electricity. However, the system is designed 

so that the steam exiting the turbine still has some pressure left (typically 

15 psi). The low pressure provides the energy to move the steam through 

a pipeline to a point where the steam can be used and, in the process, 

condensed back to a liquid. Forest product industries frequently will use 

these systems to generate electricity and heat dry kilns to dry lumber. 

Since the efficiency of the turbine depends on the flow rate of steam 

and the pressure drop of the steam as it flows through the turbine, the 

decrease in pressure drop across the turbine also decreases the efficiency 

of the electricity generation process. However, more of the overall energy 

is recovered from this type of process, so that the backpressure turbine is 

more cost effective. 
Biomass Conversion to Energy and Fuels

44 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

forest operations that require kilns for drying lumber, and certain 

institutions, e.g., hospitals, prisons, and colleges, are particularly 

good candidates for CHP systems. 

Determining a cost-effective, minimum-size, wood-fired, steamturbine, electricity-generating system is not easy, as it depends 

on several factors. However, in certain conditions, wood-fired 

boilers around 600 boiler horsepower and that generate 300 to 

1000 kW of electricity in CHP applications may be cost effective 

(Easterly and Lowenstein 1986). Typically, to be cost effective, the 

boilers must produce electricity that is valued at retail electricity 

purchases, and that generates significant revenue from its thermal 

energy. If one were also paying to get rid of wood residues, the 

inhouse use of these residues for electricity generation would 

improve the cost effectiveness of CHP systems (Wiltsee 1993). 

Types of generators—There are two basic types of electricity 

generators: the induction generator and synchronous generator. 

Generators require a magnetic field to generate electricity. An 

induction generator uses electricity from the grid to create the 

magnetic field of the generator. Therefore, an induction generator 

cannot operate if it cannot receive electricity from the utility grid. 

Induction generators are, therefore, useless for standby power 

generation. Their significant advantages are low cost, simplicity, 

and reliability. 

Synchronous generators are more complex because they are 

designed to operate on or off the grid. However, they require 

complex controls to match their electrical output to that of the 

grid. Synchronous generators are, thus, more costly to install 

and operate. Utility power plants use synchronous generators 

exclusively (Guinn 1990). 

Independent power plants—Independent power plants are 

electricity-generating plants that operate outside of a regulated 

utility business structure and sell power to a utility. The 45-MW 

wood-fired plant at New Bern, NC, and the 45-MW wood, landfillgas, and tire-crumb plant in Lakeland, FL, are two examples. 

Typically, these plants use stoker-fired steam boilers and turbines. 

Cofiring—Some boilers can burn wood fuel in a process called 

cofiring that burns wood and coal simultaneously in the same 

boiler. As discussed previously, types of burners for wood vary 

according to the form of fuel, the size of installation, and other 

factors. Boilers that use spreader stokers can cofire wood and coal 

together on a grate, providing that the wood and coal particles 

are large enough not to fall through the grate. Because of the 

difference in bulk density and other characteristics governing the 

handling of each fuel, wood and coal are typically stored and fed 

separately to the spreader stoker. The main boiler on the campus 

of the University of Missouri is an example of such a system (Foster 

Wheeler 1997).

Large utility plants typically pulverize coal to a talcum powder 

consistency and then burn it in suspension. The use of small 

particles and complete exposure of the particles to air allows the 

particles to burn quickly and efficiently, as required for suspension 

burn systems (Foster Wheeler 1997). 

There are two methods of feeding wood fuels into coal plants for 

purposes of cofiring, each with its advantages and disadvantages. 

One method is to process the wood through the coal handling 

equipment and feed wood and coal together (commingled) into 

the plant. While the easiest and lowest cost method, it also has 

the disadvantage of limitations on the amount of wood that 

can be used (typically, no more than 7 percent of the boiler’s 

gross energy input but for some boilers, no more than 4 percent) 

(Foster Wheeler 1997). This limitation stems from the small woodhandling capacity of pulverizers (wood is fibrous and difficult 

to pulverize), as well as from difficulties inherent in conveying 

the mixture of wood and coal into the boiler (wood and coal 

particles conveyed pneumatically tend to separate at higher 

levels of wood content). The cost of equipping a plant to cofire 

commingled wood and coal ranges from $100 to $250/kW.10

Another method of cofiring is to process and feed wood and 

coal separately and feed each fuel into the boiler separately. The 

method uses a separate pulverizer especially designed for wood 

fuels and blows the pulverized wood, separately from the coal, 

into the boiler. A distinct advantage of this method is a greater 

10 Personal communication. 2006. Evan Hughes. Consultant. 30 Rondo Way, Menlo Park, CA 94025.

Figure 4.9—A diagram of an extraction steam turbine system. In principle 

and as shown in the diagram, the extraction system is a hybrid of the 

condensing and backpressure systems. As steam flows through the turbine, 

it will drop in pressure. Therefore, by addition of a port at the appropriate 

place on the turbine casing, steam can be extracted at a desired pressure 

and quantity. Thus, steam can be extracted and used for an industrial 

process or other application that requires more steam pressure and flow 

than can be provided with a backpressure turbine. 

Steam

Boiler

Pump

Condenser

Steam

Generator

Dry

kiln

Condensate
Chapter 4

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 45

capacity for handling wood, up to 10 to 20 percent more than 

the commingled method. Disadvantages include the possible 

problems of boiler derating or slagging and fouling at higher levels. 

Boiler derating occurs because the energy in wood (8,500 Btus 

per dry pound) is less than in coal (12,000 Btus per dry pound). 

Thus, if each pound of coal is replaced with a pound of wood, less 

electricity will be produced. Another disadvantage is the expense 

of feeding of fuels separately, with the cost of converting a plant 

to this method ranging from $200 to $300/kW or, if drying of the 

wood is required, up to $500/kW (see footnote 11). 

Another option for using wood at existing coal plants is to install 

a wood gasifier adjacent to the coal plant and feed gas from the 

gasifier into the coal boiler’s firebox. Gasification occurs at lower 

temperatures, mitigating slagging and fouling problems.11

A third option that is rapidly becoming available is to use a 

wood distillate product called bio-oil or pyrolysis oil, made by 

fast pyrolysis processes. With this option, small satellite plants 

located close to the biomass convert wood into distillate. The 

wood distillate, a liquid with considerably more energy per cubic 

foot than the wood, is then trucked to the plant. The higher 

energy density of the distillate translates into cheaper and simpler 

handling and operations. Fewer trucks are needed for transporting 

the fuel; and handling at the utility plant is streamlined because 

the need for truck scales, truck dumpers, wood storage, and other 

associated equipment has been eliminated. Instead, a typical 

fuel oil handling system consists of a fuel tank and pump for 

transferring the liquid into the boiler. Usually, existing ports in the 

boiler can be used to inject the distillate into the boiler. The alkali 

metals in the wood remain in the ash and char produced during 

the wood distillation process and, thus, are not an issue with the 

boiler (Badger and Fransham 2003). 

A process called reburning makes further use of wood in utility 

burners. Fuel, the wood distillate, is injected into the stack gas 

just above the main burner in the boiler where it burns under 

conditions of limited oxygen. The reburning converts the harmful 

nitrogen oxides in the emissions into elemental nitrogen, which 

is not harmful and is plentiful in our atmosphere (Brouwer and 

others 1997).

Selling Electricity to Others

The best way for an industry to maximize profits from power 

production is by using its power inhouse. Known as “behind 

the meter,” this use of power occurs on the customer side of the 

electric meter. Inhouse use directly offsets retail purchases of 

electricity and, thus, maximizes profitability. 

Another option for maximizing profit is to sell power back to the 

utility company, although such sales are usually not cost effective 

due to the low cost of utility-generated power. Some States have 

net metering laws that require utilities to purchase power at the 

same rate that they sell it to the customer. Most net metering 

requirements limit the amount of electricity that the utility must 

purchase to relatively small amounts, e.g., 100 kW, and also 

restrict the types of generation processes.

A third option is to sell electricity to a customer other than a utility 

company. However, most State regulatory bodies classify a utility 

as any entity that sells electricity to more than one customer, 

and such classification adds to an operation a significant level of 

regulation and associated expense. It may be possible to avoid 

regulatory restrictions by bringing in electric customers as project 

partners or offering alternate arrangements, e.g., selling the 

customer steam and letting the customer generate his or her own 

power (Wiltsee 1993). 

Permits and Regulations Related to Siting

The permits and regulations that apply to locating and installing 

a biomass conversion or processing facility cover land use, 

environmental concerns, and health and safety issues. States 

are responsible for enforcing environmental regulations 

established by the U.S. Environmental Protection Agency, but 

because States also can establish more stringent guidelines, 

wide variation in regulations may exist from State to State (U.S. 

Environmental Protection Agency 2006). 

Environmental regulations may cover air emissions from any 

source, including those that produce dust, as well as water quality 

related to wastewater emissions or runoff from biomass storage 

systems. Solid waste regulations may apply if wood is considered 

a waste or contains nonwood material, such as preservatives, fire 

retardants, or paints. Federal wetlands regulations may also apply. 

The primary permitting requirements usually pertain to air 

emissions, with particulates typically the emission of concern. 

Fortunately, particulate emissions are relatively easy to control 

with simple mechanical devices such as cyclones and baghouses. 

Land use regulations may include local zoning laws, building 

codes, permits to store combustible liquids onsite, and access 

to public roads (rights-of-way). If the proposed site is not 

already zoned for industrial, a variance or special permit will be 

required. Building codes may require approvals from the local 

fire department as well as electrical, mechanical, and plumbing 

inspections.

11 Personal communication. 2006. Thomas W. Johnson. Head. Research & Environmental Affairs Department, Southern Company Services Inc., 600 North 

18th St., Birmingham, AL 335226.
Biomass Conversion to Energy and Fuels

46 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Health and safety regulations include boiler permits and 

inspections as well as Federal Occupational Safety and Health 

Administration (OSHA) requirements. OSHA regulations 

require the presence of two people onsite when machinery is 

operating, although the second person can be employed in work 

independent of plant operations. 

The cost and time of obtaining permits and meeting regulatory 

codes can be significant. Local environmental firms familiar 

with State and local codes and procedures can help make sure 

all regulations are met and necessary procedures followed. No 

physical site preparation can be conducted until all permits are 

in place. Therefore, the permitting process should be given the 

utmost attention and adequate resources should be committed 

to its completion. 

CONCLUSIONS

Wood can be converted into fuel in solid, liquid, and gaseous 

forms and can supplement or replace any other energy source. 

Various types of wood-burning devices are commercially available 

and are built to handle specific requirements based on what form 

the wood is in, e.g., chips, sticks, or sawdust; the size of the burner 

required; and the form of energy needed, e.g., process heat or 

electricity. 

End-use options for wood energy include industrial process 

heat, space heating and cooling, and electricity generation. CHP 

systems efficiently generate power and use the leftover heat for 

industrial or commercial applications. District heating systems, 

whether used with CHP or as stand-alone heat sources, can create 

an economy of scale through centralized heat sources serving 

many customers in a concentrated geographical area. The most 

cost-effective industrial scenarios involve use of CHP systems and 

inhouse consumption of all onsite-generated electricity. 

The use of wood energy systems is likely to grow because 

the systems are easy to use, relatively cost effective, widely 

available, and supported by an existing production and supply 

infrastructure. 

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Diego, CA: Academic Press. 651 p.

Maker, Timothy; Penny, Janet. 1999. Heating communities with renewable 

fuels: the municipal guide to biomass district heating. Essex Junction, 

VT: Community Renewable Energy. 52 p. (available at www.

bioenergyupdate.com)

SERBEP. 1997. Tennessee biomass—La-Z-Boy of Tennessee [Fact sheet]. 

Muscle Shoals, AL: Tennessee Valley Authority. Prepared for the TVA/DOE 

Southeastern Regional Biomass Energy Program. 2 p.

Tennessee Valley Authority. 1991. Biomass design manual: industrial 

size systems. Muscle Shoals, AL: U.S. Department of Energy, 

Southeastern Regional Biomass Program. 176 p. (available at www.

bioenergyupdate.com)

Turick, C.E.; Peck, M.W.; Chynoweth, D.P. [and others]. 1991. Methane 

fermentation of woody biomass. Bioresource Technology. 37: 141–147. 

U.S. Environmental Protection Agency, Combined Heat and Power 

Partnership. 2006. Combined heat and power – an energy efficient 

choice for the ethanol industry. www.epa.gov/chp. [Date accessed: June 

21, 2006].

Wiltsee, G. 1993. Small-scale biomass fueled cogeneration systems—a 

guidebook for general audiences. Publ. TV–89669-2. Muscle Shoals, 

AL: U.S. Department of Energy, Southeastern Regional Biomass 

Energy Program; Tennessee Valley Authority. 31 p. (available at www.

bioenergyupdated.com)

Wiltsee, G. 1994. Heat activated cooling devices: a guidebook for general 

audiences. Publ. TV–89669-1. Muscle Shoals, AL: U.S. Department of 

Energy, Southeastern Regional Biomass Energy Program; Tennessee 

Valley Authority. 25 p. (available at www.bioenergyupdated.com)
Biomass Conversion to Energy and Fuels

48 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

absorption cooling system: a type of cooling system that causes 

cooling by absorbing a gaseous refrigerant in a fluid and then, 

in a separate operation, heating the fluid to release the energy 

in the refrigerant. 

alkali metal salts: primarily potassium and sodium metals in 

wood ash in the form of oxides, hydroxides, and metallo-organic 

compounds that may cause slagging and fouling when the 

wood is combusted. 

anaerobic digestion (also called biogasification): processes that 

use micro-organisms to break down organic materials under 

oxygen-free (anaerobic) conditions to produce a biogas. The 

process occurs in natural environments, and when it is made 

to occur in engineered environments, it is called anaerobic 

digestion (digestion since the organic matter is eaten and 

digested by the micro-organisms). 

anaerobic digester: a system of tanks and other equipment that 

employs an anaerobic digestion process to break down organic 

materials under oxygen-free (anaerobic) conditions to produce 

a biogas.

backpressure turbine: a steam turbine that does not condense 

the steam as it exits the turbine so that low-pressure steam is 

available for use in other applications. 

behind the meter: a reference to the electricity system that is 

located on the customer’s side of the utility meter. 

biogas: a combustible gas generated by an anaerobic digestion 

process that typically contains 50 to 70 percent methane, 30 to 

50 percent CO2

, and small amounts of other gases.

bio-oil (also called pyrolysis oil): a liquid product created by 

decomposing wood in the absence of oxygen and condensing 

the resulting vapor. Fast pyrolysis processes produce a woodderived bio-oil that looks similar to motor oil and has roughly 

80,000 Btus per gallon. 

boiler horsepower: equal to 33,478.8 Btus per hour (about 

9809.5 W).

CHP: (see combined heat and power system)

cofiring: the simultaneous burning of biomass and a fossil fuel, 

usually coal, in the same burner.

cogeneration system: (see combined heat and power system)

combined heat and power system (CHP): a system that 

generates electricity and then recovers the waste heat from the 

generation process for useful purposes. 

combustion (also called burning): a thermochemical process 

where a combustible material such as wood is heated to 

its ignition point in the presence of oxygen, causing it to 

decompose and burn. If adequate oxygen is provided, the 

process will continue until only ash (inorganic portion) is left. 

condensing turbine: a steam turbine that has a condenser at its 

steam outlet. 

direct combustion system: a method of combustion that burns 

wood in its solid form rather than gasifying or converting the 

wood into a liquid fuel before combustion takes place. 

district heating system: a system that uses one or more central 

plants, e.g., a boiler, and distributes heat via pipes to two or 

more buildings to supply space heat or hot water for domestic 

use.

dry anaerobic digester (also called a high-solids digester):

a type of anaerobic digester that uses a minimal amount of 

water, which allows smaller digesters to be as efficient as larger 

digesters. High-solids or “dry” anaerobic digesters are typically 

operated at a solids content of 35 percent. 

extraction turbine: a steam turbine that removes (extracts) a 

portion of the steam as it flows through the turbine. 

fast pyrolysis process: a thermochemical process where biomass 

materials are heated up to 750 to 1,000 °F in 

< 2 seconds in the absence of oxygen (so that combustion 

cannot occur), to cause wood to break down into gases, vapors, 

and char. The resulting vapors must also be condensed within 

2 seconds in order to recover a pyrolysis oil (also called bio-oil) 

that looks similar to motor oil. 

FBC system: (see fluidized bed combustion systems)

firetube boiler: boiler where the stack gases pass through boiler 

tubes that are surrounded by water. 

fluidized bed combustion (FBC) systems: burner systems that 

combust wood fuel on a high-temperature bed of finely divided 

inert material, such as sand, that is agitated by air blown from 

beneath the bed.

fouling: the formation of mineral deposits on the surface of boiler 

tubes and other heat transfer surfaces. Deposits are formed 

from an abundance of minerals—primarily alkali metal salts—in 

the wood, which create chemical compounds that allow the ash 

to melt when the wood is combusted. 

Glossary of Terms
Chapter 4

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 49

grate: a combustion chamber floor to support fuel, which can be 

inclined or horizontal and has openings to allow passage of air 

to aid in combustion and allow ash to fall through. Another type 

of grate is a wide moving chain across the bottom of the firebox 

that carries fuel through the combustion zone. 

high-solids digester (also called a dry anaerobic digester):

a type of anaerobic digester that uses a minimal amount of 

water, which allows smaller digesters to be as efficient as larger 

digesters. High-solids or “dry” anaerobic digesters are typically 

operated at a solids content of 35 percent. 

ignition temperature: the temperature at which combustion will 

become self-sustaining if enough fuel and oxygen are available. 

For wood, the ignition temperature is in the range of 270 to 290 °F.

independent power plant: a generating plant operated by a 

nonutility that sells its power to a utility. 

induction generator: a type of electricity generator that 

depends on the grid to supply voltage necessary to activate the 

generator’s magnetic fields. 

ligno-cellulose: materials that are primarily composed of 

cellulose, hemicellulose, and lignin. Typically, wood consists of 

40 to 45 percent cellulose, 20 to 30 percent hemicellulose, and 

20 to 30 percent lignin. 

liquefaction process: a thermochemical process that occurs 

under high pressure in the absence of oxygen to produce a 

liquid fuel that has an energy content similar to diesel fuel.

mesophillic: refers to a family of micro-organisms that prefers to 

grow in temperatures of 95 to 105 °F or an anaerobic digestion 

system that operates at similar temperatures. 

net metering: an arrangement that applies to customers of an 

electric power company that generate their own electricity and 

sell excess power to the utility. The customer pays or gets paid 

according to the net amount of electricity that flows back to 

the utility through his electric meter during each billing period. 

In some contracts, the amount a customer can sell back to the 

utility may be limited by law.

pile combustion system: a combustion system that burns wood 

fuel in either a heaped pile supported on horizontal or inclined 

grates, or in a thinly spread pile distributed across a traveling or 

stationary grate (see wet cell burner system).

process heat: heat used by industries for their manufacturing 

processes.

pulverized coal boiler: a boiler where coal is first reduced in size 

to a talcum powder consistency (pulverized) and then injected 

into the boiler so that it burns in suspension. 

pyrolysis oil (also called bio-oil): a liquid product created by 

decomposing wood in the absence of oxygen and capturing 

and condensing the resulting vapor. Fast pyrolysis processes 

produce a wood-derived bio-oil that looks similar to motor oil 

and has roughly 80,000 Btus per gallon. 

Rankine cycle: a process whereby steam is generated in a boiler 

and passed through a turbine to extract energy; then the steam 

exiting from the turbine is condensed and re-injected into the 

boiler, and the process is repeated. 

reburning: a pollution control process whereby fuel is burned 

in the stack gases from a boiler under conditions of limited 

oxygen. The process converts nitrogen compounds in the stack 

gases into elemental nitrogen. 

slagging: the formation of mineral deposits on the inside 

surface of combustion chambers. Deposits are formed from an 

abundance of minerals—primarily alkali metal salts—in certain 

types of wood, which create chemical compounds that allow 

the ash to melt when the wood is combusted. 

slow pyrolysis: a thermochemical process that occurs with limited 

oxygen and is commonly used to make charcoal.

slurry digester: a type of anaerobic digester that stirs the 

mixture inside the digester to keep the solid particles mixed in 

the liquid. These designs are operated at a solids content of 4 to 

20 percent.

spreader stoker: a device to meter and feed (stoke) fuel into a 

combustion device by spreading it across the grate or bottom of 

the firebox.

stoker: a method of feeding fuel to a burning device which may 

include using air to blow fuel into the combustion chamber, 

using augers to push fuel up from below the grate, mechanically 

spreading fuel onto a moving grate, or other methods. 

suspension combustion system: a burner system using either 

air or centrifugal force to suspend wood particles during the 

combustion process.

synchronous generator: a type of electricity generator that has 

a control system associated with it that allows the generator to 

automatically follow the cycles of grid-generated electricity. 

thermochemical process: a process that uses heat to cause 

chemical reactions that decompose biomass. One example 

of a thermochemical process involves heating wood above 

its ignition temperature in the presence of oxygen, causing 

it to burn. 
Biomass Conversion to Energy and Fuels

50 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

thermophilic: refers to a family of micro-organisms that prefers 

to grow in temperatures of 125 to 135 °F or an anaerobic 

digestion system that operates at similar temperatures. 

volatile solids: those solids in water or other liquids that are 

lost on ignition of dry solids at 550 °C (http://en.mimi.hu/

environment/liquid.html).

watertube boiler: a type of boiler where water flows through 

the boiler’s tubes and the stack gases are on the outside of 

the tubes.

wet cell burner system: a type of pile combustion system, usually 

consisting of a combustion chamber in the form of a vertical 

cylinder (see pile combustion system).

wood distillate: (see pyrolysis oil) 
 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 51

INTRODUCTION

The primary sources of low-cost woody biomass in the southern 

wildland urban interface (WUI) include urban wood waste, 

logging residues, and small-diameter timber such as pulpwood. 

The economic availability of these resources is determined by 

a combination of procurement, harvesting, processing, and 

transportation costs, and it affects the economic feasibility of 

bioenergy generation projects. Here we describe an approach to 

develop local woody biomass resource supply curves to assess 

delivered costs to the bioenergy generation facility at different 

levels of demand.

BACKGROUND

Physical Supply Versus Economic Availability

Woody biomass resources available in the southern WUI, 

including urban wood waste, logging residues, and pulpwood, 

are described in chapter 2. An evaluation of the feasibility of 

bioenergy generation requires an assessment of not only physical 

availability but also the economic availability of woody biomass 

resources. A comprehensive economic assessment of multiple 

woody biomass resources takes into account that delivered costs 

vary with biomass type and distance or travel time, which is used 

to estimate travel costs. When transportation costs are taken 

into account, more costly resources in close proximity may be 

economically competitive with cheaper resources further away, 

and vice versa. As generation capacity and demand for woody 

biomass intensifies, increasingly expensive and distant resources 

may need to be purchased. 

Supply Curves

A supply curve is a basic economic model used to describe and 

predict changes in the price and quantity of goods produced in 

competitive markets. A biomass resource supply curve is useful for 

estimating feedstock price at a given level of demand. Figure 5.1

illustrates a hypothetical woody biomass resource supply curve. 

Quantity Q1

 can be generated at marginal price P1 from urban 

wood waste, which is the cheapest resource because it is a zero- or 

negative-cost resource and widely available in the WUI. If biomass 

demand is increased due to higher levels of power generation 

capacity, more costly woody biomass resources, such as logging 

residues, might then be utilized to supply quantity Q2

 at price 

P2

. A more complex supply curve might include other available 

resources and would account for transportation cost in ranking 

the economic availability of these resources of different types at 

different travel times. 

Depending on local conditions, utility companies may or may not 

offer a premium for biomass resources that are more expensive 

Chapter 5

The Economic Availability of Woody Biomass

Matthew Langholtz, Douglas R. Carter, and Richard Schroeder

Q1 

P1 

Urban wood 

waste

Logging residues

Price (delivered $ MMBtus-1)

Q2

P2 

Supply (Btus per year)

Commercial 

timber

Figure 5.1—Hypothetical supply curve illustrating woody biomass resource categories.

Chapter 5
The Economic Availability of Woody Biomass

52 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

or further away. If utilities can price discriminate, the total cost to 

the utility to meet a specified generation capacity is calculated 

as the area under the curve, or the sum of price multiplied by 

quantity for each resource category employed. In the example 

below, the calculation to purchase Q2

 with price discrimination is 

(Q1

*P1)+(Q2*P2). However, some utilities may not be able or willing 

to differentiate between different biomass resources that have 

different costs. If utilities cannot price discriminate, the total price 

to acquire a given resource is the maximum price times the total 

quantity. In the example below, this calculation to purchase Q2

 is 

P2

*Q2, which would result in a higher total cost to the utility. 

Previous Biomass Supply Analyses

Biomass supply curves have been developed for large regions, 

which are appropriate for policy or macroeconomic analysis, and 

for local levels, which are needed to assess the economic viability 

of specific proposed bioenergy projects. National biomass supply 

curves suggest there are 268 million dry Mg (590 million green 

tons)1

 of agricultural waste, energy crops, forest residues, urban 

wood waste, and mill residues available in the United States 

annually. About 3 percent of this biomass is available at < $1.18/

GJ2

 [$1.25 per million British thermal units (Btus3)], which is close 

to the average price of coal sold to electric utilities in 2001 (Haq 

2003). Regionally, the economic availability of pulpwood biomass 

was assessed for 62 forest survey units in the Southeastern United 

States. It was concluded that total delivered costs of production 

ranged from about $18 to $23/dry Mg ($8 to $10 per green ton) 

in low-cost areas (northeast Florida, southern Georgia, southern 

Alabama, and the Coastal Plain of South Carolina) and $33 to 

$75/dry Mg ($15 to $34 per green ton) in high-cost areas (south 

delta of Louisiana, Kentucky, West Virginia and the mountains of 

Tennessee, and Virginia) in 1987 dollars at production levels up 

to 45 350/dry Mg/year (100,000 green tons) (Young and others 

1990, 1991). Delivered costs of biomass from dedicated feedstock 

supply systems (DFSSs) at various scales of analysis in the United 

States were estimated to range from < $22/dry Mg ($10 per green 

ton) to > $110/dry Mg ($50 per green ton) (Graham and others 

1997, Walsh 1998). For localized assessments, a Geographic 

Information System (GIS)-based tool to estimate quantities and 

costs of forest thinnings and residues from timber management 

units has been developed for applications in northern California 

(Chalmers and others 2003). These previous works assess biomass 

availability at regional levels or are limited to biomass from 

commercial forestry. 

METHODS

Developing localized woody biomass supply curves requires 

information about production costs and the physical availability 

of woody biomass resources in the area of interest. Here we 

describe our cost assumptions, the data used to estimate available 

woody biomass quantities, and methods to account for the spatial 

distribution of woody biomass resources. 

Cost Assumptions

The delivered cost of woody biomass, as with conventional forest 

products, can be defined as a sum of procurement, harvest, 

transportation, and miscellaneous management costs. These 

costs vary with local operational conditions, and ideally should 

be assessed for specific sites. We assemble southernwide cost 

assumptions, which could be modified with the availability of sitespecific cost information, and use a sensitivity analysis to assess 

the influence of increased production costs on the economic 

availability of woody biomass. The cost, operational, and wood 

density assumptions are described in this section and summarized 

in tables 5.1, 5.2, and 5.3. Urban wood waste, logging residues, 

and other potential woody biomass resources are described in 

more detail in chapter 2.

Procurement cost—Procurement cost is the amount paid to gain 

ownership of a biomass resource. Procurement cost is equivalent 

to the term “stumpage price” in the forest industry, i.e., the price 

paid to a timber owner for the right to harvest. Urban wood 

wastes and logging residues are bound to have low procurement 

costs. Urban wood waste handlers in the Southeastern United 

States typically pay a tipping fee, or disposal fee. Disposal fees 

nationwide range from $94 to $22/dry Mg ($51 to $12 per green 

ton) for landfilled wood and $21 to $2/dry Mg ($11 to $1 per green 

ton) for processed wood (Wiltsee 1998). Tipping fees for urban 

wood in the South typically range from $33 to $55/dry Mg ($15 

to $25 per green ton) delivered to a receiving area. This tipping 

fee translates into a negative procurement cost. Forest plantation 

owners pay postharvest site-preparation costs of about $462/ha 

($186 per acre), including raking and piling of logging residues 

(Smidt and others 2005), and removal of logging residue reduces 

these site-preparation costs for replanting plantations (Watson 

and Stokes 1989). Therefore, logging residues also represent a 

liability to the owner and are available at no or low cost (Watson 

and others 1986a). In this analysis, we assume procurement costs 

of −$27.56/dry Mg (−$15 per green ton) for urban wood waste, 

1

 Values are expressed as dry metric units followed by green imperial units. We assume moisture contents (green weight basis) of 37, 40, and 47 percent for 

logging residues, urban wood waste, and pulpwood, respectively, in our analysis, and assume 50 percent where not specified from referenced sources. The 

37-percent moisture content assumption for logging residues assumes air drying and excludes leaves.

2

 GJ = gigajoule or 1 billion joules, 1 gigajoule = 0.9478 MM Btu or about 116 dry pounds of wood. 3

 1 Btu = 1055 joules.
Chapter 5

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 53

Table 5.2—Operational assumptions 

Variable/attribute

Logging 

residue

Urban wood 

waste Pulpwood

Load and unload time per load (hours) 0.50 0.50 0.50

Load and unload cost per load (dollars) 25.00 25.00 25.00

Green tons per load 23.0 22.0 28.0

Load and unload cost per green ton (dollars) 1.09 1.14 0.89

Moisture content (green weight basis) (percent) 37 40 47

Ash content (percent) 5 5 2 

Load and unload cost per dry ton (dollars) 1.87 2.07 1.73

Haul cost (dollars per hour per load)a 75.00 75.00 75.00

Haul cost (dollars per hour per green ton) 3.26 3.41 2.68

Two-way haul cost (dollars per hour per dry ton) 11.24 12.40 10.40

Million Btus per dry ton 15.58 15.58 16.15

Harvest and process (dollars per dry ton) 24.00 30.00 24.00

Procurement cost (dollars per dry ton) 3.00 (25.00) 13.00

Percent of quantity assumed recoverable 90 60 100

a Based on prices received from trucking companies accounting for varying fleet age, weight, and expenses.

 

Table 5.1—Summary of cost assumptions for three woody biomass 

resourcesa

 

 Urban 

wood waste

Logging 

Cost Category residue Pulpwood

dollars dry/Mg (dollars per green ton)

Procurement costb −27.56 

(−15.00)

3.31

(1.89)

14.33

(6.89)

Harvest and process 33.07 

(18.00)

26.46

(15.12)

26.46

(12.72)

Load and unload 2.28 

(1.24)

2.06

(1.18)

1.91

(0.92)

One-way haul (per hour) 6.83

(3.72)

6.19

(3.54)

5.73

(3.12)

Example total delivered 

 cost of a 1-hour haulc 21.45

(11.68)

44.21

(25.27)

54.16

(26.77)

a Details used in calculating the costs are shown in table 5.2. b Negative costs for urban wood waste reflect disposal costs, known as “tipping fees.” c Equals the sum of two times the one-way haul cost and the remaining three cost categories.
The Economic Availability of Woody Biomass

54 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

which is estimated as an inexpensive tipping fee, and $3.31/dry 

Mg ($1.89 per green ton) for logging residues, based on typical 

procurement costs of $2 to $4/dry Mg ($1 to $2 per green ton) for 

logging residues in the South.4

A more expensive woody biomass resource that can be employed 

to meet demand beyond that available from waste resources is 

pulpwood. Pulpwood refers to small-diameter trees, typically 3.6 

to 6.5 inches d.b.h., that are usually harvested for manufacturing 

paper. An estimated 93.0 million m3

 (3.3 billion cubic feet) was 

harvested in the South in 2003 (Johnson 2003). For pulpwood to 

be economically competitive as a feedstock for energy, energy 

from the wood needs to be cheaper than energy from other 

sources (e.g., coal, natural gas, and solar energy) and the wood 

has to be offered a higher price for energy than for other uses 

(e.g., pulpwood [Sedjo 1997]). However, in conditions of low 

pulpwood stumpage prices and high biomass demand, some 

portion of this pulpwood supply could be allocated to bioenergy 

production (Perlack and others 2005). Southwide pine pulpwood 

stumpage prices reported by Timber-Mart South ranged from $10 

to $27/dry Mg ($5 to $13 per green ton) between 1995 and 2005, 

and averaged $13.62/dry Mg ($6.55 per green ton) over the four 

quarters of 2006. In this analysis, we assume pulpwood stumpage 

prices of $14.33/dry Mg ($6.89 per green ton). This estimate might 

be high because low-cost woody biomass from forest thinnings 

for habitat restoration, southern pine beetle control, timber stand 

improvement, and fuel load reduction (e.g., Bolding and Lanford 

2001, Bolding and others 2003, Mason and others 2006, Meeker 

and others 2004, Rummer and others 2004, Watson and Stokes 

1989) is likely to be purchased for bioenergy before it is necessary 

to buy merchantable pulpwood timber. Alternatively, if significant 

portions of pulpwood are required to meet demand, competition 

for pulpwood could drive prices higher. In a later sensitivity 

analysis, we increase procurement costs by 25 percent.

Harvest and processing costs—Harvest, processing, and 

transportation costs under various conditions are discussed 

in chapter 3. Harvest and transportation costs for urban wood 

waste and logging residues are typically higher than their 

procurement costs (fig. 5.2). Forest residue harvesting operations 

can use conventional skidding equipment or specialized woody 

biomass harvesting technology, might be harvested during or 

after conventional harvesting operations, and might be chipped 

in woods or delivered unchipped, depending on site-specific 

conditions and forest management objectives. In various studies, 

stump-to-truck wood harvest technologies and costs ranged from 

$11 to $68/dry Mg ($5 to $31 per green ton) (table 5.4) (Bolding 

and Lanford 2001, Hartsough and others 1997, Rummer and 

Figure 5.2—Transportation cost and sum of procurement, harvest, and processing costs of urban wood waste (UW), logging residues (LR), and pulpwood 

(PW) within a 2-hour haul travel time at 15-minute intervals. Transportation costs include loading and unloading costs. 

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

UW:

15

UW:

30

UW:

45

UW:

60

UW:

75

UW:

90

UW:

105

LR:

15

UW:

120

LR:

30

LR:

45

PW:

15

LR:

60

PW:

30

LR:

75

PW:

45

LR:

90

PW:

60

LR:

105

PW:

75

LR:

120

PW:

90

PW:

105

PW:

120

Resource and haul time category (minutes)

$ per million Btus, delivered

Transportation cost

Sum of procurement, harvest, and processing costs

Table 5.3—Wood density assumptions 

Species 

category Density

g/cm3 (pounds per cubic foot)

Hardwoods 0.513 (32) 

Softwoods 0.481 (30) 

4

 Personal communication. 2007. T. Harris, Publisher, Timber Mart-South, Center for Forest Business, Warnell School of Forestry and Natural Resources, 

University of Georgia, 180 E. Green Street, Athens, GA 30602-2152.
Chapter 5

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 55

others 2004, Watson and Stokes 1989, Watson and others 1986b). 

Costs typically are lower for plantation conditions than for natural 

stands, are lower for higher density stands and larger tracts, and 

can be reduced by combining the harvest of commercial timber 

and residues in one operation. The cost of whole-tree chips loaded 

into a trailer in the woods (hardwood and softwood) ranged 

from $23.85 to $32.37/dry Mg ($13.63 to $18.50 per green ton), 

including stumpage which typically cost $1 to $2 per green ton 

(Timber Mart-South 2006). On a dry weight basis, these costs 

would be increased for pulpwood having a higher moisture 

content, though they would be decreased on a green weight 

basis in a single-pass, whole-tree chipping operation. The cost 

of processing (chipping) urban wood waste varies, ranging from 

$14.20 to $60.63/dry Mg ($6.45 to $27.50 per green ton) in 2006 

Florida bids. In this analysis, we use harvest and chipping costs 

of $26.46/dry Mg ($15.12 per green ton) for logging residues and 

pulpwood and $33.07/dry Mg ($18 per green ton) for urban wood 

waste. We then measure the impact of increasing these costs 25 

percent.5 Other detailed assumptions applied in this analysis are 

shown in tables 5.1, 5.2, and 5.3. 

Table 5.4—Summary of published harvest costs (stump to truck) 

Year Author Region Operation Producta Cost Equivalent 2005b

---- $/dry Mg ($ per green ton) ----

2004 Rummer and others West Bundling EW 23.18 (10.50)c 24.58 (11.15)

2001 Bolding and Lanford Southeast Cut-to-length harvesting with 

small in-woods chipper

RW 17.13 (7.77) 17.68 (8.02)

EW 27.65 (12.54) 28.55 (12.95)

1994 Hartsough and others California Whole tree (plantation) EW 16.42 (7.45) 14.20 (6.44)

Hybrid (plantation) EW 12.02 (5.45) 10.38 (4.71)

Cut-to-length (plantation) EW 37.70 (17.10) 32.61 (14.79)

Whole tree (natural stand) EW 22.05 (10.00) 19.07 (8.65)

Hybrid (natural stand) EW 27.67 (12.55) 23.94 (10.86)

Cut-to-length (natural stand) EW 57.76 (26.20) 49.98 (22.67)

1989 Watson and others Alabama/

Mississippi 

Preharvest (plantation) EW 32.19–34.83

(14.60–15.80)

56.88–61.60

(25.80–27.94)

Mississippi Preharvest (natural) EW 33.38–35.74

(15.14–16.21)

58.97–135.80

(26.75–28.65)

Alabama Integrated (plantation) EW 22.29 (10.11) 39.40 (17.87)

1986 Watson and others Southeast Conventional 

(52-percent removal)

RW 13.78–22.27

(6.25–10.10)

33.64–54.39

(15.26–24.67)

One-pass 

(85-percent removal)

EW 18.30–22.38

(8.30–10.15)

44.69–54.65

(20.27–24.79)

Two-pass 

(76-percent removal)

EW 26.70–28.00

(12.11–12.70)

65.19–68.43

(29.57–31.04)

a EW = energy wood; RW = roundwood.

b Adjusted for inflation using the Bureau of Labor Statistics Produce Price Index for softwood logs and bolts to September of 2005 [http://data.bls.gov 

(Date accessed: September 27, 2005)].

c Based on $21.00 per bone dry ton assuming initial 50-percent moisture content on green weight basis.

5

 The cost of diesel fuel makes up approximately 25 percent of the total harvest and process cost. Increasing total harvest and process costs by 25 percent 

simulates a scenario in which the price of diesel is doubled.
The Economic Availability of Woody Biomass

56 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Transportation costs—Transportation costs vary with 

fuel price, travel time, road condition, biomass density, and 

handling characteristics, and can be 50 percent or more of the 

total delivered cost (see chapter 3). Mean roundtrip biomass 

transportation costs in Tennessee within an 80-km (50-mile) haul 

have been estimated at $8 to $18/dry Mg ($4 to $8 per green ton) 

(Graham and others 1997) and about $13/dry Mg ($6 per green 

ton) for haul distances of 97 km (60 miles) in Mississippi (Mitchell 

2006). Transportation costs have been estimated on a per km 

basis at 0.11cents/dry Mg/km (0.08 cents per green ton per mile) 

for short-rotation woody crops in Florida (Langholtz 2005) and 

ranging from 0.14 to 0.21 cents/dry Mg/km (0.10 to 0.15 cents per 

green ton per mile) for the Southeast (Rummer 2006). Hauling 

on roads with low speed limits increases transportation cost, 

and particularly affects overall costs of low-value wood products 

(Grebner and others 2005). To calculate transportation cost as a 

function of road conditions (see “Haul Time Calculations” below), 

we estimate transportation cost as a function of transportation 

time rather than distance. Based on the operational assumptions 

for each resource shown in table 5.2, we assume one-way 

transportation costs to be $7.52, $7.19, and $5.91/dry Mg/hour 

($3.41, $3.26, and $2.68 per green ton per hour) for urban wood 

waste, logging residues, and pulpwood, respectively. We then 

double these values to account for return trips with empty loads, 

and add $1.85 to $1.90/dry Mg (0.89 cents to $1.14 per green 

ton) to account for loading and unloading. These values are 

conservative compared to the hauling rate of 0.16 cents/dry Mg/

km (0.12 cents per green ton per loaded mile) reported by Timber 

Mart-South for the fourth quarter of 2006. In a sensitivity analysis, 

we increase total transportation costs by 30 percent.6

Total cost by resource-haul time category—Based on the 

above cost assumptions, we calculate the delivered cost of each 

woody biomass resource within a given haul time at 15-minute 

increments. We feel this approach most accurately reflects sitespecific variation in road networks, speed limits, and geographical 

constraints. By ranking these resources from lowest cost to highest 

cost, we estimate the progression of most to least economically 

available woody biomass resources, accounting for travel time 

from the point of delivery. Table 5.5 illustrates how, under these 

cost assumptions, urban wood waste requiring a one-way haul up 

to 105 minutes is cheaper than other woody biomass resources 

with shorter haul times. Transportation costs make up 10 to 84 

percent of total delivered costs, depending on the resource type 

and travel time (fig. 5.2). Costs could alternatively be calculated 

by haul distance rather than time, or transportation cost could 

be assumed uniform for each woody biomass resource within a 

maximum haul radius. The next step in constructing the woody 

biomass resource supply curve is to determine what quantity of 

biomass is available in each woody biomass resource-haul time 

category for a given community.

Physical Availability

In addition to production costs, information about the physical 

availability of resources is required to construct supply curves. 

We compile county-level woody biomass resource information 

for all counties in the Southern United States. To estimate 

woody biomass quantities from logging residues and pulpwood, 

we accessed Timber Product Output (TPO) reports (http://

srsfia2.fs.fed.us/php/tpo2/tpo.php) maintained by the Forest 

Service, Southern Research Station (SRS), Forest Inventory and 

Analysis Research Work Unit (FIA). This database provides forest 

inventory and harvest information, including annual yields of 

logging residues and pulpwood at the county level. The SRS 

derives these values by updating FIA harvest data with regional 

harvest information based on mill surveys.7 This information is 

useful because it estimates actual rather than potential logging 

residue and roundwood yields. Where potential woodsheds 

expand beyond the 13 Southern States and SRS TPO data are 

unavailable, we use data from the nationwide Timber Products 

Output Mapmaker Version 1.0 (http://ncrs2.fs.fed.us/4801/

timberproducts/index.htm), which uses the most recent available 

FIA inventory for each State. FIA allows a maximum error of 5 

percent per 1 billion cubic feet of growing stock on timberland at 

the State level. Errors are higher at the county level. See http://fia.

fs.fed.us/tools-data/other/default.asp for more information.

Because the pulpwood harvest identified in the FIA TPO report 

is currently used to produce pulp and paper products, not all of 

this resource is economically available for bioenergy. However, 

additional biomass is available from forest thinnings (Condon and 

Putz, in press; Perlack and others 2005), which is not included in 

this assessment. Furthermore, southwide softwood and hardwood 

growth exceeds removals (Adams and others 2003), indicating that 

more wood can be sustainably harvested. Recent trends of poor 

stumpage prices and loss of markets for forest products in the 

South may have reduced forest management activities (Smidt and 

others 2005), which could be mitigated by providing additional 

timber markets. 

We assume 0.111 dry Mg (0.244 green tons) of urban wood waste 

per capita annually (based on an average of 0.203 green tons at 

40-percent moisture content reported by Wiltsee 1998). Wiltsee’s 

study of 30 metropolitan areas across the United States showed 

relative consistency per capita nationwide; values tended to 

be higher in Southern States. This per capita estimate includes 

municipal solid waste wood from yard waste and tree trimmings 

but excludes an additional 0.1 dry Mg (0.2 green tons) per capita 

6

 The price of diesel is approximately 30 percent of the cost of operating a tractor trailer. Increasing total transportation costs simulates a scenario in which 

the price of diesel is doubled.

7

 Personal communication. 2007. Tony Johnson, Section Head of Resource Use, USDA Forest Service, Southern Research Station, Forest Inventory and Analysis, 

4700 Old Kingston Pike, Knoxville, TN 37919.
Chapter 5

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 57

per year reported from industrial wood, e.g., cabinet and pallet 

production, and construction and demolition debris. We multiply 

this average annual per capita yield by county level 2005 U.S. 

Census population estimates (www.census.gov/popest/counties/) 

to estimate total annual county yield of urban wood waste. We 

then use the method described below to estimate what portion of 

these county-level resources are within each resource-haul time 

category for a given delivery point.

Haul Time Calculations

GIS is a useful tool for identifying possible locations for 

bioenergy facilities (e.g., Young and others 1991); scheduling 

harvests of biomass resources (e.g., Chalmers and others 2003); 

and calculating transportation costs within woodsheds (e.g., 

Brewington and others 2001). We use GIS to calculate travel costs 

based on existing road infrastructure for each community and 

to assess the proportion of each county within a given haul time 

category. We assign speed limits to road features and divide 

road lengths by speed limits to estimate travel time. We increase 

haul time by 25 percent to account for operational delays and 

rerouting for bridges with gross vehicle weights < 36 Mg (40 tons), 

use ArcGIS®

 network analyst to calculate service areas based on 

travel time, and calculate the proportion of each county in each 

haul time category in 15-minute intervals. See text box below and 

Langholtz and others (2006) for more information about the use of 

ArcGIS®

 network analyst in this analysis. Rough estimates of woody 

biomass availability in each haul time category could be made 

using simpler techniques. 

Supply Curve Construction

After collecting information regarding quantities, distribution, 

and costs for each woody biomass resource, supply curves can 

be constructed. Assuming homogeneous distribution of woody 

biomass resources within counties (a necessary assumption given 

the FIA source data), we calculate the amount of woody biomass 

in each haul time category in each county, and then summarize 

quantities available from each resource-haul time category 

for the area of interest. We then assign total delivered costs for 

each resource-haul time category, and sort from least to most 

expensive (table 5.5). Supply curves are then plotted where the x 

axis is the cumulative total amount of woody biomass with each 

additional resource-haul time category and the y axis is total 

delivered cost. Curves can be plotted as an Excel®

 scatter plot or 

by using the Macro Economic Supply Curve Chart Excel®

 add-in. 

We express units based on energy content of the biomass, though 

units could be expressed as mass. See figure 5.3 for the steps used 

in constructing the woody biomass resource supply curves.

Assessing transportation cost based on haul time rather than distance accounts for road infrastructure 

in a woodshed. Haul times can be estimated by using 

GIS to account for speed limits assigned to U.S. Census 

Topologically Integrated Geographic Encoding and 

Referencing (TIGER) road layers. Following is a summary of 

steps that can be used to assess haul times by generating 

service areas with ArcGIS® Network Analyst:

1. Identify delivery point (county centroid, generation 

plant, etc.).

2. Identify area of interest (AOI) to include the maximum 

potential extent of the woodshed. A 450-km (280-mile) 

radius includes more than a 4-hour one-way haul. 

Identify counties within the AOI.

3. Download U.S. Census TIGER roads shapefiles for the 

AOI from http://arcdata.esri.com/data/tiger2000/tiger_

download.cfm. Merge the roads, define the projection 

(see Price and Coleman 2003), and reproject the merged 

roads layer. Keep all layers in the same projection.

4. Assign speed limits to each roads segment according 

to census feature class codes and calculate travel time 

(see Price and Price 2003). To account for expected 

travel delays, we increase calculated travel times by 25 

percent.

5. Calculate service areas based on haul time using the 

ArcGIS®

 Network Analyst Service Area Calculator (see 

Chandrasekhar 2005). We assess haul times based on 

15-minute haul intervals, and assume the “ToBreak” 

field value for each haul time category. Export service 

area polygons to a shapefile.

6. Union the service area polygons to the counties 

polygons and clip as necessary. Ensure the unioned 

shapefile is projected, add a “NewArea” field (float), and 

calculate areas of each feature. 

7. Add a “ConcCat” field (text) and concatenate the county 

name or “FIPS” field with the “ToBreak” field. Summarize 

the “ConCat” field including the average of the original 

area and the sum of the “NewArea” field. 

8. Import the summarized *.dbf to a spreadsheet software 

such as Excel®

. For each “FIPS-ToBreak” record, divide 

the “NewArea” by the original area to determine what 

percentage of each county is in each haul time category.

9. This percentage can be used to estimate what 

percentage of the woody biomass resource in each 

county resides in each haul time category. A Microsoft 

Excel®

 Pivot Table can then be used to summarize the 

estimated total of each biomass resource in each haul 

time category.
The Economic Availability of Woody Biomass

58 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Figure 5.3—Work flow diagram illustrating resources and steps used in woody biomass resource supply curve construction.

The percent of the area of each 

county in each haul time category 

is calculated and exported to 

Excel©. 

An Excel© Pivot Table is used to summarize 

the quantity of each biomass resource in each 

haul time category, and the costs of each 

product-haul time category are assigned. 

Product-haul time categories are sorted from 

least to most expensive, and supply curves are 

plotted. 

County-level biomass resource 

data is multiplied by the proportion 

of each county in a given haul 

radius to estimate the proportion 

of a county’s resources in each 

haul time category. 

Haul time categories are 

calculated from U.S. Census 

TIGER roads in ArcGIS Network 

Analyst©. 

County-level resource data are 

retrieved from FIA. Urban wood 

waste estimates are based on 

county populations (U.S. Census). 

Table 5.5—The 10 least expensive woody biomass resource-haul time categories within a 2-hour 

haul travel time ranked from least to most expensive (costs account for ash content) 

Resource 

Haul time category

(minutes) $/dry Mg ($ per green ton) $/GJ ($ per million Btu)

Urban wood waste 0–15 11.21 (6.10) 0.62 (0.65)

Urban wood waste 15–30 14.62 (7.96) 0.81 (0.85)

Urban wood waste 30–45 18.04 (9.82) 1.00 (1.05)

Urban wood waste 45–60 21.45(11.68) 1.19 (1.25)

Urban wood waste 60–75 24.87(13.54) 1.37 (1.45)

Urban wood waste 75–90 28.29(15.40) 1.56 (1.65)

Urban wood waste 90–105 31.70(17.26) 1.75 (1.85)

Logging residues 0–15 34.93(19.96) 1.92 (2.03)

Urban wood waste 105–120 35.12(19.12) 1.93 (2.04)

Logging residues 15–30 38.03(21.73) 2.09 (2.21)
Chapter 5

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 59

RESULTS

Twenty-eight counties were selected in the WUI of the 13 

Southern States as having potential for using woody biomass for 

energy generation (the county selection process is described in 

chapter 6 and selected States are shown in chapter 6, fig. 6.2). 

Approximate conversions of trillion Btus to MW, dry tons per year, 

truckloads per year, and homes powered per year are shown 

on the scales in figure 5.4. For the 28 counties, there was an 

average of 2.4, 9.1, and 18.0 trillion Btus of urban wood waste, 

logging residues, and pulpwood, respectively, within a 2-hour haul 

distance. Relative economic availability of woody biomass among 

the counties varies with quantity supplied. For example, of the 28 

counties assessed, results suggest Le Flore County, OK, has the 

highest marginal cost, i.e., cost of an additional unit, of biomass at 

quantities up to 7 trillion Btus, while Trimble County in Kentucky 

shows the highest marginal costs at demand above this amount 

(fig. 5.5). Typical demand is likely to be in the range of 2.3 to 4.7 

T Btus to produce about 20 to 40 MW of electricity, enough to 

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

0 10 20 30 40 50 60 70

(Trillion Btus per year)

$ per million Btus, delivered

Trimble Co., KY

Laurel Co., KY

Le Flore Co., OK

Average of 28 SE U.S. Counties

Douglas Co., GA

Coweta Co., GA

Lee Co., AL

Figure 5.5—Example of low, high, and average woody biomass supply curves of selected WUI counties. Biomass sources include urban wood waste, 

logging residues, and pulpwood within a 2-hour haul distance. The average supply curve includes 2.4, 9.1, and 18.0 trillion Btus of urban wood waste, 

logging residues, and pulpwood, respectively. Approximate conversions of trillion Btus to MW, dry tons per year, truckloads per year, and homes powered 

per year are shown on the scales in figure 5.4.

0 2 4 6 8 10 12 Trillion Btus/per year

0 10 20 30 40 50 60 70 80 90 100 110 Megawatts

0 100,000

10,000

10,000

200,000

20,000

20,000

300,000

30,000

30,000

400,000

40,000

40,000

500,000

50,000

600,000

60,000

700,000 800,000 Dry tons/year

0 Truckloads/year

0 Home powered/year

Figure 5.4—Scale showing general relationship between Btus per year, MW, dry tons of biomass per year, truckloads of biomass per year, and homes 

powered per year. Values are calculated based on 8.6 MW/trillion Btus (see chapter 6, table 6.2), 16 million Btus per dry ton of biomass, 23 green tons of 

biomass per truckload, and 400 homes powered per MW considering typical consumption in the South (Bellemar 2003). The actual proportions between 

these values vary with generating efficiency, moisture content, household energy consumption, and other factors. 
The Economic Availability of Woody Biomass

60 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

power 8,000 to 16,000 households in the South (Bellemar 2003). 

Quantities in this range cost $1.93 to $2.58/GJ ($2.04 to $2.72 

per million Btu) for the 28-county average cost curve. Under the 

average curve, demand up to 4.8 trillion Btus can be met with 

urban wood residues within a 2-hour haul, logging residues within 

a 1-hour haul, and pulpwood within a 30-minute haul (fig. 5.6).

Biomass literature typically suggests a maximum transportation 

distance of about 80 km (50 miles) for bioenergy to be 

economically viable. However, the supply curve in figure 5.6 

indicates that urban wood waste 105 minutes away, or about 

113 km (70 miles) away, can outcompete closer, more expensive 

resources. Limiting potential woody biomass resources to those 

available within a 1-hour haul radius excludes resources that might 

otherwise be available, and shows pulpwood at a 15-minute haul 

time to be cheaper than logging residues at a 1-hour haul time for 

the 28-county average curve (figs. 5.7 and 5.8). Excluding woody 

biomass resources beyond a 1-hour haul time shows a more 

conservative assessment of the economic availability of woody 

biomass to a community by reducing the area of the woodshed. 

Such a scenario might be indicative of conditions under increased 

competing demand spurred by multiple bioenergy generation 

facilities in a region.

We ran a sensitivity analysis to assess the impact of increasing 

costs on the economic availability of woody biomass resources. 

The analysis includes: (1) increasing procurement costs to 

$−20.67, $4.13, and $17.91/dry Mg ($11.25, $2.36, and $8.61 

per green ton) for urban wood waste, logging residues, and 

pulpwood, respectively; (2) increasing harvest and process costs 

by 25 percent; (3) increasing load and transportation costs by 

30 percent; and (4) adding all of these cost increases. Because 

each type of cost increase affects the three resources differently, 

the resource-haul time category ranking from lowest cost to 

highest cost changes slightly. Cumulative impacts of all three 

cost increases range from 0.52 cents per million Btus for logging 

residues at a 15-minute haul time to $1.40 per million Btus for 

urban wood waste at a 2-hour haul time, and vary by resourcehaul time category (fig. 5.9). Increasing transportation costs has a 

greater impact at longer travel times. 

0 15-30 minutes 0.1

30-45 minutes

0.4

45-60 minutes 

0.7

60-75 minutes

1.1

75-90 minute

1.5

90-105 minutes

1.9 0-15 minutes 2

105-120 minutes

2.5

15-30 minutes

2.8

30-45 minutes

3.3 0-15 minutes 3.4

45-60 minutes

4.2

15-30 minutes

4.8

0.00

0.50

1.00

1.50

2.00

2.50

3.00

(Trillion Btus per year)

$ per million Btus, delivered

Urban wood waste

Logging residues

Pulpwood

s

Figure 5.6—Prices, quantities, and resource-haul category composition up to 4.8 trillion Btus, based on the average of 28 

selected counties in the WUI. Approximate conversions of trillion Btus to MW, dry tons per year, truckloads per year, and 

homes powered per year are shown on the scales in figure 5.4.
Chapter 5

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 61

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

0 2 4 6 8 10 12 14

(Trillion Btus per year)

$ per million Btus, delivered

Sevier Co., TN

Trimble Co., KY

Blount Co., TN

Average of 28 SE U.S. Counties

Douglas Co., GA

Lee Co., AL

Coweta Co., GA

Figure 5.7—Example of low, high, and average woody biomass supply curves of selected WUI counties. Sources 

include urban wood waste, logging residues, and pulpwood within a 1-hour haul radius. The average supply curve 

includes 0.7, 1.7, and 3.4 trillion Btus of urban wood waste, logging residues, and pulpwood, respectively, as shown in 

figure 5.8. Approximate conversions of trillion Btus to MW, dry tons per year, truckloads per year, and homes powered 

per year are shown on the scales in figure 5.4. 15-30 minutes 0.1 30-45 minutes 0.4 45-60 minutes 0.7 0-15 minutes 0.8 15-30 minutes 1.0 30-45 minutes 1.6 0-15 minutes 1.7

45-60 minutes

2.5

15-30 minutes

3.1

30-45 minutes 

4.1

45-60 minutes

5.8

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

(Trillion Btus per year)

$ per million Btus, delivered

Urban wood waste

Logging residues

Pulpwood

Figure 5.8—Prices, quantities, and resource-haul category composition within a 1-hour haul distance, based on the average of 28 

southern counties in the WUI. Approximate conversions of trillion Btus to MW, dry tons per year, truckloads per year, and homes 

powered per year are shown on the scales in figure 5.4.
The Economic Availability of Woody Biomass

62 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0 1 2 3 4 5 6 7 8 9 10 11 12

(Trillion Btus per year)

$ per million Btus, delivered

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

0 5 10 15 20 25 30

(Trillion Btus per year)

$ per million Btus, delivered

Original cost assumptions

Procurement costs increased 25%

Harvest and process costs increased 25%

Transportation costs increased 30%

Cumulative cost increases

Original cost assumptions

Procurement costs increased 25%

Harvest and process costs increased 25%

Transportation costs increased 30%

Cumulative cost increases

(A)

(B)

Figure 5.9—Average supply curves of 28 southern WUI counties: (A) including 2.4 and 9.1 trillion Btus of urban wood waste 

and logging residues within a 2-hour haul distance, and (B) including an additional 18.0 trillion Btus of pulpwood within a 

2-hour haul distance. Curves represent (1) original cost assumptions; (2) procurement costs increased to −$20.67, $4.13, and 

$17.91/dry Mg (−$11.25, $2.36, and $8.61 per green ton) for urban wood waste, logging residues, and pulpwood, respectively; 

(3) harvest and process costs increased 25 percent; (4) load and transportation costs increased 30 percent; and (5) the sum of 

all cost increases. Approximate conversions of trillion Btus to MW, dry tons per year, truckloads per year, and homes powered 

per year are shown on the scales in figure 5.4.
Chapter 5

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 63

CONCLUSIONS AND RECOMMENDED 

FUTURE RESEARCH

These supply curves illustrate local economic availability of woody 

biomass resources and prices that might be paid as a function of 

demand. Conclusions and stipulations include the following:

• On average for the 28 counties included in this study, up to 

3.3 trillion Btus of woody biomass are typically available at < 

$2.27/GJ ($2.39 per million Btus) in WUI communities in the 

Southeastern United States. This biomass consists of urban 

wood waste within a 2-hour haul and logging residues within a 

45-minute haul. 

• Low-cost biomass resources, such as urban wood waste within a 

haul time of 2 hours or about 130 km (80 miles), can be cheaper 

than pulpwood and other resources available with shorter travel 

times. 

• Woody biomass resources will become more expensive if 

multiple bioenergy efforts increase demand or when oil 

prices rise. Average maximum prices up to 4.0 trillion Btus are 

projected to increase to $2.73/GJ ($2.88 per million Btus) if the 

maximum haul radius is constrained to 1 hour and up to $3.44/

GJ ($3.63 per million Btus) if, in addition, all assumed price 

increases are applied. 

• Pulpwood resources included in this analysis assume current 

market prices. However, competing demand for this resource 

may increase prices.

• Opportunities may exist to use the cheapest woody biomass 

within a 2-hour haul radius to streamline bioenergy generation 

systems in anticipation of future reduced woodsheds resulting 

from increased competing demand.

Possible topics for future research include analysis of short- and 

long-run pulpwood supply and price impacts from alternative 

demand scenarios, alternative modes of transportation including 

rail and barge, potential woody biomass sources such as forest 

thinnings and DFSS, the use of hurricane debris for bioenergy 

generation, the impacts of hurricanes on the availability and 

sustainability of woody biomass, the impacts of forest industry 

and land use trends on the availability of woody biomass, and 

compensation for CO2

 mitigation or other incentives for renewable 

energy. Given higher resolution data from remote sensing, a 

more robust approach could be used to account for intracounty 

distribution of woody biomass resources. Because assumptions 

made in this analysis may not reflect local conditions, a decision 

support system could be developed to account for site-specific 

information for localized assessments. 

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Sedjo, R.A. 1997. The economics of forest-based biomass supply. Energy 

Policy. 25(6): 559–566.

Smidt, M.; Silveira Folegatti, B.; Dubois, M. 2005. Costs and cost trends for 

forestry practices in the South. Forest Landowner. 64(2): 25–31.

Timber Mart-South. 2006. Quarterly market reports. Athens, GA: University 

of Georgia, Warnell School of Forest Resources, Center for Forest 

Business. 5 p.

U.S. Dept. of Commerce, B. o. t. C. (2000). “United States census 2000.” 

http://www.census.gov/population/socdemo/migration/. [Date 

accessed: July 27, 2005].

Walsh, M.E. 1998. U.S. bioenergy crop economic analyses: status and needs. 

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Watson, W.; Ragan, J.; Straka, T. [and others]. 1986a. Economic analysis of 

potential fuelwood sources. In: Forests, the world and the profession: 

Proceedings of the 1986 Society of American Foresters national 

convention. Birmingham, AL: Society of American Foresters: 339-342. 

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Watson, W.F.; Stokes, B.J.; Savelle, I.W. 1986b. Comparisons of two methods 

of harvesting biomass for energy. Forest Products Journal. 36(4): 63–68.

Wiltsee, G. 1998. Urban wood waste resource assessment. Golden, CO: 

National Renewable Energy Laboratory. 177 p.

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economic availability of woody biomass for the Southeastern United 

States. Bioresource Technology. 37(1): 7–15.
Chapter 5

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 65

Glossary of Terms

Btu: British thermal unit or 1,055.06 joules

DFSS: Dedicated feedstock supply system

FIA: Forest Inventory and Analysis of USDA Forest Service

GIS: Geographical information system

GJ: gigajoule or billion joules

MMBtu: million British thermal units

SRS: Southern Research Station of USDA Forest Service

TPO: Timber Product Output report of USDA Forest Service

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 67

INTRODUCTION

Biomass energy facilities are often viewed in the context of local 

economic development efforts because utilization of biomass 

resources, instead of imported fossil fuels, results in greater 

retention of money in the local economy, leading to enhanced 

economic activity, income, and wealth. However, such facilities 

may be costly investments, on the order of tens of millions of 

dollars, which represents a substantial financial burden. Therefore, 

as a part of the public decisionmaking process, stakeholders must 

carefully consider overall benefits and economic impacts of such 

projects. Development of a biomass energy facility may have 

significant implications for other sectors of the local economy by 

posing new demands for biomass producers, equipment vendors, 

and other allied businesses, and with associated changes in 

employment and income. Economic impact analysis is a wellestablished methodology for evaluating the overall economic 

effects of an actual or proposed change in some specific activity, 

such as a new or expanded biomass-fueled power plant, in a local 

or regional economy. 

Local economies may be viewed in terms of basic activities that 

sell goods and services to markets located outside the local area, 

and service activities that provide goods and services to local 

businesses and residents. Basic industries attract money from 

outside to the local economy; this money then circulates in the 

local area through spending and respending by service industries 

and by employees of businesses. Money generated by the basic 

industries starts a chain of spending that supports the services 

segment of the local economy. New dollars eventually are lost 

from the local economy (leakages) in the form of tax payments 

to State and Federal Government, savings, profits that accrue to 

nonresidents, and payments for goods and services imported from 

outside the local area. The development of biomass-fueled power 

plants reduces this leakage by substituting locally produced fuels 

for imported fuels. Also, beneficial use of waste biomass materials, 

such as urban tree debris and forestry residues, adds to the overall 

resource base. 

The structure of a local economy with a biomass energy sector 

and the linkages that give rise to economic impacts are illustrated 

in figure 6.1. Businesses in the energy sector, including timber 

growers, loggers, and electric power producers, sell their 

products and services to intermediate and final consumers 

through wholesale and retail distributors, both within the local 

Chapter 6

Economic Impact Analysis of 

Woody Biomass Energy Development

Alan W. Hodges

Forest 

Resource 

Mgmt & 

Timber 

Production

Rest of 

United 

States 

and 

World 

Economy 

Wholesale 

& Retail 

Distribution

Exports

Resident 

Population 

Employee 

Households

Input & 

Service 

Suppliers

Local 

Consumption 

& 

Intermediate 

Demand

Economic Structure of the Wood Energy Industry

Jobs: 

Labor/ 

Wages

Local Economy Goods & Services 

and Monetary Flows

ImportsLeakages 

Consumer Household 

Spending-Induced 

Effects 

Purchased 

InputsIndirect 

Effects 

Logging & 

Forestry 

Services Wood Energy 

Industry

Local & 

State 

Government

Personal & 

Business Taxes 

Electric 

Utilities and 

Other Wood 

Users

Logging, 

Landscape, 

Transportation 

Services

Plant 

Engineering, 

Construction, 

Infrastructure

Figure 6.1—Structure and economic impacts of the wood energy industry in a local economy.

Chapter 6
Economic Impact Analysis of Woody Biomass Energy Development

68 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

economy and to the rest of the Nation and the world. Firms that 

purchase inputs from local suppliers generate economic activity 

through recirculation of money in the local economy. Employee 

households spend their earnings for personal consumption 

of food, clothing, housing, transportation, etc., which further 

increases economic activity. Also, businesses and households pay 

taxes to local governments. 

Economic impacts may be evaluated in terms of various measures 

that represent different aspects of economic activity. Output 

represents the total revenue generated by an industry, including 

sales, plus changes in business inventories. Employment is another 

important economic measure, represented simply by the number 

of jobs, or in some cases the number of full-time equivalents, 

including part-time or seasonal employees. Value added is a broad 

measure of income, reflecting all personal and business income, 

plus change in net capital investment, and is a preferred measure 

of net economic contribution because it avoids double counting 

of impacts among vertically linked sectors that may occur with 

output. Value added can also be construed as the difference 

between industry output and the value of purchases from other 

industry sectors, and the sum of value added for all industry 

sectors in a region represents the gross regional product, which 

is equivalent to the gross domestic product at the national level. 

Labor or “earned” income represents all wages and salaries and 

other payroll benefits paid to employees, and proprietor’s income 

received by business owners, but excludes retirement income, 

welfare, and other transfer payments. Other property income 

includes dividends to corporate stockholders, capital gains, and 

interest income. Indirect business taxes represent taxes paid 

by businesses, such as payroll taxes, sales taxes, property taxes, 

and motor vehicle taxes, etc. All or some of these measures of 

economic impacts may be used in certain cases, depending upon 

the issues of concern.

Further discussion on the technical background of input-output 

analysis and use of the impact analyses for planning (IMPLAN) 

software and databases for regional economic impact analysis is 

provided in the appendix to this chapter.

CASE STUDIES OF WOOD-FUELED POWER PLANTS

The application of regional economic impact analysis for 

development of wood-fueled power plants was demonstrated 

through case studies of 28 selected counties in the Southern 

United States. The counties were identified as being favorable 

locations for wood-fueled power plants based on a variety 

of resource and socioeconomic indicators. The availability of 

biomass forest resources was considered for forests that do 

not have any administrative restrictions on commercial use, 

such as commercial timberlands and most national forests, but 

excludes parks, preserves, and wilderness areas. Data on total 

forest biomass, including tree tops, stumps, and small-diameter 

trees that would not normally be harvested for commercial 

timber products, were taken from the latest published inventory 

estimates (Pugh 2004). Information on urban wood waste 

resources was compiled from various State waste management 

agencies, which provided this data for 7 of the 13 States. 

Information on population, population growth (1990–2000), 

personal income, income growth, and per capita income were 

provided by the U.S. Census Bureau (2004). Information on 

wildland-urban interface (WUI) areas was used as an indicator 

of populations that are near to biomass resources. WUI and 

“intermix” areas, analyzed at the census tract level, are defined 

as having a housing density of more than one unit per 40 acres, 

and located within 1.5 miles of an area of at least 1,325 acres 

that is 75 percent or more vegetated (Stewart and others 2005). 

Another factor considered was the existing output of electric 

power generators, as reported by U.S. Department of Energy (U.S. 

Department of Energy 2004).

In order to identify suitable counties for case studies of economic 

impacts of woody biomass power development, an index was 

developed. The socioeconomic and biomass resource indicators 

for each county were expressed as rank scores from zero to 1, 

with the highest value being 1 and intermediate values scaled 

proportionally. These variables were then combined into an overall 

index of suitability defined as:

S = FB x (PD + PG + PIPC + PIC + WUI + E + UW)

where

S = overall suitability

FB = forest biomass per unit area

PD = population density

PG = population growth

PIPC = personal income per capita

PIC = personal income change

WUI = share of area in wildland-urban interface

E = existing electric power generation per capita, and

UW = urban woody waste generation per capita

The variable for forest biomass per unit area was deemed to be of 

critical significance, and so was specified as a multiplicative factor 

in this equation, while all other terms were additive. Counties were 

ranked according to overall scores on this suitability index, and the 

top-ranked five counties in each State were selected for further 

consideration. The final list of counties for case studies was chosen 

to provide a mix of different ecosystem and community types. 

Also, local and State officials were contacted to confirm interest 

and suitability of the communities identified. 

The socioeconomic characteristics of the 28 selected counties 

are summarized in table 6.1, and the locations of the counties 

are shown on the map in figure 6.2. Generally, these counties 

were fast growing, with above-average personal income and 

population densities, and had a relatively high share of their area 

in the WUI intermix. In some States (Florida and Georgia) four or 

more counties were selected for case studies, while other States 

(Louisiana, Oklahoma, South Carolina, and Texas) had only one 
Chapter 6

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 69

selected county. Forest biomass available ranged from 11 to 32 

short tons per acre; county area ranged from 152 to over 1,600 

square miles; populations ranged from < 10,000 to over 300,000 

persons; population density ranged from 42 to 633 persons per 

square mile; population growth during 1990 to 2000 ranged from 

−2 to over 60 percent; personal income per capita ranged from 

about $17,000 to over $34,000; share of area in WUI ranged from 6 

to 81 percent. 

Costs for Power Plant Construction and Operation

Wood fuel requirements for power plants were evaluated for 

small and medium scales of operation, 20 and 40 MW. Energy 

requirements for these plants were calculated at 2.327 and 4.653 

trillion British thermal units (Btus), respectively, based on plant 

operating rates, typical heating values for biomass, and thermal 

efficiency for conversion of heat energy into electric power (16,000 

Btus/kW/hour), as shown in table 6.2. Fuel typically represents the 

largest operating expense for a power plant. The costs for wood 

fuel to meet these energy requirements were estimated separately 

for each case-study county based on an analysis of wood biomass 

supplies of logging residues, stumps, and urban waste wood, 

which accounted for local collection and transportation costs (see 

chapter 5). Fuel costs averaged $4.0 and $9.8 million for the 20 or 

40 MW plants, respectively, and ranged from $5.7 to nearly $13 

million for the 40-MW plant across the selected counties, due to 

differences in availability of wood resources and transportation 

infrastructure (table 6.3). 

The basic information on capital expenses for power plant 

construction and operating expenses were provided by Carlson 

Consultants, a consulting engineering firm for wood-fueled 

power plants, as shown in table 6.4. Total construction costs were 

valued at $48.7 million for the 20-MW plant and $86.8 million 

for the 40-MW plant, including land, sitework, building, plant 

equipment, and engineering fees. The largest expense items 

were the boilers and turbines, at $45 to $90 million. The total 

Table 6.1—Socioeconomic characteristics of selected Southern U.S. counties for woody biomass power development case studies 

County, State Area

Population 

(2003)

Population 

density 

Population 

change 

1990–2000

Personal 

income 

per capita

Forest area 

unreserved 

Share area 

interface 

Forest 

biomass 

available

Annual 

woody 

waste per 

capita

Annual 

power 

generation 

per capita

mile2

M

person per

mile2

percent dollars acres percent tons per 

acre

tons MWh

Lee, AL 600 119,561 199 32 21,445 393,991 46 18 NA 25

Shelby, AL 798 159,445 200 44 34,819 418,341 50 20 NA 74

Saline, AR 737 87,554 119 30 24,674 571,054 36 26 NA 0

Union, AR 1,061 44,829 42 −2 28,974 675,441 13 29 NA 58

Alachua, FL 976 223,578 229 20 25,280 604,986 43 11 0.05 8

Clay, FL 652 157,502 242 33 26,739 410,846 40 16 0.02 0 

Leon, FL 704 242,577 345 32 28,056 448,549 38 16 0.13 4 

Nassau, FL 612 61,625 101 31 31,298 463,899 28 18 0.03 9

Santa Rosa, FL 1,045 133,092 127 44 24,576 738,121 28 16 0.13 1

Coweta, GA 454 101,395 223 66 26,932 285,445 63 19 NA 57

Douglas, GA 200 102,015 510 30 26,085 126,809 79 27 NA 0 

Murray, GA 355 39,446 111 40 20,400 214,373 40 26 NA 45

Union, GA 335 19,119 57 44 23,270 186,122 48 26 NA 1 

Laurel, KY 447 55,488 124 21 20,468 282,223 56 26 0.02 2

Trimble, KY 152 8,759 58 33 17,109 99,998 45 25 0.02 498

Livingston, LA 681 102,046 150 30 21,336 449,851 53 25 NA 0 

DeSoto, MS 499 124,378 249 58 27,261 317,949 19 15 0.17 5 

Warren, MS 639 48,993 77 4 27,189 396,049 21 29 0.05 19

Buncombe, NC 653 212,672 326 18 27,288 416,687 72 30 0.06 10

Orange, NC 400 118,183 295 26 33,375 255,316 81 26 0.11 1

Le Flore, OK 1,639 48,896 30 11 19,776 1,007,238 6 15 NA 42

Oconee, SC 683 68,523 100 15 25,209 413,423 50 18 0.08 265

Anderson, TN 342 71,904 211 5 27,100 220,692 59 32 0.03 75

Blount, TN 569 111,510 196 23 25,353 267,666 39 24 0.04 5

Sevier, TN 605 75,503 125 39 24,603 255,145 56 27 0.06 7

Montgomery, TX 1,106 344,700 312 61 32,688 685,399 59 21 NA 5 

Chesterfield, VA 437 276,840 633 24 33,586 278,264 64 25 NA 30

Fluvanna, VA 288 23,078 80 61 23,845 185,753 44 23 NA 60

NA = data not available. 
Economic Impact Analysis of Woody Biomass Energy Development

70 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Figure 6.2—Location of counties in the Southern United States selected for case studies.

Table 6.2—Fuel requirements for a 20- and 40-MW wood-fired power plant 

Factor Datum

Total hours per year 8,760

Capacity factor 0.83

Total operating hours per year 7,271

Heat rate: Btus/kWh electricity 16,000

Total annual energy input required (trillion Btus) 

20 MW 2.327

40 MW 4.653

Btu = British thermal unit.

Source: Quaak and others (1999).
Chapter 6

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 71

annual operating expenses (first year) for the model wood-fueled 

power plant were $8.0 million for 20 MW to $16.1 million for 40 

MW, including average fuel costs as discussed above. In terms of 

the earlier discussion, these values reflect the direct effect of the 

new facility. The construction expenditures are a one-time event 

that was assumed to occur within a year, while plant operating 

expenditures are annually recurring impacts. It was assumed 

that all purchases were made locally, except in some cases 

where particular inputs may not be available locally because the 

producing sector does not exist in the county. 

Economic Impact Results

The economic impacts of a 20- and 40-MW wood-fueled power 

plant were evaluated in each of the case-study communities 

(counties) using the IMPLAN software and regional databases (see 

appendix for details). 

The estimated economic impacts resulting from the construction 

phase of power plant development in each of the counties are 

summarized in table 6.5. Total output impacts for a 20-MW power 

plant averaged $11.9 million and ranged from $2.8 to $45.3 

Table 6.3—Biomass fuel costs for 20- and 

40-MW power plants in selected Southern 

U.S. counties 

County, State 20 MW 40 MW 

million dollars 

Lee, AL 4.003 9.552

Shelby, AL 4.028 10.375

Saline, AR 4.850 11.443

Union, AR 5.021 10.912

Alachua, FL 3.840 9.278

Clay, FL 3.375 9.051

Leon, FL 4.522 10.569

Nassau, FL 3.690 9.464

Santa Rosa, FL 4.699 11.233

Coweta, GA 2.610 6.124

Douglas, GA 2.466 5.698

Murray, GA 3.702 8.697

Union, GA 4.763 11.650

Clark, KY 3.769 9.850

Laurel, KY 4.485 10.516

Trimble, KY 3.572 8.790

Livingston, LA 3.624 9.100

DeSoto, MS 3.557 9.803

Warren, MS 4.620 10.518

Orange, NC 2.880 7.375

Le Flore, OK 5.879 12.975

Buncombe, NC 3.741 9.371

Oconee, SC 4.079 10.298

Anderson, TN 4.531 11.581

Blount, TN 4.638 11.970

Sevier, TN 4.643 12.099

Montgomery, TX 2.815 6.434

Chesterfield, VA 3.811 10.224

Fluvanna, VA 4.056 10.042

 Average 4.009 9.827
Economic Impact Analysis of Woody Biomass Energy Development

72 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Table 6.4—Capital and operating costs for a 20- and 40-MW wood-fueled power plant 

IMPLAN 

sector(s) Description 20 MW 40 MW 

$1000

Capital construction costs

39 Site preparation (highway, street) 800 1,000

40 Water, sewer, and pipeline construction 100 150

238 Power boiler and heat exchanger manufacturing 22,250 40,500

285 Turbine and turbine generator set units manufacturing 22,250 40,500

394 Initial fuel delivery (truck transportation) 300 500

429 Financing cost (funds, trusts, and other financial vehicles) 1,500 2,500

431 Site acquisition (real estate) 1,000 1,000

445 Permitting (environmental and other technical consulting) 500 600

 Total 48,700 86,750

Annual operating costs (1st year)

14–18

Wood fuel cost, average for all counties (allocated equally to 

logging, agriculture, and forestry support services) 4,009 9,827

30 Utility interconnection (power generation and supply) 100 155

31 Start-up fuel, gas (natural gas distribution) 25 50

32 Utilities, electric 50 75

150 Consumable chemicals 330 660

238 Power boiler and heat exchanger manufacturing 50 90

285 Turbine and turbine generator set units manufacturing 50 90

428 Insurance (insurance agencies, brokerages, and related) 160 260

434 Mobil equipment lease 90 120

439 Routine and periodic maintenance 1,000 1,650

445 Environmental costs 100 160

451 Corporate overhead (management) 100 120

452 Office expenses 110 140

460 Ash disposal 60 120

499 Property tax 470 800

10006 Salaries and benefits 1,260 1,820

 Total 7,964 16,137

IMPLAN = impact analyses for planning.

Source: Carlson Small Power Consultants, Redding, CA.
Chapter 6

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 73

Table 6.5—Capital construction impacts for 20- and 40-MW wood-fueled power plants in selected 

Southern U.S. counties 

 

County, State

20-MW plant 40-MW plant 

Output Employment 

Value 

added Output Employment 

Value 

added 

million $ no. jobs - - - - - - million $ - - - - - no. jobs million $ 

Lee, AL 5.0 60 2.9 6.0 72 3.4

Shelby, AL 40.9 317 18.9 71.2 549 32.5

Saline, AR 4.1 52 2.3 4.9 61 2.7

Union, AR 4.0 46 2.3 4.8 55 2.7

Alachua, FL 8.0 81 4.3 10.8 107 10.8

Clay, FL 7.6 74 3.7 10.3 98 4.8

Leon, FL 7.8 74 4.1 10.7 100 5.4

Nassau, FL 6.7 63 3.3 9.0 82 4.2

Santa Rosa, FL 37.7 335 15.4 65.5 578 26.3

Coweta, GA 7.5 49 2.7 5.6 59 3.1

Douglas, GA 7.6 69 3.6 10.2 90 4.6

Murray, GA 3.1 31 1.7 3.8 39 2.0

Union, GA 4.0 47 2.2 4.8 57 2.6

Laurel, KY 4.5 54 2.6 5.4 64 3.1

Trimble, KY 2.8 27 1.7 4.6 43 2.7

Livingstone, LA 35.0 293 17.2 61.2 504 29.9

DeSoto, MS 4.8 59 2.7 5.8 70 3.1

Warren, MS 4.4 54 2.4 5.2 64 2.8

Buncombe, NC 7.9 74 3.9 10.7 98 10.7

Orange, NC 45.3 379 25.9 78.7 653 44.9

Le Flore, OK 5.8 65 2.5 7.8 83 3.0

Oconee, SC 4.2 45 2.4 5.0 54 2.8

Anderson, TN 6.7 57 3.6 9.1 76 4.7

Blount, TN 4.9 48 3.0 5.9 58 3.6

Sevier, TN 6.7 59 3.5 11.5 229 7.0

Montgomery, TX 7.8 64 4.1 10.6 85 5.4

Chesterfield, VA 43.8 222 22.1 76.2 372 38.2

Fluvanna, VA 3.9 40 2.1 4.7 50 2.5

Average 11.9 101 6.0 18.6 159 9.6
Economic Impact Analysis of Woody Biomass Energy Development

74 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

million; employment impacts averaged 103 jobs and ranged 

from 31 to 379 jobs; value added impacts averaged $6.0 million 

and ranged from $1.5 to $25.9 million. For a 40-MW power plant, 

output impacts of capital construction averaged $18.5 million and 

ranged from $3.4 to $78.7 million; employment impacts averaged 

159 jobs and ranged from 39 to 653 jobs; value added impacts 

averaged $9.2 million and ranged from $1.8 to $44.9 million. The 

large range of values is due to the fact that some counties have 

local sources for purchase of the major capital items, while in other 

cases these items must be imported from other regions, which 

represents a leakage from the local economy.

The economic impacts of annual operations in the first year for 

power plants in each county are summarized in table 6.6. Total 

output impacts for a 20-MW plant averaged $10.6 million and 

ranged from $2.8 to $14.4 million; employment impacts averaged 

170 jobs and ranged from 27 to 266 jobs; value added impacts 

averaged $6.3 million and ranged from $1.7 to $8.6 million. For 

the 40-MW plant, total output impacts of operations averaged 

$21.7 million and ranged from $4.6 to $31.5 million; employment 

impacts averaged 370 jobs and ranged from 43 to 629 jobs; 

value added impacts averaged $13.0 million and ranged from 

$2.8 to $18.9 million. These results for plant operations can be 

Table 6.6—Annual operating impacts (1st year) for 20- and 40-MW wood-fueled power plants in 

selected Southern U.S. counties 

 

County, State

20-MW plant 40-MW plant 

Output Employment 

Value 

added Output Employment 

Value 

added 

million $ no. jobs - - - - million $ - - - - - no. jobs million $ 

Lee, AL 12.40 210 7.63 25.25 447 15.69

Shelby, AL 11.35 125 7.28 24.33 276 15.76

Saline, AR 11.75 239 6.98 24.24 522 14.47

Union, AR 12.84 226 7.39 25.18 461 14.51

Alachua, FL 13.52 196 8.38 27.54 413 17.08

Clay, FL 11.73 182 7.10 25.30 420 15.35

Leon, FL 13.41 156 8.55 27.14 318 17.35

Nassau, FL 10.80 137 6.71 23.06 297 14.56

Santa Rosa, FL 12.47 147 7.70 25.94 307 16.18

Coweta, GA 9.51 160 5.52 18.41 331 10.71

Douglas, GA 7.96 75 4.46 14.21 130 7.84

Murray, GA 6.22 54 3.09 11.99 100 5.73

Union, GA 11.28 214 6.81 24.34 482 14.82

Laurel, KY 12.33 240 7.02 25.23 519 14.34

Trimble, KY 2.83 27 1.71 4.57 43 2.75

Livingston, LA 9.64 158 5.73 20.38 349 12.19

DeSoto, MS 8.27 155 5.18 16.70 356 10.83

Warren, MS 11.87 182 7.12 23.74 375 14.30

Buncombe, NC 12.84 242 7.59 26.65 546 15.77

Orange, NC 10.81 177 6.91 22.08 393 14.07

Le Flore, OK 8.22 85 3.88 15.78 155 7.38

Oconee, SC 10.76 220 5.98 23.16 508 12.86

Anderson, TN 11.51 216 6.94 24.96 510 15.08

Blount, TN 14.40 266 8.63 31.48 629 18.91

Sevier, TN 8.90 216 5.65 18.24 509 11.94

Montgomery, TX 11.32 154 6.79 21.73 314 13.03

Chesterfield, VA 13.08 187 7.84 28.46 437 17.07

Fluvanna, VA 9.56 218 5.51 20.42 501 11.89

Average 10.57 169.61 6.31 21.67 370.12 13.00
Chapter 6

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 75

considered as “permanent” impacts over the life of the plant. 

Again, the operating impacts varied widely among counties due to 

differences in the specific makeup of the local (county) economy, 

and in some cases, the absence of key sectors serving wood-fired 

power plant operations. If we consider the average of total output 

impacts for a 40-MW plant ($21.7 million) in comparison to the 

average direct expense for operations ($16.1 million), it would 

appear that there is an implicit multiplier effect of 1.35. In other 

words, the total impacts were 1.35 times the original expenditure. 

It was assumed in this analysis that the development of a woodfueled power plant would utilize the existing infrastructure for 

power distribution. 

Often it is important to understand the distribution of economic 

impacts across various sectors of the local economy. The estimated 

employment impacts of annual operations for a 40-MW power 

plant in each county are shown by major industry group in table 

6.7, according to the North American Industry Classification 

System. A large employment impact, averaging 226 jobs, or 61 

percent of total impacts, occurred in the agriculture and forestry 

sector, which supplies wood fuel to these plants, while there were 

also significant employment impacts in the sectors for professional 

services (27 jobs), retail trade (19 jobs), and government (22 jobs), 

reflecting the indirect and induced effects on the local economy. 

Table 6.7—Average employment impacts by industry group for annual 

operations (lst year) of 40-MW wood-fueled power plants in selected 

Southern U.S. counties 

Industry groupa

Average 

number 

jobs

Percent 

of total 

jobs

11 Agriculture, Forestry, Fishing and Hunting 226 61.2

21 Mining 0 0.0

22 Utilities 1 0.4

23 Construction 8 2.1

31–33 Manufacturing 2 0.6

42 Wholesale Trade 3 0.9

44–45 Retail Trade 19 5.2

48–49 Transportation and Warehousing 2 0.6

51 Information 1 0.3

52 Finance and Insurance 7 1.9

53 Real Estate and Rental and Leasing 5 1.4

54 Professional, Scientific and Technical Services 27 7.2

55 Management of Companies and Enterprises 1 0.4

56 Administrative and Support and Waste

 Management and Remediation Services 7 1.9

61 Educational Services 1 0.3

62 Health Care and Social Assistance 12 3.1

71 Arts, Entertainment, and Recreation 2 0.5

72 Accommodation and Food Services 12 3.2

81 Other Services (except Public Administration) 9 2.6

92 Public Administration 22 6.0

Total 370 100.0

a North American Industry Classification System. 
Economic Impact Analysis of Woody Biomass Energy Development

76 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

CONCLUSIONS

Potential economic impacts of wood-fueled power plants were 

examined for 28 counties in the Southern United States that were 

identified as highly suitable based on socioeconomic criteria. 

Construction and ongoing operations of wood-fueled power 

plants may have significant local economic impacts, but these 

impacts varied widely among selected counties, depending 

upon the particular makeup of the local economy. Utilization of 

wood fuel represents one of the largest expenditures for a power 

plant, and gives rise to large impacts in the local forestry and 

forestry services sectors. Other sectors of the local economy are 

also impacted through the indirect and induced effects of supply 

chain purchases and employee spending. Impacts of a 40-MW 

power plant are greater than for a 20-MW plant, although not in 

proportion to the power output, due to economies of scale. More 

precise estimates of economic impacts may be gained through 

site-specific engineering studies and customized regional inputoutput models.

REFERENCES

Johnson, K.P.; Kort, J.R. 2004. Redefinition of the BEA economic areas. 

Survey of Current Business. Nov.: 68–75.

Miller, R.E.; Blair, P.D. 1985. Input-output analysis: foundations and 

extensions. Englewood Cliffs, NJ: Prentice-Hall. 464 p. 

Minnesota IMPLAN Group (MIG), Inc. 1999. IMPLAN pro user’s guide, 

analysis guide, data guide. Version 2.0. Stillwater, MN: Minnesota Implan 

Group, Inc. 418 p. [Current pricing for IMPLAN regional data and other 

background information available at http://www.implan.com.]

Pugh, Scott A. 2004. RPA data wiz users guide. Version 1.0. GTR–NC–242. St. 

Paul, MN: U.S. Department of Agriculture Forest Service, North Central 

Research Station. 135 p.

Quaak, P.; Knoef, H.; Stassen, H. 1999. Energy from biomass: a review of 

combustion and gasification technologies. World Bank Tech. Pap. 422. 

Energy series. World Bank, NY. 99 p. 

Stewart, S.; Radeloff, V.; Hammer, R. [and others]. 2005. Mapping the 

wildland urban interface and projecting its growth to 2030. Misc. 

publication. Evanston, IL: U.S. Department of Agriculture Forest Service, 

North Central Research Station. 38 p.

U.S. Department of Commerce, Bureau of Economic Analysis. 2004. 

Personal income statistics for United States counties. http://www.bea.

doc.gov. [Date accessed: March 8, 2005].

U.S. Department of Commerce, Census Bureau. 2004. Annual benchmark 

report for retail trade and food services: January 1992 through February 

2004. Current Bus. Rep. BR/03–A. Washington, DC. 98 p. 

U.S. Department of Commerce, Census Bureau. 2004. Estimates of current 

population for U.S. counties. http://www.census.gov/popest/estimates.

php. [Date accessed: March 8, 2005].

U.S. Department of Energy, Energy Information Administration. 2004. U.S. 

electric generation. EIA 860 and EIA–906/920 Rep. Washington, DC. 

[Not paged].
Chapter 6

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 77

INPUT-OUTPUT ANALYSIS

Economic impact analysis is typically done using an analytical 

procedure known as input-output (I–O) analysis, which quantifies 

the structural relationships and interactions between industry 

sectors, households, and governments within a local economy 

(Miller and Blair 1985). I–O models are constructed from a 

transactions table that reflects the value of goods and services 

exchanged between all sectors of the economy in a 1-year base 

period. 

A simple example of a transactions table for a local economy is 

shown in table A.6.1 for an economy with four major industry 

sectors (agriculture, manufacturing, mining, and trade). In this 

example, the agricultural sector has total output of 39 units, of 

which 30 are sold to other producing industries as intermediate 

inputs, including 12 to other components of the agricultural 

sector, 2 to mining, 10 to manufacturing, and 6 to trade, then the 

remaining 9 are sold to final consumers. To produce its output, 

the agricultural sector makes purchases from other parts of the 

agricultural sector (12) and from each of the other producing 

industries, including 5 from mining, 5 from manufacturing, 2 from 

trade, and 7 from services, and 8 are value added inputs for profits, 

indirect business taxes, and payments to households. 

Changes in final demand, including local consumption and 

exports cause producing industries to respond accordingly to 

meet this change in demand. The value added section of the 

transaction table shows how each sector is linked to household 

income in the local area, and the household component of 

final demand reflect how each sector is impacted by local 

household spending. Producing industries in the economy are 

each listed twice in the transactions table, as both sellers and 

buyers of commodities. Rows in the table reflect the sales of 

output by each producing industry, including intermediate 

sales to other industries or institutions, and to final consumers 

such as households, government, and exports. Columns in the 

table reflect purchases by each producing industry from other 

industries, as well as value added inputs for payments to workers, 

taxes, owner profits, and imports. The table is balanced such 

that the total output of each producing industry equals the 

total value of purchases by that industry. Values are expressed in 

dollars or millions of dollars. In some formulations of I–O models, 

households may be shown as a producing industry that sells 

services (labor) and purchases inputs (consumption) in order 

to capture the effects of spending associated with changes in 

household earnings. An elaboration of the I–O model, known as 

social accounting matrices (SAM), enables the model to capture 

the effects of inventory change, capital investments, and transfer 

payments for nonearned income such as pensions and welfare. 

The linkages inherent in an I–O or SAM model are represented by 

economic multipliers that measure the total impact of a change 

in one or more industries on all other industries within the local 

economy (Miller and Blair 1985). Multipliers are derived from the 

transactions table using matrix mathematical procedures. An 

increase or decrease in output or employment within a specified 

Table A.6.1—An example transactions table for an input-output model of a local economy 

Selling industries 

Purchasing industries Final demand

Agriculture Mining Manufacturing Trade Services Households Government Exports Total

 Agriculture 

Mining 

Manufacturing 

Trade 

 Services 

12 2 10 6 0 1 1 7 39

5 2 20 0 0 0 2 11 40

5 3 6 20 5 9 10 40 98

2 3 2 1 5 25 10 5 53

7 10 30 2 10 18 10 0 87

Value added

Labor earnings 

Profits 

Imports 

5 14 20 12 35 75

1 2 3 4 10 20

1 2 3 4 22 32

Total 39 40 98 53 87 53 33 63 684

Note: value added components do not apply to final demand. 

Appendix: Input-Output Analysis and 

IMPLAN Software/Databases for Economic Impact Analysis

Chapter 6
Economic Impact Analysis of Woody Biomass Energy Development

78 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

industry is said to have a “multiplier effect” in the local economy. 

For a given industry, the size of the multiplier depends on the 

size of the economy and the degree of economic integration 

among regional businesses, and the level of sales outside the local 

region or exports. Firms that purchase more local inputs have 

higher multipliers as do firms with greater external sales. For each 

industry, multipliers estimate three components of total change 

within the local area: direct, indirect, and induced effects. Direct 

effects represent the initial change in the industry in question. 

Indirect effects represent changes in interindustry transactions 

as supplying industries respond to changes in demands from 

the directly affected industries. Induced effects reflect changes 

in local spending that result from income changes in the directly 

and indirectly affected industry sectors. Total effects multipliers 

usually range from 1.5 to 2.5, meaning that there will be a total 

change of 1.5 to 2.5 times the original direct change. IMPLAN 

multipliers are available for all of the basic impact measures, 

including output, employment, value added, labor income, 

employee compensation, other property income, and indirect 

business taxes. Output multipliers relate the changes in sales to 

final demand by one industry to total changes in output (gross 

sales) by all industries within the local area. Income multipliers 

relate the change in direct income to changes in total income 

or to changes in output within the local economy. Employment 

multipliers relate changes in direct employment or output to total 

employment effects, and may be stated either as a ratio of total to 

direct employment, or as a number of jobs per million dollars of 

output change. Value added multipliers are interpreted the same 

as income and employment multipliers; they relate changes in 

value added in the industry experiencing the direct effect to total 

changes in value added for the entire local economy.

I–O and SAM models have a number of standard assumptions and 

limitations that should be recognized. These models are fixed in 

their parameters, with constant technical relationships between 

industry sectors and constant prices or relationships between 

quantity and value. This means that changes in market prices 

and substitution of inputs or technologies are not allowed. Also, 

there are no capacity constraints to any shocks imposed to the 

system, so very large changes can lead to estimated impacts that 

unrealistically exceed local industry capacity. 

IMPLAN SOFTWARE AND DATABASES

IMPLAN is a proprietary computer software package and 

associated databases that enable the construction of regional I–O 

models for any area of the United States. IMPLAN is an acronym 

for impact analyses for planning. The computer program was 

originally developed by the Forest Service in cooperation with the 

Federal Emergency Management Agency and the U.S. Department 

of the Interior, Bureau of Land Management, to assist in land and 

resource management planning. Since 1993, the IMPLAN system 

has been developed under exclusive rights by the Minnesota 

IMPLAN Group, Inc., which licenses and distributes the software 

to users. IMPLAN has become the standard tool of economic 

impact analysis in the United States, with hundreds of licensed 

users, including universities, government agencies, and private 

companies. 

The economic data for IMPLAN is based on the system of national 

accounts for the United States, including information collected 

by the U.S. Department of Commerce, the U.S. Bureau of Labor 

Statistics, and other Federal and State Government Agencies. 

Data are compiled for 509 distinct producing industry sectors 

of the national economy defined according the North American 

Industrial Classification System (NAICS) based upon the primary 

commodity or service produced. Since 2001, the NAICS has 

supplanted the previous Standard Industrial Classification system 

in order to harmonize the economic statistics for the United 

States, Canada, and Mexico, as required under the North American 

Free Trade Agreement. Industry data incorporated in the model 

includes output, value added, employment, wages and business 

taxes paid, inputs purchased from other sectors, imports and 

exports, final demand by households and government, capital 

investment, business inventories, marketing margins, and inflation 

factors (deflators). The technological relationships between 

industry sectors reflect the benchmark I–O tables of the national 

economy, which are updated every 5 years based on the economic 

census conducted by the U.S. Census Bureau. State and countylevel data on employment, income, and population are the basis 

for IMPLAN I–O tables for local areas. Regional datasets for IMPLAN 

are updated annually for all counties in the United States. These 

data enable construction of I–O models for individual counties or 

for larger geographic areas such as clusters of contiguous counties 

or States. The regional datasets are purchased separately. IMPLAN 

software, data, and training are relatively inexpensive, making this 

system affordable for most organizations. Further technical details 

are provided in the IMPLAN User’s Guide (Minnesota IMPLAN 

Group, Inc. 1999) and Web site (www.implan.com).

Economic impact analysis with the IMPLAN software is conducted 

by specifying changes in the value of output or employment for 

particular sectors. Output and employment are interchangeable, 

and a change in one measure implies a change in the other 

according to the output per employee ratio. It does not matter 

whether the change is positive or negative; in either case the same 

multipliers are invoked. Values in IMPLAN may have a specified 

percentage of the expenditure that applies locally, or optionally, 

the local share may correspond to the regional purchase 

coefficient for the given industry sector, which represents the 

average share of inputs of a given commodity that are purchased 

from local sources. Any share < 100 percent means that the impact 

will be reduced because a portion of the value is lost as a “leakage” 

from the local economy. 

Economic Impact Analysis of Woody Biomass Energy Development
Chapter 6

Wood to Energy: Using Southern Interface Fuels for Bioenergy • 79

Values for commodities in IMPLAN are stated in producer prices, 

i.e., the prices of goods at the factory or production point. For 

manufactured goods, the price paid by final consumers equals 

the producer price plus margins that accrue to the wholesale, 

retail, and transportation sectors. IMPLAN contains information 

on typical margins for many different sectors, which may 

be optionally used to more accurately capture the effects of 

marketing chains. For service businesses, such as restaurants or 

hotels, the producer and purchaser prices are equivalent. For 

impact analysis of retail businesses, it is important to include 

only the gross margin on sales as a measure of output change, 

since most manufacture goods purchased at retail by consumers 

are produced outside the local area. Typical gross margins are 

available for broad types of retail establishments from the U.S. 

Census Bureau. 

IMPLAN models are constructed for a specific base year. Impact 

events specified for any other year must be deflated to express 

in model-year monetary terms, in order to maintain the proper 

relationships between employment and output values. The 

software contains deflator factors for each specific industry and 

year, which are automatically applied when impact events are 

specified. By default, impact analysis results are given in the 

model-year dollars, however, results may be reported in deflated 

terms for any particular year. 

IMPLAN models may be extensively modified and customized 

to take advantage of more specific information available about 

the study region or particular industries being examined. When 

used with all parameters set at default levels, IMPLAN models 

reflect prevailing national technical relationships and regional 

industry activity. In some cases, however, a particular industry 

may not be well represented by the national average technical 

coefficients. Some of the model information that an analyst may 

wish to modify includes industry output or employment, trade 

flows, commodity demand, industry production functions, or 

byproducts. For example, electric power plants that utilize wood 

fuels may differ significantly from the electric power industry at 

large. Also, one or two new industry sectors may be created to 

represent activities that are not well represented by any of the 

standard industry sectors. 

I–O models are constructed for an explicitly defined geographic 

area, so the definition of the region can be an important issue 

that may dramatically affect the results. IMPLAN offers flexibility 

to create regional economic models for individual counties, 

groups of counties, or States, depending upon the nature of the 

activity being evaluated. In general, the region should be defined 

large enough to encompass all of the local employment activity 

related to the affected industries. Typically, the region for impact 

analysis within a small- to medium-sized municipality would be 

the surrounding county, whereas an analysis of a large city or 

metro area would probably include a group of several counties. 

Also, the particular location of a facility may affect the definition 

of an appropriate regional model. For example, if a new plant is 

to be located near a county boundary, the neighboring county 

should probably be included in the regional model since it will be 

influenced by the facility. In cases where there is no compelling 

logical basis for definition of the region, the functional economic 

areas defined by the U.S. Department of Commerce, Bureau of 

Economic Analysis represent natural regions for economic impact 

analysis, which are based on analysis of worker commuting 

patterns reported in the decennial census of population and 

housing, together with other information such as newspaper 

readership (Johnson and Kort 2004). 

Chapter 6

Chapter 7

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 81

INTRODUCTION

Using wood from the wildland-urban interface (WUI) for fuel is 

advantageous because the close proximity of the forest to the 

facility reduces transportation costs for potential power users. 

In areas of rapid interface development, waste wood from land 

clearing can be a significant, though unsustainable, source of 

fuel. In areas of active forest management and extensive urban 

forests, sustainable sources of wood are available (see Langholtz 

and others, this publication). With careful planning and effective 

management, placing a woody biomass facility in the interface 

can be a reasonable decision. While there are significant concerns 

associated with using woody biomass, the planning process 

can be severely compromised if the public is not aware of the 

advantages and disadvantages of this resource. In the case of 

large-scale energy facilities or public utilities, local residents 

may expect to be involved in discussions about facility design. A 

number of studies (Upreti 2004, van der Hoorst 2002) cite public 

perception as playing a pivotal role in the success or failure of 

proposed biomass energy plants. Projects can stall, funds can be 

denied, and lawsuits can spell doom if the public does not support 

an initiative. With public support, however, projects can move 

forward in a spirit of cooperation and exploration. 

The likelihood and level of public support for utilizing woody 

biomass may be difficult to predict because support varies widely 

in the context of various biomass fuels and the preferences people 

have for management of nearby forests. The characteristics that 

affect proposals for using woody biomass for energy can be 

divided into three categories: perceptions of biomass in general, 

perceptions of forest sustainability, and perceptions of risk. 

The first three sections of this chapter review and interpret the 

available literature in the context of these three categories. The 

fourth section reports efforts to understand the public perceptions 

of using woody biomass in Gainesville, FL, where a pilot study of 

the Wood to Energy Outreach Program has been underway.

PUBLIC PERCEPTIONS OF BIOMASS

According to a series of polls conducted by utility companies 

across the United States from 1995 to 1997, residential customers 

favored renewable sources of electricity, with the majority of these 

customers stating a willingness to pay more per month on their 

electric bills for power generated from a renewable source (Bang 

and others 2000, Farhar 1999). 

Such news bodes well for proponents of biomass energy, except 

that respondents probably were not thinking about biomass when 

they completed the poll. These customers generally received the 

idea of biomass with less enthusiasm than other renewable energy 

sources like solar and wind. For example, when customers were 

asked about their preferred renewable energy options, solar, wind, 

and geothermal all received approval ratings above 60 percent, 

while biomass was much lower at 32 percent. Furthermore, more 

respondents (45 percent) were unwilling to bear additional costs 

associated with electricity produced from biomass than for wind 

(31 percent) or solar (35 percent). While a majority (53 percent) 

expressed a willingness to pay at least $4 more per month for 

biomass energy, this response is markedly lower than for other 

alternative energy sources (Farhar 1999). It is difficult to know if 

respondents are particularly displeased about utilizing biomass or 

are merely uninformed about this energy source.

Upreti (2004) attributes results like those reported by Farhar to 

a perceived advantage of energy sources that do not emit any 

pollutants, such as solar and wind, over those sources that are 

renewable but require a smokestack. Like conventional fuels, 

biomass energy involves combustion and, thus, prompts the 

perception that it creates air pollution. Consequently, it is deemed 

less attractive than other renewable energy sources. This might 

also explain the relative advantage that natural gas enjoys over 

other combustible energy sources—an energy source widely 

acclaimed to be “clean” is perceived to create no air pollution 

(Farhar 1999).

The concern over emissions is also apparent when analyzing 

perceptions of those who reside near a proposed facility. Key 

concerns from those residing near proposed facility sites included 

potential risk to health and safety, ecological concerns, potential 

for increased traffic, and the visual intrusion of the structure on the 

previously rural landscape (Upreti 2004). Some of these concerns 

are only relevant to facilities sited in rural areas and would not be 

as relevant to facilities in the WUI. These perceptions and concerns 

parallel those associated with other industrial developments that 

pose potential hazards (Khan 2004, Rosch and Kaltschmitt 1999). 

Perceived health risks also depend upon the fuel being burned 

(van den Hoogen and others 2002). Fuels perceived as dirty, e.g., 

chicken manure or sewer sludge, evoke much stronger concerns 

than do fuels perceived as cleaner, such as wood. Perceptions of 

Chapter 7

Public Perceptions of Using Wood for Fuel

Martha C. Monroe, Richard Plate, Lauren McDonell, and Annie Oxarart

Chapter 7
Public Perceptions of Using Wood for Fuel

82 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

the economic benefits of a biomass facility—primarily in the form 

of new jobs—may or may not be sufficient to sway local residents 

to favor such facilities; how people perceive the benefits depends 

on some of the other variables discussed throughout this review 

(Rosch and Kaltschmitt 1999, van der Horst 2005). 

Questions about the viability of using biomass are not limited 

to neighbors of bioenergy facilities. A number of environmental 

organizations have expressed similar concerns. While the U.S. 

Department of Energy, National Renewable Energy Laboratory 

regards biomass as an important tool for controlling greenhouse 

gas emissions and dependence on foreign oil (National Renewable 

Energy Laboratory 2009), environmental organizations are more 

wary of the potential problems of burning biomass. For example, 

the Natural Resource Defense Council (NRDC) views biomass as 

a beneficial fuel source that is renewable and can generate rural 

job opportunities, farmer revenue, and highly skilled positions, 

yet NRDC is concerned about the sustainability of the sources of 

wood and overall air quality, particularly for home heating (Natural 

Resource Defense Council 2003). 

One significant challenge to engaging the public in discussions 

about using wood for energy is that Americans know very little 

about energy in general. According to a 2002 national survey 

(National Environmental Education and Training Foundation 2002), 

only 12 percent of Americans can pass a basic quiz on energy 

knowledge. In addition, Americans overestimate their knowledge, 

believing that they have a lot or a fair amount of knowledge about 

energy. Misconceptions abound about the average gas mileage 

achieved by American vehicles, the causes of electricity shortages, 

the availability of new sources of energy, the sources of current 

energy, and nuclear waste storage (National Environmental 

Education and Training Foundation 2002). The lack of knowledge 

about basic energy issues makes it difficult for the American 

public to discuss options, learn about choices, and make good 

decisions about energy consumption and conservation, effectively 

maintaining our reliance on imported and domestic fossil fuels 

(National Environmental Education and Training Foundation 2002). 

One explanation for this energy illiteracy is our unfamiliarity with 

energy resources—our system provides relatively cheap electricity 

from distant sources with the flick of a switch. 

Knowledge about woody biomass energy is also lacking. For 

example, a mail survey of five counties in Florida revealed that 94 

percent of the respondents were familiar with the issue of global 

warming, but over 55 percent were unfamiliar with biomass as a 

source of energy and 68 percent had not heard of cofiring (Adams 

2003). Despite this lack of knowledge, they were willing to pay 

$5 to $20 more on each utility bill for cleaner energy technology 

that would reduce the effects of global warming. However, this 

willingness to contribute to cleaner energy does not translate into 

action. Over 50 percent of the respondents were not aware their 

utility provided such programs and < 6 percent were currently 

subscribed to them (Adams 2003). 

Even in Europe, where a number of biomass facilities are in 

operation, public awareness of the benefits from biomass 

is rather low and less is known about it than other forms 

of renewable energy (Rohracher and others 2004). Lack of 

knowledge in Europe, however, may not translate into a negative 

image about its use. Surveys in Austria show that attitudes 

toward biomass depend on who is promoting it, previous 

experience, and local politics (Rohracher and others 2004).

In general, the public does not perceive biomass to have the 

positive characteristics associated with noncombustible forms 

of renewable energy, and the public is concerned about impacts 

on air quality, health, traffic, and the environment. There is little 

evidence that woody biomass is perceived any differently. This 

literature review summarizes the general concerns associated with 

converting any biomass to energy, i.e., combustion or gasification. 

However, concerns about using woody biomass extend beyond 

the facility operations to the forests that are the source. The 

following section looks specifically at concerns regarding the 

sustainable management of woody biomass sources. 

PUBLIC PERCEPTIONS OF FOREST SUSTAINABILITY

Some woody biomass proposals have been rejected by local 

residents because of perceived negative environmental impacts 

(Upreti 2004). One factor that undermines citizen approval of 

using wood for energy is the perception that forests will be poorly 

managed or destroyed to supply the necessary quantity of fuel. 

Several national environmental advocacy groups, e.g., Natural 

Resource Defense Council (2003) and Greenpeace (2005), express 

support for biomass energy but emphasize that such support 

is contingent upon the availability of forests that are managed 

sustainably. Within some organizations, however, local opinions 

do not follow national policy. For example, the local conservation 

chair of the Suwannee-St. Johns Sierra Club promotes the use of 

woody biomass from all sustainably managed forests (Dickinson 

2005), even though the official national Sierra Club position 

opposes harvesting federally owned forests for electricity 

generation (Sierra Club 2007). One way to mitigate concerns about 

forest sustainability may be through forest certification systems 

that establish criteria for sustainable forest management. 

Concerns about forest management and the tendency to value 

preserved forests more than working forests may be an outgrowth 

of demographic change across the South. The South’s population 

is growing rapidly—over 11 million people were added 

(representing 11.5-percent growth) between 2000 and 2008 (U.S. 

Department of Commerce 2008). In addition, the South has been 

growing faster than other regions of the Nation, recording both 

the largest increase and the fastest growth rate between 2004 and 

2005 (U.S. Department of Commerce 2005). Some migrants from 

other regions of the country have brought wealth and a diversity 

of experience to their new communities in the South (Tarrant and 

others 2002). Urbanization has changed the way residents know 

and use nearby forests. 
Chapter 7

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 83

A telephone survey of 7,000 Americans suggests that the 

public supports ecosystem health, protecting watersheds, and 

nonconsumptive uses of national forests (Shields 2002). Policies 

that restrict timber and mineral extraction and support ecosystem 

protection are favored more by residents of the Eastern United 

States and metropolitan residents of the Western United States 

than by residents of nonmetropolitan Western States (Shields 

2002).This demonstrates that the trend toward ecosystem 

protection and away from timber production is also echoed in 

the South. 

In a 2001 telephone survey of 1,423 urban and rural residents of 

the 13 Southern States, the majority of respondents said that they 

believed the most important value of forests was clean air and the 

least important was wood production (Tarrant and others 2002). 

Respondents favored government funding for environmental 

protection and stricter environmental regulations, but did not 

extend these preservationist values to private forests (Tarrant and 

others 2002). 

Over the last 20 years, attitudes toward forest management 

have moved away from traditional timber production and 

toward protection, which could be a consequence of changing 

demographics, increased economic growth, greater technological 

innovations (Tarrant and others 2002), or a perceived scarcity of 

the resource. 

But in the South, unlike the West, the majority of forest land is 

privately owned—in some States, total private ownership is as 

high as 95 percent and nonindustrial private forest (NIPF) owners 

account for as much as 77 percent (U.S. Department of Agriculture 

2004). If NIPF landowners are interested in the potential financial 

gain that new markets associated with an increase in woody 

biomass would bring, they could help sway public opinion to 

support using woody biomass. But because NIPF landowner 

attitudes in some areas of the South are indistinguishable from 

their urban counterparts, these landowners may not be interested 

in marketing biomass for energy (Bliss and others 1997, Tarrant 

and others 2002). Most NIPF landowners currently manage their 

forests for both economic and noneconomic nontimber objectives 

(Bourke and Luloff 1994, Sinclair and Knuth 2000). Nevertheless, 

in WUI areas where the public wishes to maintain forest cover and 

direct development, it may be possible to obtain NIPF landowner 

support and approval for a woody biomass proposal that sustains 

private forests. Working with NIPF landowners may be an 

important element of a community woody biomass plan. 

In Finland, where the majority (62 percent) of forest land 

ownership is NIPF, results of a mail survey suggested that these 

landowners have positive attitudes about using wood for energy 

production. They felt that using wood for energy positively 

influenced the forest ecosystem, climate, employment, economic 

activity in rural areas, and recreational opportunities (Toivonen 

and others 2002). Of those who harvested wood for energy, over 

three-fourths of the respondents said they do so to improve the 

management of young stands, to enhance reforestation efforts, 

and to fuel their own homes. Those owners who did not harvest 

their forests were generally urban dwellers. 

In WUI areas, rural farms and working private forests are being 

converted into subdivisions and private parks. Residents of 

these areas may not perceive nearby green spaces as a resource 

that can be sustainably harvested, utilized, and renewed. New 

residents in the South may not be aware that pulp plantations 

have short rotations and, although recently harvested areas can 

look barren and bleak, they can become covered with vigorous 

green saplings in as little as 3 years from harvest. A new resident’s 

initial opposition to timber harvesting will likely need to be met 

with significant educational efforts explaining the benefits and 

operations of basic, sustainable forest management and the costs 

and benefits of using wood for energy. 

PERCEPTIONS OF RISK

Few studies have been conducted specifically on public 

perceptions of woody biomass, so we have gathered information 

about other types of biomass and other types of incinerators 

to describe how the public might respond to woody biomass 

proposals. The level of trust citizens have in the development and 

management of any proposed industrial facility is very important, 

and biomass energy plants are no exception (Sinclair and Lofstedt 

2001). For example, public trust in the facility owner and operator 

has been cited as a central factor in the acceptance of a biomass 

energy plant (Rosch and Kaltschmitt 1999). Failure of plant 

proposals in the United Kingdom has been attributed to questions 

about the validity of environmental impact statements made by 

developers in their planning applications (van der Hoorst and 

others 2002). Several types of trust are involved—a broad trust 

in the government or other large institutions and more specific 

trust in a particular developer or manager (Ibiatayo and Pijawka 

1999). A developer who is able to gain citizens’ trust on a personal 

level can overcome broad distrust in government and institutions. 

In some cases, partnerships involving government ownership 

combined with operation by a private company can serve to 

increase public trust in the operation as a whole (Ibiatayo 2002).

Research in this area is often approached in the context of risk 

communication, which emphasizes the need to engage the 

public in a dialogue aimed at understanding and addressing 

concerns. Establishing trust requires including the public early 

in the planning process for a proposed facility (Ibiatayo and 

Pijawka 1999, Kunreuther and others 1996, Rabe 1994, van der 

Horst and others 2002). Typically, the public is included only 

after a controversy has arisen, resulting in low levels of trust 

before the dialogue has even begun (Lofstedt 1999). When public 

involvement begins early in the planning process, as was the case 

in planning a hazardous waste facility in Alberta, Canada, the 

perceptions of the potential risks might be greatly reduced 

(Baxter and Greenlaw 2005). The perception of being “competent, 
Public Perceptions of Using Wood for Fuel

84 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

open, fair, concerned and reliable” can be established in the 

beginning and is vital to achieving and maintaining a high level 

of public trust throughout the process of establishing a facility 

(Lofstedt 1999).

Preexisting ideological beliefs are also key factors in the 

perception of a proposed facility. For example, residents of four 

towns involved in the process to site the Alberta hazardous waste 

facility varied in their perceptions of risk; their variations stemmed 

from different levels of comfort with uncertainty, identification of 

their communities as being primarily rural or urban, and feelings 

about being treated fairly (Baxter and Greenlaw 2005). 

Whether community members perceive their community as part 

of an expanding urban system or as an independent rural entity 

may be particularly important when siting a facility in the WUI. For 

example, residents of Barrhead in Alberta, Canada, a community 

that identified itself as closely connected to Edmonton (the 

closest urban center, approximately 45 miles away), welcomed 

light industry such as a waste facility. Conversely, residents from 

communities that identified with farming, fishing, and tourism 

activities viewed the facility as a threat to their way of life (Baxter 

and Greenlaw 2005).

Observations about siting hazardous waste facilities in the 

South provide important insights into community reactions. In 

Greensboro, NC, public trust and equity were significant factors 

and economic compensation was not, because the proposed 

incinerator offered few new jobs (Rabe 1994). Instead, the public 

desired “explicit guarantees against exploitation,” including 

enhanced safety measures and assurances that the facility would 

serve only local and intrastate needs (Rabe 1994).

Attitudes regarding a proposed hazardous waste incinerator 

in Putnam County, WV, suggest a strong desire for protection 

of public health (Hunter and Leyden 1995). Phone interviews 

identified six distinct categories of concerns regarding the 

proposed incinerator. First among these concerns was health and 

safety (26 percent of the respondents). In general, respondents 

were concerned about whether the development process would 

run smoothly and whether the incinerator operations would 

be managed safely. Concerns about aesthetics and property 

values (2 percent) and lack of knowledge (2 percent) received 

less attention from respondents. As in the other studies, public 

trust was a recurring theme, particularly concerning public 

safety and the development and operation of the facility. An 

important difference between this study and others, however, is 

that participants in this situation were probably considering the 

choice of having the hazardous waste incinerator or not having it. 

This is not often the case for energy facilities because communities 

that need additional energy will build some sort of facility. Woody 

biomass should be compared to other fuels, not compared to the 

option of no facility.

EXPLORING PUBLIC PERCEPTIONS 

IN GAINESVILLE, FL

How the public perceives woody biomass may influence whether 

the developer proposes a wood-to-energy facility. Judging 

by seemingly low public knowledge about energy (National 

Environmental Education and Training Foundation 2002), 

well-designed education and outreach activities could have a 

significant impact on public attitudes. The development of such 

materials should be based on an understanding of what the 

public knows, does not know, and cares about with regard to 

woody biomass (Jacobson and others 2006). The literature on 

biomass from Europe and on hazardous waste facilities from North 

America provides insights to what the public might think about 

woody biomass, but it is difficult to know if these insights will 

hold true in the context of public perceptions of woody biomass 

developments in the South. Before effective outreach programs 

can be created, more research is needed into local knowledge and 

attitudes toward woody biomass in the South. 

The Wood to Energy Outreach Program, developed in partnership 

between the University of Florida’s School of Forest Resources and 

Conservation and the Forest Service, explored several strategies 

for understanding public perceptions about woody biomass. 

The project ran an intensive pilot program in Gainesville, FL, of 

developing materials and outreach procedures, including woodto-energy community forums as models for community education. 

Wood to Energy Outreach Program leaders conducted interviews 

with residents of two communities (Oconee County, SC, and Clay 

County, FL) with the aim of learning more about perceptions and 

concerns the public across the South. The project also conducted 

interviews with city commissioners in Gainesville, FL. Responses 

suggest that attitudes in the South are similar to those expressed 

in the literature, with respondents expressing concerns about the 

effects of forest management and harvesting on forest health and 

sustainability and the impacts on air quality from wood-burning 

facilities. Responses from the city commissioners indicated 

concern about the sustainability of local wood resources, increased 

truck traffic, increased entry-level job opportunities, and forestry 

forecasts in an area that is rapidly converting rural land to urban 

land uses. Most respondents said that they believed that woody 

biomass could be an economical energy source if environmental 

concerns were first addressed (Monroe and others 2009b).

In another research project, a sample was randomly selected 

from the tax roll of single family and mobile home owners 

in Alachua County, FL, where Gainesville is located. Mobile 

home owners were included in the sample to obtain a broad 

demographic profile. The mailed survey included questions on: 

(1) general awareness about woody biomass; (2) trust of sources 

of information; (3) attitudes about using wood for energy, sources 

of wood, and forest management; and (4) the respondents’ 

demographics (Plate and others, in review). In general, survey 
Chapter 7

 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 85

results indicated that respondents (n = 302) were not very 

knowledgeable about using wood for energy and were confused 

about the relative advantages and disadvantages woody biomass 

when compared to fossil fuels, particularly about how the two 

energy sources affected global climate change. Respondents 

indicated that they were aware of their limited knowledge on 

the subject; nearly 50 percent responded to many knowledge 

questions by checking “I have no idea” and nearly 55 percent 

responded that they were “not at all knowledgeable” about the 

use of wood to generate electricity (Plate and others, in review). 

While using waste wood from urban tree trimming and forestry 

activities appealed to a majority of those responding to this 

survey, the most important concern they reported regarding 

woody biomass was the protection and sustainability of nearby 

forests. For these respondents, solar and wind continued to 

represent more desirable sources of energy than woody biomass. 

Respondents indicated that they were more curious and interested 

than skeptical or fearful when informed that their region could 

support a woody biomass power facility. They also expressed a 

lack of confidence in local government (40 percent indicated low 

confidence) but revealed a markedly different attitude about the 

possibility of a local utility company managing a wood-fueled 

power plant (49 percent indicated fairly or highly confident). (In 

this particular community, the local utility is owned by the City of 

Gainesville.)

As shown in table 7.1, respondents to the survey identified local 

foresters, environmental groups, and extension agents as the 

most reliable sources of information about woody biomass, and 

representatives of private industry as the least reliable sources. 

Finally, 53 percent of the respondents expressed a belief that 

the community could be fairly or highly influential in a proposed 

project, and 54 percent said they were fairly or highly interested in 

participating in the decisionmaking process (Plate and others, in 

review).

PROVIDING INFORMATION AND 

ENGAGING THE PUBLIC

The Alachua County survey suggested that respondents are not 

very knowledgeable about woody biomass and were particularly 

confused about the carbon-neutral nature of wood as an energy 

source. Because initial public responses to the Gainesville City 

Commission’s exploration of new sources of power drew criticism 

from citizens concerned about forest management and threats to 

forests under conservation protection, an outreach campaign on 

benefits of wood was not considered. People often do not respond 

well to persuasive messages that oppose their beliefs, and some 

people have been known to actively undermine policies they 

disagree with (Brehm and Brehm 1981). 

Because half of the survey respondents suggested a willingness 

to be involved, we created a nonconfrontational process that 

encouraged engagement through questions and discussion. The 

objectives of this outreach activity were to provide information, 

enable experts and members of the community to interact and 

learn from each other, and collect feedback about participants’ 

opinions, which could be shared with community decisionmakers 

(Monroe and others 2009a). 

The Wood to Energy Community Forum was a 30-minute or 

1-hour program, repeated several times at different locations over 

a 2-month period. It involved a 20- to 30-minute presentation 

by four or five experts who introduced their respective areas of 

expertise—forest management, the carbon cycle, technology, 

local supply of wood, and regional economic impact. Following 

the presentation, a forum facilitator encouraged the audience to 

ask questions of the experts. Participants completed a preforum 

and postforum survey about the forum. Attending 6 forums 

in November and December of 2006 were 172 community 

members from Gainesville, FL. Surveys were completed by 108 

of these participants. Survey results suggested that participants 

learned from the forum and appreciated the opportunity to voice 

concerns and ask questions of experts. Their answers indicated 

that the participants would feel positive about a proposal to build 

a biomass energy facility, if the facility’s design addressed their 

concerns (Monroe and others 2009a).

Our experience with the first community forum (a potentially 

hostile Sierra Club meeting) helped us revise our presentation, 

simplify our message, and focus more clearly on issues that lead to 

confusion. From our experience with the six forums, we offer the 

following advice to others who are planning community outreach 

activities:

• Simplify the information. Use graphics and photographs in 

the presentation, use analogies to explain concepts, and do 

not assume that people know much about energy, forest 

management, or economics. (Questions and comments from 

the audience helped us realize when we did and did not pitch 

the information to the appropriate level.)

Table 7.1—Level of trust for various sources to provide 

reliable information about a wood-to-energy program 

Source of information

Perceived reliability 

of informationa

Local forester 2.2

Environmental group 2.2

Extension agent 2.1

Local utility company 1.9

Local newspaper 1.8

Private industry 1.6

Chamber of Commerce 1.6

a

1 = Not at all reliable; 3 = Very reliable. 
Public Perceptions of Using Wood for Fuel

86 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

• People want information but can be overwhelmed by too 

much information. Aim for enough information to generate 

reasonable questions and leave plenty of time for audience 

interaction. (Survey respondents marked the opportunity to ask 

questions as one of the important benefits of the forum.)

• Focus discussion on the comparison of reasonable options for 

meeting energy needs, rather than the impact of building a new 

facility compared to not building one, i.e., currently existing 

power plants. (A new facility will always generate more concerns 

and expenses than not having a new facility, but if additional 

energy is needed, then comparing reasonable strategies for 

obtaining that energy should be the focus.)

• Create an atmosphere that welcomes multiple perspectives and 

does not assume that the experts have the answer. The attitude 

of the experts as they present information is critical; asking 

participants to complete a survey helps them share information 

with the experts and organizers. (Survey respondents also rated 

the ability to access experts and the facilitator as important 

elements of a forum.) 

• Work with existing community clubs and volunteer to hold a 

forum at one of their regularly scheduled meetings. This helps 

guarantee an audience and takes advantage of their publicity 

network, even though it may constrain the format or length of 

the forum. (Attendance at existing club meetings was much 

higher than at public forums we advertised.)

Strategies that enable organizers to compile feedback and convey 

citizen preferences to decisionmakers could be quite helpful in 

generating broad discussion and building trust. (We conducted 

pre- and postsurveys and shared the results with local city 

commissioners.)

Forums about energy sources in general can easily convey 

advantages and disadvantages about a number of different 

sources. A forum about only one source, e.g., wood, will risk the 

appearance of bias or advocacy. In such cases, it may be helpful to 

stress that there are many different strategies of using wood for 

energy and offer conflicting perspectives around these variations. 

(It was difficult to avoid promoting the use of wood for energy 

since that was the only topic of the forum. It would have been 

better to run a series of forums on energy, with wood being one 

of them.)

If people have little knowledge about woody biomass, it appears 

that they are satisfied with a “yes” or “no” answer to the simple 

question, “Should we use wood for energy?” As people learn more 

about the strategies for producing, hauling, and converting wood 

to energy, they are more likely to be interested in addressing the 

more insightful question, “What system best meets our needs 

for quality environment, community, and economy?” By taking 

time for broader issues associated with using wood for energy, 

people begin to consider related aspects, such as wood sources, 

harvesting, forest management, transportation, boiler technology, 

scale, and fuel type. By supporting public discussion of criteria for 

an acceptable local woody biomass system, outreach strategies 

could give local decisionmakers the information they need about 

community perceptions and preferences.

SUMMARY

Public understanding and acceptance of woody biomass facilities 

is essential for the expansion of this energy source in the southern 

WUI. Although a significant number of sawmills, pulpmills, and 

small facilities have used wood for years to produce heat and 

power, the technology is relatively unknown among the general 

public. Surveys suggest that the public knows very little about 

energy in general, and even less about using wood for energy.

Developing educational and outreach materials that provide 

useful information requires an understanding of public 

perceptions and concerns. This literature review and the pilot 

program results suggest the following themes:

• While people look favorably on renewable energy sources in 

general, they view biomass energy production as comparatively 

less attractive than other renewable energy sources due to its 

relative similarity to fossil fuels. They do not understand carbon 

neutrality and are concerned about air pollution.

• Individuals within the immediate area of a proposed biomass 

power plant express concerns similar to those of people who 

live near other types of industrial facilities. These concerns 

include personal health and safety, environmental impacts, 

aesthetics of the landscape, increased noise, and increased 

traffic. 

• The potential for mismanagement of forests that supply woody 

biomass is a very large public concern. To address the concern, 

it may be useful to develop guidelines that support sustainable 

forest operations as sources of woody biomass.

• Public trust in the developer and manager of the proposed 

bioenergy facility is a pivotal factor in how the public interprets 

the potential risks posed by a new facility. 

• Also playing important roles in public perception are how a 

community perceives the relationship between rural sources 

of wood and urban demands for energy, and how community 

members identify their community’s relationship to the WUI. 

• Outreach opportunities that translate information into language 

that can be understood by the general public, and that offer 

interaction with subject experts could build trust, foster 

understanding, and help increase public acceptance of some 

types of wood-to-energy facilities.

• The public perceives forest agencies, extension agents, and 

environmental organizations as more trustworthy than industry 

and government. 

In light of these observations, a successful outreach effort to 

educate local citizens and generate helpful discussion should 

explain why woody biomass is a renewable source of energy, 

distinguish woody biomass fuel from other energy sources, 
 Wood to Energy: Using Southern Interface Fuels for Bioenergy • 87

Chapter 7

and address forest management and sustainability. For projects 

that aim to engage the public in developing an acceptable 

proposal, outreach efforts should also provide early and open 

communication between bioenergy facility developer(s) and 

the public, demonstrate how the proposal addresses questions 

and concerns voiced by the public, foster relationships with 

community leaders and partners who can help to build public 

trust in the proposed development, and jointly develop indicators 

to chart progress as the facility begins operation.

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Wood to Energy: Using Southern Interface Fuels for Bioenergy • 89

Compiling Editors

Christie Staudhammer Assistant professor 

(Forest Biometrics)

University of Florida

School of Forest Resources 

and Conservation

349 Newins-Ziegler Hall 

P.O. Box 110410 

Gainesville, FL 32611-0410

352-846-3503

staudham@ufl.edu

L. Annie Hermansen-Báez Center manager/

technology transfer 

coordinator

U.S. Department of 

Agriculture Forest Service

Southern Research Station

InterfaceSouth

Building 164, Mowry Road

P.O. Box 110806

Gainesville, FL 32611

352-376-3271

ahermansen@fs.fed.us

Douglas R. Carter Professor (Forest 

Economics and 

Management)

University of Florida

School of Forest Resources 

and Conservation

357 Newins-Ziegler Hall 

P.O. Box 110410 

Gainesville, FL 32611-0410

352-846-0893

drcart@ufl.edu

Edward A. Macie Regional urban 

forester

Forest Service

U.S. Department of 

Agriculture

Region 8

1720 Peachtree Road 

Atlanta, GA 30309

404-347-1647

emacie@fs.fed.us

Authors

Chapter 1

Christie Staudhammer Assistant professor 

(Forest Biometrics)

University of Florida

School of Forest Resources 

and Conservation

349 Newins-Ziegler Hall 

P.O. Box 110410 

Gainesville, FL 32611-0410

352-846-3503

staudham@ufl.edu

Chapter 2 

Christie Staudhammer 

(lead author)

Assistant professor 

(Forest Biometrics)

University of Florida

School of Forest Resources 

and Conservation

349 Newins-Ziegler Hall 

P.O. Box 110410 

Gainesville, FL 32611-0410

352-846-3503

staudham@ufl.edu

Richard Schroeder President and 

founder

BioResource Management, 

Inc.

3520 NW 43rd Street 

Gainesville, FL 32606

352-377-8282 

rs@bio-resource.com

Brian Becker Ph.D. student University of Florida

School of Natural 

Resources and Environment

P.O. Box 110831 

Gainesville, FL 32611-0831

brbecker@ufl.edu

Matthew H. Langholtz Biomass consultant Oak Ridge National 

Laboratory

PO Box 2008 MS6422

Oak Ridge, TN 37831-6422

865-574-6520 

langholtzmh@ornl.gov

EDITORS AND AUTHORS

Editors and Authors
90 • Wood to Energy: Using Southern Interface Fuels for Bioenergy

Editors and Authors

Chapter 3

Richard Schroeder President and 

founder

BioResource Management, 

Inc.

3520 NW 43rd Street 

Gainesville, FL 32606

352-377-8282

rs@bio-resource.com

Chapter 4

Phil Badger 

(lead author)

Technical director U.S. Department of Energy

SSEB

Biomass State and Regional 

Partnership

3115 Northington Court

P.O. Box 26

Florence, AL 35630

256-740-5634 

pbadger@

bioenergyupdate.com 

Pratap 

Pullammanappallil

Assistant Professor University of 

Florida Agricultural 

and Biological Engineering

P.O. Box 110570

Gainesville, FL US 

32611-0570

352-392-1864

Chapter 5

Matthew H. Langholtz 

(lead author)

Biomass consultant Oak Ridge National 

Laboratory

PO Box 2008 MS6422

Oak Ridge, TN 37831-6422

865-574-6520

langholtzmh@ornl.gov

Douglas R. Carter Professor (Forest 

Economics and 

Management)

University of Florida

School of Forest Resources 

and Conservation

357 Newins-Ziegler Hall 

P.O. Box 110410 

Gainesville, FL 32611-0410

352-846-0893

drcart@ufl.edu

Richard Schroeder President and 

founder

BioResource Management, 

Inc.

3520 NW 43rd Street

Gainesville, FL 32606

352-377-8282

rs@bio-resource.com

Chapter 6

Alan W. Hodges Extension scientist University of Florida

Food and Economic 

Resources Department

1115 MCCB

P.O. Box 110240 IFAS

Gainesville, FL 32611-0240

352-392-1881 Ext. 312

awhodges@ufl.edu

Chapter 7

Martha C. Monroe 

(lead author)

Professor University of Florida

School of Forest Resources 

and Conservation

347 Newins-Zeigler Hall

P.O. Box 110410

Gainesville, FL 32611

352-846-0878

mcmonroe@ufl.edu

Richard Plate Graduate Student University of Florida

School of Natural Resources 

and Environment

P.O. Box 116455 

Gainesville, FL 32611

richarp@ufl.edu

Lauren McDonell Former wood to 

energy coordinator

University of Florida

School of Forest Resources 

and Conservation

Newins-Zeigler Hall

P.O. Box 110410

Gainesville, FL 32611

970-884-3182

mcdonell@ufl.edu

Annie Oxarart Wood to energy 

coordinator

University of Florida

School of Forest Resources 

and Conservation

Newins-Zeigler Hall

P.O. Box 110410

Gainesville, FL 32611

352-846-0144

oxarart@ufl.edu
Staudhammer, C.; Hermansen-Báez, L.A.; Carter, D.; Macie, E.A., eds. 2011. Wood to energy: 

using southern interface fuels for bioenergy. Gen. Tech. Rep. SRS-132. Asheville, NC: 

Department of Agriculture Forest Service, Southern Research Station. 90 p.

This publications aims to increase awareness of potential uses for woody biomass in the southern 

wildland-urban interface (WUI) and to disseminate knowledge about putting bioenergy 

production systems in place, while addressing issues unique to WUI areas. Chapter topics include 

woody biomass sources in the wildland-urban interface; harvesting, preprocessing and delivery 

of woody biomass in the wildland-urban interface; biomass conversion to energy and fuels; the 

economic availability of woody biomass; economic impact analysis of woody biomass energy 

development; and public perceptions of using wood for fuel.

Keywords: Bioenergy, biomass fuel, wildland-urban interface, woody biomass, wood-to-energy.
The Forest Service, United States Department 

of Agriculture (USDA), is dedicated to the 

principle of multiple use management of 

the Nation’s forest resources for sustained 

yields of wood, water, forage, wildlife, and 

recreation. Through forestry research, 

cooperation with the States and private forest owners, 

and management of the National Forests and National 

Grasslands, it strives—as directed by Congress—to provide 

increasingly greater service to a growing Nation.

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programs.) Persons with disabilities who require alternative 

means for communication of program information (Braille, 

large print, audiotape, etc.) should contact USDA’s TARGET 

Center at (202) 720-2600 (voice and TDD).

To file a complaint of discrimination, write to USDA, 

Director, Office of Civil Rights, 1400 Independence 

Avenue, SW, Washington, D.C. 20250-9410, or call (800) 

795-3272 (voice) or (202) 720-6382 (TDD). USDA is an equal 

opportunity provider and employer.

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