ENERGY FROM
BIOMASS AND
WASTES XII
Edited by
Donald L. Klass
Institute of Gas Technology, Chicago, Illinois, U.S.A.
INSTITUTE OF GAS TECHNOLOGY
CHICAGO
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PANEL DISCUSSION ON THE RELATIVE MERITS OF WOODGRASS AND SRIC L. L. Wright Environmental Sciences Division Oak Ridge National Laboratory Oak Ridge, TN 37831-6352 and
D. S. DeBell, C. H. Strauss, W. A. Geyer,
L. Sennerby-Forsse, L. zsuffa, and Edwin White
ABSTRACT
A debate on the relative merits of woodgrass versus
short-rotation intensive culture (SRIC) as alternative
biomass-energy-feedstock production systems was organized
via two vehicles: (1) a panel discussion that was held
immediately following the presentation of papers in the
woodgrass and SRIC sessions of the IGT conference and (2) a
questionnaire prepared after the meeting to obtain
informed, written opinions from the panelists on the
relative merits of woodgrass and SRIC.
Highlights of the
panel discussion are briefly summarized.
The major portion
of the text consists of four questions prepared by Lynn
Wright and the responses by the coauthors of this paper.
The coauthors represent varying opinions on the relative
merits of woodgrass and SRIC.
The summary presents the
first author's opinion after consideration of all
responses.
261
PANEL DISCUSSION ON THE RELATIVE MERITS OF
WOODGRASS AND SRIC
INTRODUCTION
After 10 years of research on biomass production,
researchers are convinced that the intensive culture of
hardwood trees is a desirable strategy for producing
biomass-energy feedstocks. However, there are differences
of opinion regarding the characteristics of the production
systems that will produce the "best" energy feedstock.
These different opinions often result because "best" is not
clearly defined.
Nevertheless, three approaches are being
evaluated for wood-energy feedstock production. The
approaches differ most significantly in planting density,
rotation length, and size of harvested product. Chemical
composition of the harvested product may differ also.
Advocates and characteristics of the three production
systems are briefly described in the following paragraphs.
The managers of the Short Rotation Woody crops
Program, a research program supported by the u.s.
Department of Energy, recently suggested that the highest
productivity could be obtained for the lowest cost by
employing improved clones, intensive site preparation, weed
control, some use of fertilizer, planting densities of
2, 500 to 4, 000 trees per hectare, and harvest intervals of
5 to 8 years (Ranney et al. 1987). This recommendation was
based on analysis of research results from experiments
conducted at densities ranging from 1, 000 to 200, 000 trees
per hectare. This production system is being used
commercially for energy and fiber production by industries
such as James River Corporation of Nevada, in Oregon; Scott
Paper Company, in Alabama; and Domtar, in canada. Such a
system results in trees with breast height diameters (DBH)
of 8 to 20 em at harvest age. Recommended plantation
regeneration options include coppice growth or replanting
with genetically improved materials. This production
system is generally referred to as short-rotation intensive
culture (SRIC).
A second approach was introduced as "woodgrass" by
Joe Dula, a nursery operator in the Pacific Northwest (Dula
1984). The production system described by Dula is
characterized by the establishment of 50, 000 to 200, 000
trees per hectare with annual harvest as long as coppice
regrowth is viable. It also employs selected clones,
intensive site preparation, some weed control, and use of
fertilizers. The system produces succulent, small-diameter
stems (1 to 3 em) with a high nitrogen content. This
production system is similar to cutting production systems
used at nurseries. The system is not yet in commercial use
for energy or fiber production because it is in a
relatively early stage of research. Poplars are being
seriously tested for woodgrass systems, but willows appear
262
receiving the greatest support from the Gas Research
Institute because the quality of the wood produced appears
to be well suited for conversion to methane.
A third production system being advocated and tested
primarily in Europe (Great Britain, Sweden, and Finland)
contains elements of both the SRIC and woodgrass
approaches. This system is most commonly referred to as a
"short-rotation coppice system" or "coppice system." It
differs primarily from SRIC as practiced in the United
states in that the emphasis is on willows, and that the
single-stemmed establishment rotation incorporated in SRIC
is bypassed in coppice systems by cutting newly established
trees at the end of the first growing season. Mitchell
( 1987) recently stated that 3- to 5-year coppice rotations
were attracting the most interest in Europe. This harvest
interval corresponds to initial planting densities of 10 to
20, 000 sterns per hectare, and stern size at harvest is
likely to have a DBH of 2 to 6 em. This production system
also incorporates extensive site preparation, good weed
control, and fertilization. This system and SRIC systems
will be discussed in contrast to woodgrass systems.
METHODS
During the 1988 Conference on Energy from Biomass and
Wastes XII, sponsored by the Institute of Gas Technology
(IGT), a panel discussion was organized by Don Klass,
Conference Chairman, to stimulate discussion of the
relative merits of the two production systems that are
being most seriously tested in the United states. All
presenters in the SRIC and woodgrass sessions of the
conference were requested to serve as panelists. The
panelists represented ongoing research on all three biomass
production systems described in the introduction.
Qualifications of the panelists who participated in
authoring this paper are described in the following
paragraph.
Dr. D. s. DeBell, a silviculturist with the USDA
Forest Service, has studied poplars and alders in SRIC
systems for almost 20 years but has recently established
woodgrass and SRIC trials using two extremely fast-growing
poplar clones. Dr. c. H. Strauss, an economist at The
Pennsylvania State University, has worked more than 10
years with a team of scientists evaluating the
productivity, wood quality, and economics of growing SRIC
poplars on a 4-year rotation strategy.
Dr. W. A. Geyer, a
silviculturist at Kansas State University, has evaluated
the production of several hardwood species under both SRIC
and woodgrass production strategies for over 20 years. Dr.
L. Sennerby-Forsse, a silviculturist associated with the
management of Sweden's Energy Forestry Project, has studied
willows for over 10 years in short-rotation coppice
systems. Edwin White, a professor of Forest Soil Science
263
in the College of Environmental science and Forestry at the
state University of New York, with 10 to 15 years
experience in evaluating SRIC systems, is currently
evaluating woodgrass willow as a possible methane
feedstock.
PANEL DISCUSSION
Don Klass started questioning the panel by asking which biomass-energy-feedstock production system was " best." Each panelist was given an opportunity to make a statement. Questions were also accepted from members of the audience. The highlights of this discussion are summarized as follows: The question concerning which system was " best" was
not directly answered by most of the panelists. Many of
the panelists• introductory comments were hedged by the
fact that the criteria for determining " best" was not
clearly defined. There appeared to be a consensus that the
criteria by which the three approaches must ultimately be
evaluated should include wood-energy qualities as well as
biomass yields and production costs. Many factors could
affect wood-energy qualities, including the species and
clones chosen, age, spacing, and amount of fertilizer
applied. Further comments suggested that it is difficult
to determine the " best" biomass-energy feedstock without .
knowing the end product (e.g., methanol, ethanol, methane,
or heat) and the preferred conversion pathway (e.g.,
thermochemical, biochemical, gasification, anaerobic
digestion, or direct combustion). One contributor from the
audience indicated that the conventional forest products
industry would not readily accept the concept of intensive
culture (woodgrass or SRIC) unless it was emphasized that
conventional wood uses (e.g., pulp) were viable products of
these culture strategies.
The panelists did not refute the opinions of other
members of the panel; the positive features of each
biomass-production strategy were stressed. Proponents of
SRIC offered arguments that the SRIC strategy is close to
eccnomic viability now and is a homogenous product suitable
for a wide number of conversion pathways. Proponents of
woodgrass argued that it is a preferable feedstock for
specific energy conversion pathways, it can alternatively
serve as animal food, and that current economic drawbacks
can be overcome with further research and development.
An audience participant requested the panelists to
address the qUestion of how long high yields can be
sustained without replanting in SRIC and woodgrass systems.
Answers by the panelists included the following comments.
SRIC plantations are anticipated to have at least a 20-year
lifetime at harvest intervals of 4 to 5 years. Harvest
intervals of 5 to 10 years in more widely spaced SRIC
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plantations would likely result in an even longer period of
sustained high yields. It is anticipated that more densely
spaced poplar woodgrass plantations are likely to suffer
reduced yields in less than 10 years, with selected willows
sustaining yields over a longer period.
The cultural
amendments used, as well as the species andjor clones
chosen, can make a considerable difference in survival and
sustainability of yields under any of the strategies. one
panelist disagreed on the importance of the issue of
sustainability, suggesting instead that it may be
economically desirable to replant with new genotypes on a
relatively frequent basis to avoid pest or disease problems
or to take advantage of faster growth rates.
Don Klass summarized the discussions and concluded
that further research on both SRIC and woodgrass should
continue in order to keep all options open for optimizing
the best wood energy feedstock for each conversion pathway.
WRITTEN RESPONSES
Although the panel discussion came to the logical
conclusion stated above, it did not completely serve its
initial intent of providing a straightforward comparison of
the relative merits of the different energy-feedstock
production systems. Therefore, each of the panelists was
asked to prepare brief written answers to a specific set of
questions designed to elucidate current opinions in the
research community about SRIC and woodgrass. Not all
panelists responded, and thus one additional expert,
Dr. Louis zsuffa, who participated in the conference
discussions, was asked to contribute to this paper.
Dr. Zsuffa, University of Toronto, Ontario, canada, is a
geneticist with over 20 years experience in the genetic
improvement and testing of both poplars and willows in SRIC
systems and recent experience in testing new clones for
woodgrass systems. Most respondents have had research
experience with both SRIC (U.S. or European versions) and
woodgrass systems. The following paragraphs present the
questions and the answers received.
Question 1 (Wood Energy Qualities):
Please briefly
describe your perception of the wood qualiti3s or
characteristics of the species and cultural
technique (s) with which you are most familiar and the
energy conversion pathway (s) or other uses for which
it would be best suited.
Question 2 (Realistic Current Yields):
Please
briefly discuss your scientific judgment or knowledge
of the harvestable yields that can be obtained with
currently available clones and cultural techniques on
large acreage, good-quality sites using woodgrass
265
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.,
'
andjor SRIC (U.S. or European) approaches. Express
the yields in terms of whole-tree aboveground,
leafless dry weights on a per hectare basis. If the
leaves are to be used for energy production, express
the dry weight of leaves separately.
Question 3 {Recommended Cultural Strategy):
Please
express an opinion on which cultural strategy would
be most economical for producing energy feedstocks
given clones and techniques commercially available
today. Provide background information for your
opinion, if possible.
Question 4 (Research Needed):
Please discuss the
research avenues and breakthroughs needed to ensure
that either woodgrass or SRIC (U.S. or European) can
provide large amounts of low-cost biomass feedstock
for energy production in the future.
Responses to the above questions from researchers
involved in SRIC and/or woodgrass research are provided in
their entirety on the following pages. In both the
questions and the responses, no effort is made to
differentiate between the European and u.s. approaches to
SRIC because the differences in wood quality are not that
great. No editorial changes were made without the consent
of the author. Each author is identified by name at the
beginning of each response.
Question 1:
Wood Energy Qualities
Dean DeBell:
Woody biomass characteristics vary by species
and cultural treatments, but there are some trends with age
and plant size that may significantly affect choices among
alternative woodgrass and SRIC systems. In general, trees
of younger age and smaller size (e.g., woodgrass systems)
have higher contents of bark, extractives, nutrients, and
moisture and a lower content of cellulose than an equal
biomass from older, larger trees (e.g., SRIC system). The
smaller, younger trees also tend to have lower specific
gravity; thus, a larger volume of woody material must be
processed to provide the same biomass,
The relative value
of such differences will depend on conversion technology.
Because the woodgrass system entails higher production
costs and results in lower yields, considerable economic or
environmental benefits must be associated with such
differences in biomass traits for woodgrass to compete
effectively with biomass produced by SRIC systems.
Biomass research at Penn State has
Charles H. Strauss:
involved one hybrid poplar clone grown under four
strategies (control, fertilization, irrigation, and
fertilization-irrigation) and on two different sites. A
spacing of 0. 6 m by 0.8 m wa::- ''Sed for the 4-year rotation
system, requiring 21,000 cuttings per hectare. Evaluations
of the gross heat of combustion for Populus were 19.4 GJ
266
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1
Additional wood and bark evaluations were
Mg. (0D).
completed for constituent, chemical, and energy analyses of
the materials.
Overall, the harvested Populus proved to be
a homogeneous product, well suited to the feedstock
requirements of ethanol conversion processes.
wayne Geyer:
The conversion technology that I am most
familiar with is air gasification of wood chips with a
downdraft gasifier.
For this and all other conversion
processes other than anaerobic digestion, the following
characteristics are desired.
*
Low moisture in trees (field) to reduce curing time.
*
Few but heavy branches on trees to facilitate chipping. *
Wood chips that don't leave strips (stringers).
*
Low rate of deterioration in field or chip pile.
Lisa Sennerby-Forsse:
In Sweden the main use of SRIC
biomass is meant to be the direct combustion of wood chips
in medium-scaled power plants for heating of houses.
Important characteristics of the biomass used this way are
the moisture content at harvesting (wintertime) , the wood
density which influences the yield and the energy content.
The energy content has not been shown to vary a lot between
the willows; however, one might expect the rotation time,
and thereby, indirectly, the amount of bark on the sterns,
to have some influence on the heat value of the total
Also the chemical composition of the bark can
biomass.
vary and may affect the heat value.
Other important
characteristics for a rationally managed energy plantation
is gross morphology of the plants; that is, they should be
readily harvestable with an upright stern formation and not
By prolonging the rotation time, many of the
too branchy.
willows used today would be suitable raw material for
industrial use such as pulp and fiberboard.
There is a
strong correlation between fiber length and overall wood
quality and age in shrubby willows--the former increasing
with age up to about 10 to 12 years.
Both willows and poplars have similar
Louis Zsuffa:
properties in a general sense when grown in SRIC systems of
3- to 10-year rotations.
Both can be suitable for direct
combustion and other conversion processes as well as for
pulp and fiberboard.
Woodgrass suits the production of
methane through anaerobic digestion processes better than
SRIC wood.
The more green material and more nitrogen in
the sterns, the better the gas yields.
There is much
variation within both poplars and willows with respect to
these characteristics.
Edwin White:
Specific wood biomass quality varies by
species and cultural systems although, in general, it
appears that at least willows and poplars have similar
properties when produced in SRIC systems of 2- to 10-year
rotations.
Rotation lengths and spacings and cultural
operations such as fertilization and clonal selections can
be utilized to influence biomass quality; for example,
percentage of foliage, bark, branches, and stern wood;
267
nutrient concentrations; and biomass yields.
Wood quality
variation in both willows and poplars provide selection
criteria for breeding programs to "improve" biomass
qualities for specific uses.
Question 2:
Realistic
current
Yields
Dean DeBell:
No published data exist on SRIC or woodgrass
yields obtained over large acreages, and only limited yield
·data are available from reasonably large plots replicated
in an adequate experimental design.
Most so-called "yield"
data from SRIC and woodgrass experiments should be regarded
as indicative of relative performance of various genotypes
or cultural treatments--not as solid evidence of yields
obtainable in actual operations.
If the best current
technology and genotypes were used on good sites in the
temperate zone, I would estimate harvestable yields of
aboveground, leafless dry biomass over large acreages at 8
1
1
to 12 MG (OD) ha" year" for woodgrass cut on an annual
1
1
year" for SRIC plantings
basis and 15 to 20 MG (OD) ha·
cut on rotations of 4+ years.
Charles Strauss:
Average annual production from the first
two (4-year, SRIC) rotations on the nonfertilizer
1
1
strategies was 8. 9 MG (OD) ha" year" and on the fertilized
1
1
strategies 10.9 Mg (OD) ha" year" •
output from the second
rotation was about 12% greater than from the first
rotation.
Weed control was a necessary prerequisite in the
first rotation for securing adequate yields.
Wayne Geyer:
Employing the premise that yields in large
plantings will be 3/4 that of small research plots at
5 years with 1.6 m spacing, SRIC planting yields in the
Eastern Great Plains can be expected as follows:
*
Eastern Kansas upland loam sites--black locust,
silver maple, cottonwood, and Siberian elm, 5 Mg (OD)
1
ha" year· ;
*
Eastern Kansas alluvial loam sites--black locust, 1
1
cottonwood, and silver maple, 10 Mg( OD) ha· year" ; *
Eastern Kansas alluvial sandy sites--cottonwood, 10;
Siberian elm and black locust, 6; and silver maple, 4
1
1
Mg {OD) ha" year· •
Whereas annual woodgrass (0.3 x 0.3 m) yields on alluvial
loam would be.as follows: black locust, 9; cottonwood,
siberian elm, and silver maple, 6; and honey locust, 4 Mg(
1
1
OD) ha· year· •
Lisa Sennerby-Forsse:
Field experiments with selected
willows have shown the potential of biomass production when
nutrients and water are not limiting factors.
The
production level in such trials is very high for
Scandinavian climatic conditions with maximum yields of
1
1
For practical scale plantations,
36 Mg (OD} ha" year· •
1
1
existing figures suggest 10 to 12 Mg (OD) ha" year" to be
realistic expectations, provided that rather good
cultivation sites are used, fertilization up to 100 kg N/ha
is added each year, and no irrigation during "normal
268
years. "
This is calculated on a 3 to 5 year rotation time
with 15 to 20,000 cuttings per hectare.
Louis zsuffa:
on an operational basis, willows in canada
can be expected to produce average yields of 10 to 12 Mg
1
1
(OD) ha· year· with current technology.
In plots of
1
several hundred trees, yields as high as 26 Mg (OD) ha·
1
have been measured.
Based on very small Plots ( 4 to
year·
10 trees), yields of about 40 Mg (OD) ha·1 year· , have been
measured.
With selection and properly calibrated
1
1
yields of 20 to 25 Mg (OD) ha· year· could be
nutrients,
operationally achieved within the next 5 to 10 years.
Edwin White:
current data on SRIC are essentially all from
relatively small research plots and thus indicate
1
1
potential; that is, upwards of some 40 dry Mg ha· year·
with woodgrass willows.
However, current efforts indicate
1
1
yields in the range of 8 to 12 dry Mg ha· year· are
obtainable with current cultural systems.
It is reasonable
to expect that with improved cultural techniques, for
example, clone-site match, fertilization, breeding
programs, spacings and cutting cycles, these yields can be
doubled.
Question
3: Recommended Cultural Strategy
Dean DeBell:
For poplar clones, cultural strategies
approaching conventional pulpwood systems (spacings of
1.5 m to 3.0 m and rotation ages of 4+ years) seem likely
to be the most economical for producing energy feedstock
using today's technology.
Annual yields will be as high or
higher, production costs will be lower, and the
characteristics of biomass produced will generally be more
favorable for many conversion technologies than those
occurring with more densely planted, more frequently
harvested strategies.
If biomass characteristics produced
by woodgrass strategies are especially advantageous to a
given conversion technology and the industry is willing to
pay a premium price for such traits, my opinion would
change accordingly.
Chuck strauss:
The P.lantation costs for biomass, after
1
harvest, were $35 Mg. (0D) for the nonfertilized strategy
1
and $38 Mg. (0D) for the fertilized strategy (averaged
between the two sites and for. the two rotations).
Irrigation as a separate strategy or in combination with
fertilization resulted in a tripling of production costs.
In the nonfertilized strategy, the prorated cost of
establishing the plantations amounted to 36% of the
production costs.
The remaining 64% of costs were devoted
to spray maintenance programs, managerial expenses, and
land costs.
In the fertilized strategy, cost distributions
were 28% for establishment, 49% for maintenance and
management, and 23% for fertilization.
The additional
costs of harvesting and storing biomass ranged from $30 to
1
$50 Mg. (0D), depending upon the type of harvesting system
and moisture content requirements of the feedstock.
In the
269
least-cost scenario, the total cost of supplying biomass to
an ethanol plant was $66 Mg·1 (OD).
Wayne Geyer:
The cultural system to be used on first
rotation operational SRIC plantings at about 1.3 x 2.68 m
spacing should be:
*
site preparation previous fall, apply herbicide (Roundup) and plow or disc later; *
1-m wide Devrinol strip over planted seedlings in early spring; *
two or three cultivations if herbicide strips haven't
controlled weeds well; and
*
repeat the weed control in the second growing season.
succeeding coppice rotations may need herbicide or
cultivation the first season depending upon species (i.e.,
cottonwoods and Siberian elm may need weed control but not
silver maple or black locust).
Lisa Sennerby-Forsse:
The cultural system most commonly
used in sweden is to establish willow plantations on good
agricultural soils at an initial density of 15 to 20,000
trees per hectare. The stem cuttings are allowed to grow 1
year and then are cut to produce coppice growth. The
rotation period is 3 to 5 years, with harvest age dependent
on growth response. Plantations are usually fertilized
each year at 100 kg N/ha divided between two applications
in June and August. Irrigation may be recommended for
establishment of the cuttings but is not normally used
following the establishment year. site preparation
includes cultivation and herbicide use 1 year prior to
establishment and during establishment year with intensity
depending on previous history of the site. Good site
preparation is stressed. Insecticides and pesticides are
not recommended. In operational plantations, 5 to 10
clones are established in monoclonal blocks. Actual
designs depend mainly on site characteristics.
Louis zsuffa:
For wide spacings (2 m or greater) and
rotations greater than 5 years, poplar selections are
better than willows. If growing woodgrass as a biomass
energy feedstock, then shrubby willow selections would be
better. In either case, crops should be grown on good
agricultural sites and fertilized as required by the clone
and site.
Edwin White:
Clone-site selection (good sites), adequate
site irrigation and tending, fertilization prescriptions,
and spacing and coppice rotation strategies are necessary
parts of cultural systems that will lead to increased
yields. Apparently poplars are better suited to "longer"
rotations, that is, 5 to 10 years, and willows to "shorter"
rotations less than 5 years.
Question 4: Research Needed
Dean DeBell:
The matters that concern me most with respect
to operational production of biomass feedstocks are yield,
270
G
harvest technology, and provision for year-round supply.
Impressive yields have been obtained with some poplar
clones in small experimental plots on good sites, but
little data are available to assure us that such yields can
be obtained over large acreages or that sufficient amounts
of land capable of such production are available for
bioenergy farming.
In many areas of the country, disease
problems make plantings of the high-yielding poplars a
risky venture.
More research effort is needed on other species having good
growth rates over a wide range of sites; for example,
maples, sweetgum, and alders.
The weakest link in present economic evaluations of
bioenergy feedstock production seems to be harvest
technology and harvest costs; for 20 years, engineers have
said that harvesting was the easiest problem to solve, but
we are still in a very speculative mode.
Finally, questions and problems surrounding year-round
supply must be addressed.
Biological, environmental, and
economic considerations may pose severe constraints on
harvest schedules.
Most species should not be harvested
during the growing season if coppice regeneration is
desired, and many of the most productive bottomland soils
should not be traversed by heavy equipment during major
portions of the dormant season.
Long-term storage of
harvested biomass or reliance on other energy feedstocks
during major portions of each year may be required.
Charles strauss:
Reductions in the total supply costs of
woody biomass will be primarily dependent upon securing
more efficient methods of harvesting and storing the
product.
Secondary reductions could also be secured in the
cost of inputs required by the plantation stage of
operations.
In tandem with these savings, an increased
production of biomass could be obtained by using alternate
clonal varieties of Populus and certain manipulations of
rotation periods. Overall, the intensive culture of woody
biomass represents a major investment of financial
resources within the production, harvesting, and storage
stages of the supply system.
Alteration of input or output
parameters within the system can induce substantial changes
to the final cost of the product.
Wayne Geyer:
Further effort must be made to reduce
establishment costs, increase annual yields, and shorten
cutting cycle.
These goals may be attained by:
*
direct seeding in some locations;
*
better weed control herbicides--tank mixing of
various chemicals;
*
genetically improved growth of silver maples,
cottonwood, and Siberian elm;
*
resistance to borers in black locust species; and
*
resistance to septoria and rust in hybrid poplars.
271
Lisa Sennerby-Forsse:
We have very little knowledge
regarding the sustainability of intensively managed
It will be most important to select
coppicing systems.
clones with a good and durable ability to produce new
This also implies plant
shoots after repeated harvesting.
stock with resistance not only to leaf rust and stem
cancers but also to stump or stool decay.
The
physiological and morphological factors behind the
coppicing phenomenon are not well known and need further
investigations in order to create instructions for a highly
,productive and sustainable growth system.
When we have the
indications of what characteristics are the most important
ones (we already have some knowledge in the area today) the
breeding strategy will be most important.
The stand
dynamics, including interactions and competition
aboveground and belowground, are important to know more
about when it comes to reduction of yield and composition
of mixed plantations (different trees and/or clones).
For the development of the SRIC or woodgrass concept, of
course much work is needed on economics and infrastructural
obstacles in society which today act as breaks for the
market development.
Louis Zsuffa:
Much breeding and selection work has been
done in poplars and willows but without much focusing.
We
need to develop a " model" tree for each major production
strategy and conversion pathway.
It is important to look
carefully at the genetic characteristics needed for biomass
trees according to the planned cultural strategy. There
needs to be a better focus for the genetics and physiology
work, that is, we need to know what we want to use the wood
for. Characteristics which will always be important,
regardless of the energy conversion pathway used, will be
total yields and disease resistance.
In order for
woodgrass systems to be economical, breakthroughs in
establishment systems are required. Breeding and
establishment of plantations on good sites should be
recognized as " up front" investments for biomass production
systems.
Government intervention is needed to guarantee
some kind of rent on the land.
Efforts are needed on the sustainability of
Edwin White:
the cultural systems; that is, how long and how many
rotations of " wood grass" from a single planting? Breeding
programs need to develop specific clones for both
conversion and for production in the accepted cultural
systems. Fertility prescriptions are virtually
nonexistent. Basic and applied research is needed on
nutritional and moisture requirements and the physiological
basis of coppicing.
We do not know how to handle coppice
rotations.
Practical efforts are needed on reduction of
establishment costs, harvesting technology is needed, and
markets are critical.
27 2
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SUMMARY
For the most part, the experts working with SRIC and
woodgrass systems agree more than they disagree on all of
the issues addressed. The "best" species (or clone),
spacing, and rotation age strategy depends on site
qualities, time constraints for payback or cash flow, and
the desired energy feedstock qualities. Based on current
technology, dry-weight productivity and economic viability
appear to be most favorable with SRIC rotation lengths of
SRIC stands result in a homogeneous
3 to 10 years.
feedstock suitable for most conversion technologies being
considered.
Clearly, much research remains to be done to
improve yields and protect against diseases for all
feedstock production strategies.
Considerably more
research has been done on SRIC than on woodgrass,
contributing to it's current economic advantage.
As long
as yields obtained by SRIC systems equal or exceed
woodgrass yields, it will continue to have an economic
advantage for most, if not all, energy uses.
However, in
order for SRIC biomass to be competitive with coal, gas,
and oil as an energy feedstock, further cost reductions
must be made. Development of efficient harvesting systems
will be extremely important. Woodgrass is relatively easy
to harvest but major reductions in planting costs must be
made before it is economically viable. Increasing the
efficiency of producing liquid fuels or methane must
involve matching species, clones, and cultural systems to
conversion pathways as well as to site limitations.
As was
concluded by Don Klass, each of the biomass production
strategies discussed is a valid area for research.
ACKNOWLEDGMENTS
The work of the authors, L. L. Wright, D. s. DeBell,
H. Strauss, and w. A. Geyer, has been sponsored in total
or in part by the Biofuels and Municipal Waste Technology
Division, u.s. Department of Energy, under Contract DE­
AC05-840R21400 with Martin Marietta Energy Systems, Inc.
The participation of L. Sennerby-Forsse in this panel
discussion was funded through sweden's Energy Forestry
Project at the swedish University of Agricultural Sciences,
in Uppsala, Sweden. L. Zsuffa's work on willows and
poplars at the University of Toronto is funded primarily
through several government (Canadian) and industry grants
and contracts.
Edwin White's work on willows and poplars
has been cosponsored by the New York State Energy Research
and Development Authority and by the Gas Research
Institute.
c.
273
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REFERENCES
1. Dula, J. c., " Woodgrass production for energy
application, " In:
Argonne National Laboratory, Energy
Building on a Generic Technology Base,
from Biomass:
Proceedings of the 2nd Technical Review Meeting.
Wilsonville, OR. April 23-25, 1984. p. 185 (1984).
2. Mitchell, c. P., "The European Forest Energy Scene, "
Biomass for Energy and Industry, 4th E.C.
p. 54-58, In:
Conference. Elsevier Applied Science, London, (1987).
3. Ranney, J. w., L. L. Wright, and P. A. Layton,
" Hardwood Energy Crops:
The Technology of Intensive
Culture." Journal of Forestry 85:
17-28, ( 1987).
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