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4th International
Scientific Conference
on Hardwood Processing 2013
7th- 9th October 2013
Florence, Italy
PROCEEDINGS
© CNR IVALSA
ISCHP 2013
ISBN 9788890927300
Supported by:
Conference Chair: Stefano Berti
Graphic Design: Compagnia delle Foreste S.r.l. - Arezzo, Italy
The presented papers reflect the opinion of the respective authors.
Information contained in this document has been obtained by the editors from sources believed to be reliable. Authors of specific papers
are responsible for the accuracy of the text and technical data. Neither the publisher nor the editors or authors shall be responsible for any
errors, omissions, or damages arising out of use of this information.
3
PREFACE
ISCHP 2013 is part of the continuing series of conferences previously held in Canada (2007), France
(2009) and USA (2011). The main objective of this conference is to bring together the scientific and
research communities working on hardwood, from the source to the customer, in order to share knowledge
and ideas. International experts, scientists, government employees, hardwood industry representatives,
suppliers and customers are invited to discuss recent progress and innovative work in this valuable area.
ISCHP promotes the responsible use of the world’s leading sustainable, renewable, carbon-absorbing material.
Topics covered by ISCHP 2013:
Hardwood Forestry Practices & Wood Quality
Hardwood Processing & Optimization
Hardwood Product Development
Hardwood Market & Sustainability
This year, ISCHP was organized by Cnr-Ivalsa Trees and Timber Institute, Italy. All 37 peer reviewed publications
in the proceedings were subject to a rigorous one-sided blind peer review process with a minimum of two reviewers
plus an editorial review.
EDITORS
S. Berti
A. Achim
M. Fioravanti
T. Lihra
V. Loewe Muñoz
R. Marchal
J. Wiedenbeck
R. Zanuttini
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International Scientific Conference on Hardwood Processing (ISCHP 2013)
Mona Lisa wood Pavillon: optimization and parametric design by
using poplar plywood
Guido Callegari1, Gaetano Castro2, Rian MD Iasef1, Antonio Spinelli1*, Roberto Zanuttini3
*
Corresponding author: Antonio.spinelli@polito.it
1 Department of
Architecture and Design.
Politecnico di Torino
Turin, Italy.
2 Consiglio per la ricerca e la
sperimentazione in agricoltura PLF
Casale Monferrato, Italy.
3 Department of
Agricultural, Forestry and Food
Sciences. University of Turin
Turin, Italy.
ABSTRACT
The paper illustrates the results of an interdisciplinary work flow concerning the design and construction of a
prefabricated structure using poplar plywood. The study, promoted by Politecnico and University of Torino, is
related to the development of a local wood resource focussing on the most traditional and important panel in Italy
which, from a consolidated position in the furniture market, is now searching potential and innovative applications
especially in the building sector, where the use of modern wooden materials is growing quickly. The Mona Lisa
Wood Pavillon investigates the wood design issue from three main points of view. First, the structure is part of the
promotion path of poplar plywood, conceptualizing its manufacturing process in an architectural project; then it
highlights the role of technology by using an engineered veneer-based product with interesting properties; finally
it explores the role of digital design in exploiting the potentialities of the material, in particular through a
parametric approach which permits the optimization of design and construction. The project was carried out
thanks to the joined efforts of complementary sectors and to the coordinated work of architects, engineers and
wood experts. The resulting architecture was built on the occasion of the 2012 Made Expo event, with the
patronage of the Italian woodworking associations Federlegno, Assopannelli and Conlegno, together with the
technical contribution of several industrial companies, which have sustained this research with the aim of
developing a manifesto for a better knowledge of poplar plywood.
1. INTRODUCTION
The Mona Lisa Wood Pavilion is the outcome of a research project developed by Politecnico di Torino, University
of Torino and some institution and enterprises of the Italian wood and plywood sector. Starting from the Mona Lisa
workshop, we want to foster an experimental study, referring to a number of international teaching models, that exam
the potential of computational technologies in architectural projects producing three-dimensional structures with flat
elements in plywood. The initiative is part of the more general framework of experiences, part didactic and part
research, that the Department of Architecture promoted with particular reference to the process of innovation in
construction technologies using wood.
Figure 1_ Different Pavilions realized in the field of academic research
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International Scientific Conference on Hardwood Processing (ISCHP 2013)
The Mona Lisa workshop took the name of Leonardo da Vinci’s famous painting, which was produced on a poplar
board between 1503-1514, as its icon and cultural reference, in order to highlight the theme of valorization of poplar
plywood in the area of technological and design research, this being the aim pointed out by the industrial partners in the
initiative (IBL, Panguaneta, Invernizzi, Cima, Vigolungo, Toro Compensati).
The merger in Leonardo’s work between art (ability) and science (knowledge, theory) was the cultural basis of the
research project developed during the workshop, which focused on the creation of a manifesto on the value and
potential of poplar in architecture. The enigmatic expression of Lisa Gherardini, the Gioconda – also known as Mona
Lisa – reveals how Leonardo's approach to scientific knowledge was visual, considering the eye as his main instrument
and drawing as the resource to formulate his conceptual models. Through his activity, Leonardo da Vinci made it clear
for the first time that the field of science and the field of applications were inseparable. His work reveals a concept of
design and procedure that is extremely modern, where the “inventor” is someone who creates a product or a work of art
by combining the various elements into a new configuration never to be seen in nature, through continuity between the
process of design – i.e. the abstract configuration of various elements – and their material incorporation (As made clear
by Fritjof Capra in his text “The Universal Science: art and nature in Leonardo’s genius”, Leonardo da Vinci was more
interested in the process than in the physical realization of his projects. Most of the machines and mechanical devices
he described in his drawings and technological sketches were never built. Few of his plans of military and civil
engineering ever became concrete. Even as a painter he often seemed more interested in the solution of problems of
composition than in the effective completion of the work).
For Leonardo, painting is art, but also science, a science of natural shapes based on the study and observation of
living shapes, continuously molded and altered by innate processes: rocks and sediments of the earth shaped by water,
the anatomy of animal bodies in movement, the development of plants, molded by their metabolism and botanical
diversity.
This dimension of investigation formed the basis of the work described hereafter, and turned out to be fundamental
for a structured workshop, even more than for the goal of developing an architectural project on the study and analysis
of the specific characteristics of a wood species like poplar with the features and peculiarities that determined the nature
of the Mona Lisa Wood Pavilion.
Like other similar international experiences taken as reference, the design aspect was developed starting from an
in-depth analysis of the poplar products for construction prepared by the industrial partners of the initiative, which
emphasized and focused on the development of panels combining functional and innovative features, capable of
satisfying the increasing demand for specific technical and performance characteristics.
The activity was structured in the form of a project workshop, through the coord ination between the courses of
architectural technology (prof. G. Callegari with arch. A. Spinelli, Politecnico di Torino) and construction methods
(Prof. M. Sassone, Politecnico of Torino), and involved students at the Department Architecture and Design of
Politecnico di Torino in the three levels of training (Bachelor of Science course in Architecture, Master Degree in
Urban Architecture Construction, Ph.D in Architecture and Building Design), organized in the sphere of the “Woodlab
project” serving for the cultural promotion of the initiative ( financed by funds for students project at Politecnico of
Torino, aims to create an interest and network of people and institutions around the theme of innovative use of wood in
construction).
Figure 2_ Monalia Wood Pavillion at MadeExpo (© R.Cortese, 2012).
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From the standpoint of method, after a first stage of study of poplar, preparatory to the workshop, the activities
focused on the most significant international experiences of three-dimensional architectural design in plywood.
Computational design enables architects to integrate ever more multifaceted and complex design information, while the
industrial logics of conventional building construction are eroding rapidly in a context of increasingly ubiquitous
computer-controlled manufacturing and fabrication. A novel convergence of computation and materialization is about
to emerge, bringing the virtual process of design and the physical realization of architecture much closer together, more
so than ever before. (Menges, 2012)
This permits to optimize all the potentialities of material features and design techniques, allowing the freeform
research in the field of plywood. The particular need to create a structure that would exalt the peculiarities of poplar
wood (light weight, pale color, extreme uniformity with barely perceptible veining, ease of processing, gluing and
finishing) centered the initial part of the workshop activities on the production and processing of plywood, and
characterized the end product.
Poplar has by now achieved a certain maturity in the field of plywood, in terms of development (for the high levels
of productivity attained) and market. It is therefore possible to identify certain margins for improvement with reference
to the potential for innovation determined by its diversification, through alternative uses in non-traditional sectors and
the development of products with higher added value, capable of optimizing its specific features in respect of the needs
of conformity to qualitative and performance standards, reliability and eco-compatibility (Zanuttini, 2003; Castro,
Zanuttini 2008). It is in this concrete perspective that the experience of the workshop acquires relevance through the
realization of a showpiece product – the Mona Lisa Wood Pavilion – serving to create a manifesto on poplar and
explore the uses of this wood species in architecture
2 POPLAR FEATURES
Poplar is a fast-growing tree, of many species/clones, easy to propagate vegetatively, and highly adaptable to
different climatic and soil conditions. These attitudes, combined with the wide range of wood, fiber, fuel and other
products and services provided, have led to the widespread cultivation of poplars, mostly in plantations, at present in
Europe the total amount of Poplar cultivated area is about 1 million hectares (Coaloa 2009). Considering that
plantations, which can be certified in terms of sustainable management, can significantly contribute to the reduction of
the pressure on natural forests, it is estimated that in the near future most of the timber for the wood industry will derive
from dedicated stands grown in an arboricultural system.
In Italy poplar is still the only renewable domestic source of wooden raw material which can be planned, capable of
meeting the needs of industry over the (relatively) short term, since it has a growth cycle of 10-12 years. Poplar wood
products have been confirmed as highly competitive and hard to replace both in the furnishing sector, where they are
used in various forms (mainly plywood and particle-board), and for some types of packaging for fruits and vegetables.
The CRA-PLF (Research Unit for Intensive Wood Production) deals with studies on various fast growing species
(such as willow, eucalyptus and black locust), suitable for intensive wood production for industrial uses, but its main
activity is focused on poplar (Castro and Zanuttini, 2008). Here, research work is chiefly aimed at developing new
poplar clones with particular qualities such as quick growth, disease resistance and high-quality wood that is adaptable
to varying soil environments. A few of the poplar clones obtained, after having successfully undergone experimentation
Figure 3_ Different ways of using plywood panels by computational design architecture.
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in Italy and France, have been recently protected by Community plant breeder’s rights, and, being registered in the
National Register of Forest Clones (RNCF), they are now available for commercialization in Europe.
The last part of the breeding activity, which can only be carried out on 9-10 years old plants, involves the assessment
of the wood suitability for industrial applications. This is partly done through laboratory tests (to assess technological
characteristics) and partly in cooperation with plywood industries (to evaluate the peeling attitude, as this is by far the
most important transformation for poplar wood in Italy), following the method in use at the CRA-PLF (Castro and
Miegge, 1999; Alga et al., 2008).
In fact, among several possible uses of the Italian poplar, plywood is the most important; being by far the most
remunerative, it also represents the main target for poplar growers. Poplar plywood is nearly always destined to the
furniture sector (including motor-home applications) because its low density and light colour are very appreciated and
practically impossible to achieve with alternative, more economic or easier to work materials.
However, plywood is already a “mature” product for which further developments and applications are hard to
imagine, it suffers from the ever increasing use of new and competitive wood-based products (e.g. OSB) and the
number of “technical applications” whose strict requirements are hardly met by other panels are rather limited
However it must be pointed out that the reason why the range of potential applications of poplar wood is still quite
small, lies not in its “weak” points (like low natural durability and quite poor mechanical properties) but mostly in the
fact that its use as solid wood or in wood-based panels for structural purposes is still quite limited in many Countries,
like Italy, where poplar is traditionally cultivated in specialized plantations. In many other geographical areas,
however, - Canada, United States, France, Germany and some North-European countries among others - the use of
poplar wood for structural applications is much more frequent, and solid wood (typically beams) is often substituted
with the so called “engineered” products, specially designed to meet specific performance requirements.
The main reasons of their success are the following:
•Optimization of physical-mechanical behaviour and reduction of wood variability, obtained through selection of
the raw material and a controlled re-composition, in order to obtain more isotropic and homogeneous final products;
•Improvement of the durability, reached by chemical or physical means (i.e. treatments or choice of adequate
adhesives).
Thanks to these advantages, these products - plywood included - have been able to gain important sectors of the market.
In this way a product considered a “commodity” (semi-finished product for general purposes) can be changed into a
“specialty” (i.e. a service-product aimed at satisfying a well defined/specific use) (Castro and Fragnelli, 2006).
As an example, the following diagram shows the mechanical performance of plywood made with the new clones
and with ‘I-214’; it can be easily seen that some of the new clones show significantly higher bending strength, while at
the moment none has a comparable low density (and light colour).
Figure 4_Resistance of plywood specimens made by different clones from recent selection in Italy (average values) and
comparison with ‘I-214’. The basic density refers to solid wood.
In this context, poplar wood is much appreciated for its visual aspect and for the high-quality finishing achievable.
Due to precise breeding choices and to the intensive cultivation techniques adopted, it generally shows low density and,
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International Scientific Conference on Hardwood Processing (ISCHP 2013)
accordingly, poor mechanical properties (even if compared with aspen, yellow poplar or other similar wood species
which grow in a forestry environment). However, thanks to its high performance-to-weight ratio, its structural
efficiency is very interesting and, should the market require poplar wood with improved strength properties, farmers
would be ready to plant new clones, other than the widely known ‘I-214’. These, in addition to growing faster, present
a denser and more resistant wood (20 – 30 % stronger than ‘I-214’, and even more) but at present they are not cultivated
on a large scale because their wood is less appreciated by the plywood manufacturers for the traditional use in the
furniture sector. The mechanical properties of the plywood obtained from the above clones, according to the results of
preliminary tests, proved to be significantly higher than those of analogous panels made with ‘I-214’; together with the
greater amount of raw material obtainable, this makes the new clones particularly suitable for innovative uses, in
particular in the building sector, with or without structural functions, in which the performance aspects are determining.
2. MONA LISA PAVILION WORKSHOP: A FRACTAL FOREST
Contemporary architecture of the 21st century had to face the trend towards complex forms. The recent
development of cutting-edge computational parametric design, digital fabrication and rapid prototyping systems
developed this taste in present architectural styles enormously and rapidly. ‘Mona Lisa Pavilion’ is an outcome of the
WoodLab workshop which was started with the intention to produce an architectural showpiece that can use advanced
digital-aided design and fabrication technologies and become contextual to the contemporary trend of architectural
styles. The aim of the workshop was to produce an architectural showpiece that will serve to create a manifesto on
poplar and to explore the uses of this wood in architecture.
2.1. DESIGN CONCEPT: RECREATING A POPLAR FOREST
The main objective of the workshop was to promote poplar plywood and to exhibit its versatility in an innovative
way for creative purposes in the industrial sector. The intention was to showcase the unique quality of poplar plywood,
which is smooth in color, lightweight, flexible and easy to cut. To achieve this challenging task, design ideas were
communicated through sketches. The concept development exercise started with a thread, ‘cannot an architectural
piece be a visual narration of a story of the production of construction material itself, if its intention is to emphasize the
material’s usefulness and versatility’? Poplar sprouts from its seed, and then gradually grows into a young plant and
finally a full-grown woody tree. Poplar trees altogether exist in a plantation like a family, provide shading to others and
finally they become useful for making plywood needed for manufacturing furniture, interiors and architectural objects.
The growth and age of a poplar tree is recognized by the increasing of its height, trunk radius and number of its
branches. All these elements, which mark poplar’s growth, were symbolically taken as design vocabularies to narrate
the design concept. Therefore, the idea was to recreate a poplar plantation as a human designed pavilion that can shelter
us and provide furniture for human needs. However, this whole conceptual idea had to be transformed into a design
model.
Figure
4_ Replication of poplar tree growth. Left: poplar growth annually and its representation by design elements. Right: f
ront view of
Fractal Pavillon.
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The first step of transforming the idea into a design model was done through hand sketch drawings. For this
workshop project, sketching played the foremost and most significant role, helping students to externalize their idea
into a design model. They dedicated the longest hours of this workshop to this brainstorming phase, because thinking
and simultaneously drawing sketches is a tool to solve problems, create new ideas and assist communications (Hank
and Belliston, 1992). Although sketching eases the process of transforming the idea onto a sheet at early concept level,
an additional device is necessary to take the design to a more detailed level. Recent development of digital design
makes it convenient to develop a detailed design from sketches. The first conceptual model was generated in SketchUp
for quick visualization and understanding of the design concept transformed by hand sketches (Figure 5). However,
advanced development of computer aided design using parametric modeling and computational techniques as powerful
tools take this concept externalization stage a step further for form generation and optimization based on defined
parameters and rule-based constraints.
Figure 6_Parametric modeling in Rhinoceros, (a) A ‘tree’ unit with branches, (b) Parametric modeling of pavilion
profile, (c) Parametric modeling of sitting benches, (d) Unrolled components on XY plane ready for CNC cutter.
For generating a parametric model of the pavilion, Grasshopper scripting was used in Rhinoceros. This was done in
two different parts. First part dealt with generating ‘tree’ unit with branches (Figure 6a), whereas second part for
modeling two long benches that defined the pavilion margins (Figure 6c). In the first part, branches were produced by
fractal logic of iterative process, bifurcating a trunk into two branches; each branch was then again split into two
branches and so on until the third iterative steps. The aim of the branch production process for making a ‘tree’ unit was
to follow the growth phenomena of poplar tree, thus imitating nature. However, this part was a challenging task for the
students, because the ‘tree’ units had to be designed such a way as to make it possible to realize them using real poplar
plywood, showing its versatility, but taking into consideration its strength and weakness points. Moreover, the
branching pattern needed to be parametric so that, if necessary, it was possible to achieve the desired configurations of
‘tree’ units by changing the parameters, taking into considerations the low cost, less material and simple
constructability in mind. In the second part, making benches was an easy but a tricky task. Conceptually, each piece of
bench had to represent a poplar seed and its successive growth until its final use as furniture, i.e., a complete sitting
bench. By using simple Grasshopper scripting, students could easily produce the benches in the desired, although
comfortable, sitting. Parametric tool allowed students to optimize the number, sizes and thickness of the bench pieces
easily keeping costs low and using the minimum amount of material. However, the tricky task in modeling the benches
was to merge them with the base of each ‘tree’ unit, which was a part of the whole sitting bench, with the additional
backrest. After completing the digital model of the complex shaped Mona Lisa Pavilion (Figure 6b), each design
component was unrolled on XY plane to make it ready for cutting in a CNC cutter (Figure 6d).
2.2. DIGITAL DESIGN & PARAMETRIC MODELING
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2.3. REALIZATION
As soon as the parametric modeling of the pavilion was finally completed on the computer, a small scale (1:20)
physical model was made (Figure 7a) to assess its physical behavior: every piece was cut in a CNC cutter in FabLab
Torino, and all pieces were assembled to get the final physical outcome. No serious problem appeared because of the
smaller scale, except the heavy exposure of too many metal bolts used for jointing pieces. But, in making real scale
physical prototype, we faced two main challenges. The first challenge was to create one long but complete strip by
jointing two different pieces of poplar plywood boards. This was done through ‘loose tongued joints’ (Figure 7b). Four
such strips were jointed together by screwing tightly with brass screws, so that the colors of poplar and brass screws
could merge to avoid the heavy exposure of metals (Figure 7c) However, the joints had to be made strong enough to
carry the load of the upper part of the strips, i.e., the group of branches which acted as cantilevers.
Figure 7_ (a) Small scale (1:20) physical model, (b) Loos tounged joint, (c) Connection of two ply pieces.
For physical testing of internal stresses and bending behavior, students jointed two larger curve-shaped strips in the
University workshop building and then pulled the tails of each strip manually for getting large deflection bending in
order to obtain the curved branching configuration. At certain level of stress a crack appeared at the bent area due to
torsion effect. Therefore, jointing plywood pieces was not the only critical aspect since ensuring the crack-less large
deflection of bending was the another main challenge. Accordingly, in real scale production of one ‘tree’ unit, screws
were placed diagonally at turning position but not perpendicular to the tangent of bending curve so that it would not
only ensure crack-less bending but also offer a relaxation space in torsion. One of the most important elements was the
wedges for generating branches. A triangular wooden wedge was produced on the basis of the dimensions provided by
the Rhinoceros model of a branch (Figure 6a) and then it was inserted between two strips, thus the wedge forced the
strips to deform outwards in opposite directions, forming the branch. The sides of the wedges were gently curvilinear so
as to give branches a natural shape (Figure 8).
Figure 8_ Creating branches by inserting curved triangular wedges for making physical model and protypes.
The next step of the workshop event was to start realizing all individual components for making a real scale
prototype of two ‘tree’ units. After cutting all pieces in a CNC cutter, all the components were assembled and connected
to form two different ‘tree’ unit prototypes. Two units were then placed facing each other to observe their structural
stability as well as their aesthetical appearances (Figure 9). The final and last challenge was yet to be faced: realization
and installation of the complete structure in real scale. After a long period of designing, modeling, structural testing and
making prototype units, final production of all units was done in an industrial workshop building by the industrial
participants and supervised by WoodLab team from Politecnico di Torino. Then all assembled units were transported
to the exhibition center in Milan two days before the event of ‘MadeExpo’2012’ exhibition. It took one full day to
fabricate and install the final real scale pavilion structure on the event site, and on the first day of exhibition it was
finally ready for inauguration.
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Figure 9_ Production progress of real scale ‘tree’ unit in the university workshop.
The final and successful outcome of the Mona Lisa Pavilion and the overwhelming appreciations by visitors at
exhibition centre rewarded the WoodLab team of all the work done: right from the evolution of their design concept
through conceptual sketching to parametric modeling, and from small-scale prototype testing to final real scale
fabrication and installation. In a way, it was the success of WoodLab workshop that offered students multi-dimensional
lessons and the occasion to learn some parametric and fabrication skills.
Poplar plywood could be a key leverage point in the field of sustainable wood structure, enhancing great potential in
architectural design and engineering concepts. Computational design could achieve the performance of the material
and translate in input for the project, permitting a close relation between functionality and sustainability.
ACKNOWLEDGEMENTS
The Mona Lisa project has been possible thanks to the contributions of many individuals, institutions and private
organizations such as the Politecnico di Torino, Conlegno, Federlegno, Assopanelli, Pro-Populus, FabLab Torino, the
C.R.A.-PLF Institute in Casale Monferrato and the University of Turin. An important role in the fate of the project was
played by the companies who have supported the initiative, not only through sponsoring, but also with technical support
for the works, identifying certain key aspects. For a complete list of companies see the official website of the project
(www.woodlab.polito.it).
REFERENCES
Aichim Menges (2013) Material Computation Higher Integration in Morphogenetic Design, March-April 2013
Alga R., Castro G., Zanuttini R. (2008). Otto nuovi cloni sperimentali di pioppo: prime valutazioni sulle caratteristiche
tecnologiche. Sherwood, Foreste e Alberi Oggi n° 41, marzo 2008: 5-10.
Callegari G., Sassone M., Spinelli A. (2013). Wood digital works, Milano, Edizioni Ambiente.
Callegari G., Sassone M.,Spinelli A., Zanuttini R., Mona Lisa Wood Pavilion: poplar pl(a)ywood, (2013) ICSA2103
(International Conference on Structures and Architecture) Proceedings, Portugal, 24-26 luglio, 2013
Castro G. Zanuttini R. 2008 Poplar cultivation in Italy: history, state of the art, perspectives, in 23rd se ssion of the
International Poplar Commission – Beijing
Coaloa D. (2009) La pioppicoltura in Italia e nel mondo, stato attuale e prospettive future. In Dendronatura 30: (1)
21-26
Gasparini P. Tabacchi G. (2011). L’Inventario Nazionale delle Foreste e dei serbatoi forestali di Carbonio INFC 2005.
Secondo inventario forestale nazionale italiano. Metodi e risultati. Ministero delle Politiche Agricole, Alimentari e
Forestali; Corpo Forestale dello Stato. Consiglio per la Ricerca e la Sperimentazione in Agricoltura, Unità di ricerca
per il Monitoraggio e la Pianificazione Forestale. Edagricole-Il Sole 24 ore, Bologna. 653 pp.
Castro G., Miegge D. (1999). Caratteristiche fisiche e idoneità alla sfogliatura di alcuni cloni di pioppo. Sherwood,
Foreste e Alberi Oggi n° 5 (4): 41-44.
Castro G., Fragnelli G. (2006). New technologies and alternative uses for poplar wood. Boletin del CIDEU n. 2: 27-36.
Castro G., Zanuttini R. (2008). Poplar cultivation in Italy: history, state of the art, perspectives. Cost Action E44
“Wood Processing Strategy”. Final Conference – Milan, ITALY May 30th - June 3rd 2008: 141-154.
Zanuttini, R. 2003 I moderni pannelli a base di legno. I.F.M.. LVIII(1), 34-53
Hanks & Belliston. (1992). DRAWΜA visual approach to thinking, Learning and Communicating
