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RISK ASSESSMENT OF LIVING MODIFIED TREES
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This guidance complements the Roadmap for Risk Assessment of LMOs giving emphasis to issues
that are of particular relevance to the risk assessment of LM trees. As such, risk assessments of this
type of LM plants also follow the general principles outlined in the Roadmap, but take into account the
specific characteristics of perennial long-living trees.
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BACKGROUND
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Forest biodiversity is a core area of work in the Convention on Biological Diversity (CBD). During its
eighth and ninth meetings, the Conference of the Parties to the CBD recognized “the uncertainties
related to the potential environmental and socio-economic impacts, including long-term and
transboundary impacts, of genetically modified trees on global forest biological diversity”,
recommended “Parties to take a precautionary approach when addressing the issue of genetically
modified trees” and urged Parties to undertake a number of actions with regard to LM trees, such as
“to develop risk-assessment criteria specifically for genetically modified trees”. 1
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Given the above decisions and the mandate by the COP-MOP to develop “further guidance on new
specific topics of risk assessment, selected on the basis of the priorities and needs by the Parties and
taking into account the topics identified in the previous intersessional period”, and on the basis of the
priority-setting exercise conducted in the Open-ended Online Expert Forum on Risk Assessment and
Risk Management, the AHTEG agreed to develop additional guidance for the environmental risk
assessment of LM trees.
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INTRODUCTION
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Trees and forests, and their vast diversity in distribution, organismic networks, species and genotypes
have significant ecological, economic, environmental, climatic and socio-economic values: forests and
fruit trees/orchards provide important food supplies (for humans and animals); wood is an important
raw material for building and construction, the pulp and paper industry, and energy production (incl.
fire wood); sequestration of atmospheric carbon is an important function in mitigating climate change;
air filtration, water and soil conservation as well as their role in local climate (micro climate), cloud
formation and rain fall patterns (due to tree/forest transpiration) are important ecosystem functions and
services. In addition forests are of high value for recreation and tourism and have cultural and spiritual
significance.
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Thirty one percent of the total global land area or more than 4 billion ha are covered by forests. 1,2
billion of these are used for production of wood and non wood products. An additional 949 million ha
are dedicated to multiple uses including soil and water conservation. Managed forests including
commercial plantations are increasing and now comprise around 7% of the total forested area (FAO
2010). Accordingly, forest trees, especially those suited for plantations, are the focus of advanced
breeding strategies including genetic engineering through modern biotechnology.
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Fruit and forest tree species of economic interest grow in various regions of the world from temperate
to tropical climates. Usually tropical forests show higher species richness combined with a higher
biomass production (per year). According to the ecological theory that high production of biomass is
combined with nutrient poor soils, tropical forests are much more sensitive to disturbances and biotic
or abiotic stresses (Begon et al. 2006).
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See COP decisions VIII/19 paragraphs 2 and 3 (http://www.cbd.int/decision/cop/?id=11033) and IX/5 paragraphs 1(s)-(z)
(http://www.cbd.int/decision/cop/?id=11648) “Recognizing the uncertainties related to the potential environmental and socioeconomic impacts, including long-term and transboundary impacts, of genetically modified trees on global forest biological
diversity, as well as on the livelihoods of indigenous and local communities, and given the absence of reliable data and of
capacity in some countries to undertake risk assessments and to evaluate those potential impacts, [...] Recommends Parties to
take a precautionary approach when addressing the issue of genetically modified trees;”
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The definition of a tree
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According to the Food and Agriculture Organisation of the United Nations (FAO), a tree is: “a woody
perennial with a single main stem, or, in the case of coppice, with several stems, having a more or less
definite crown”. Further according to the FAO, bamboos, palms and other woody plants are included
into the definition of a tree if they meet the definition above.2 Tree species belong to many different
taxonomic orders and families of angiosperms (flowering plants; e.g. mahogany, poplar, apple) and
gymnosperms (“naked seed” plants; e.g. pine, spruce, cedar).
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Characteristics of trees
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Trees can be distinguished from annual crop plants by a series of characteristics, such as a long
lifespan and unique reproductive features. Some forest tree species can live for several hundred years
(e.g lime and oak trees) up to several thousands of years (Matyssek et al. 2010). Together with a long
life cycle and late onset of reproductive organs, the vegetative phase of a tree, where only vegatative
propagation is possible, may extend from one to several decades. High fecundity (reproduction
capacity) together with seed dormancy, multiple and very effective pathways for dispersal of
propagules, extended possibilities of vegetative reproduction and high seed viability are important
aspects for the high adaptive capacity, establishment in unmanaged ecosystems and worldwide
distribution of many species of trees.
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Forest trees are valued both for their large biomass production for industrial purposes as well as for
their contribution to ecological services and landscape architecture. Root systems are extensive and are
inextricably enmeshed with mycorrhiza, symbiotic associations with fungi. In addition (forest) trees
are involved in broad interactions with further organisms from decomposers to birds and wildlife.
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Breeding and cultivation of forest trees is a quite novel endeavour in recent history (Campbell et al.
2003). In Europe, forest tree propagation and management commenced in the Middle Ages, but only
since the 19th century, have forest trees been systematically adapted to the needs of wood production
(Mathews & Campbell 2000). For this reason, even in commonly grown species, the level of
domestication is still low. Fruit trees are generally considered more highly domesticated.
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Overview of the current status of genetic modification of trees through modern biotechnology
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Currently about 30 to 40 different tree species have been modified through modern biotechnology,
mainly through the insertion of transgenes, and have been introduced into the environment for field
trials (FAO 2004, Verwer et al. 2010). The majority of these LM trees are commonly planted,
commercial species, which were modified in an attempt to improve traits related to herbicide
tolerance, wood composition (e.g. lignin), growth rates and phenology (including flowering and
fruiting), resistance to pests and diseases, or abiotic stress tolerance. By far, poplars make up most of
the LM trees that were, to date, developed and subjected to field trials, (Canada Norway Workshop
2007), followed by eucalyptus and pine. LM apples and papaya make up most of the fruit trees
approved for field trials (Gessler&Patocchi, 2007; Hanke & Flachowski 2010). Poplars are the only
transgenic forest trees planted on a commercial scale (in China, Ewald et al. 2006). Two different
types of fruit trees, papaya and plum, have been approved for commercialization (in the United
States3).
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http://www.fao.forestry/site/24690/en
See http://www.isb.vt.edu/search-petition-data.aspx.
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The OECD Working Group on Harmonization of Regulatory Oversight has published consensus
documents on the biology of most tree species of economic interest that have been modified through
modern biotechnology.4
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SCOPE OF THIS GUIDANCE
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This guidance focuses on perennial woody plants as defined by FAO (2005). In addition to forest,
plantation and fruit trees, this guidance will thus include bamboos, palms and other woody plants if
they meet the definition of a tree (see above).
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OVERARCHING ISSUES IN THE RISK ASSESSMENT PROCESS (see “Overarching issues in
the risk assessment process” in the Roadmap)
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Transboundary movements of LM trees and the Cartagena Protocol
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According to the Protocol, risks associated with LMOs or products thereof5 should be considered in
the context of the risks posed by the non-modified recipients or parental organisms in the likely
potential receiving environment. Therefore, in the case of LM trees, when characterizing the likely
potential receiving environment, risk assessors should take into account not only the movement of
seeds for intentional introduction into the environment, but also of vegetative propagules since, for
many tree species that is the preferred way of propagating them. Issues related to unintentional
transboundary movements (article 17) should also be taken into account in cases where LM trees can
cross national boundaries through, for example, pollen or seed dispersal by physical and biological
vectors, including the international trade of fruits with seeds.
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PLANNING PHASE OF A RISK ASSESSMENT OF TRANSGENIC TREES
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The Comparative approach - aspects of implementation (see “Planning Phase of the Risk
Assessment”, “The choice of comparators” in the Roadmap)
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Rationale
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As for risk assessments of any other type of LMO, a comprehensive planning phase is needed in order
to define, among other things, whether and how a comparative approach can be carried out in the risk
assessment of an LM tree.
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Trees, as long-living species with unique adaptive and reproductive characteristics and low degrees of
domestication, may present a special challenge for an assessment based on a comparative approach
developed for annual crops with high degree of domestication. The characteristics of the receiving
environment, including interactions with other organisms as well as biotic and abiotic conditions, are
likely change throughout the lifespan of a tree. As such, possibly changing adaptive capabilities over
the lifetime of the tree regarding abiotic and biotic impacts and stresses should be taken into account
where appropriate.
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In sustainable forestry the use of regional provenances is regarded as being of special importance
because of higher plant vigour, better adaptive capabilities and consequently better performances
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Up to now for 13 tree species consensus documents on their biology have been developed to support an
environmental risk assessment. These documents can be found at
http://www.oecd.org/document/15/0,3746,en_2649_34385_37336335_1_1_1_1,00.html
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“Namely, processed materials that are of living modified organism origin, containing detectable novel
combinations of replicable genetic material obtained through the use of modern biotechnology”.
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(Hubert & Cundall 2006). 6 These regional provenances and their management may display important
conventional comparators congruent with national protection goals and good forest management
practises.
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The long lifespan of trees and the higher potential for dispersal and establishment beyond the intended
receiving environment (e.g. into natural ecosystems), should be taken into account when considering
any limitations in the predictive power of a comparative environmental risk assessment.
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Points to consider
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(a)
(b)
(c)
Availability of data from glasshouse experimentation that could be used as a basis for a
comparative assessment;
Availability of regional provenances or ecotypes inside their natural range that could be
used as non-modified comparators in the likely potential receiving environment;
Design of field trials and whether these would be conducted for a period that is long
enough to reveal the differences in the LM trees as compared to the non-modified trees
(e.g. after exposure to multiple biotic and abiotic stresses,.
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CONDUCTING THE RISK ASSESSMENT
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Transformation and propagation methods (see “Step 1”, “Point to consider (b)” in the Roadmap)
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Rationale
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Back-crossing of LMOs to non-modified organisms has been suggested as a way to reduce the
presence of mutations resulting from the transformation methods and ensure stability of the modified
genetic elements. While back-crossing is routinely done for annual LM crops, it is not a viable option
for many species of LM trees which have a long vegetative period. Multiplication of trees is mostly
done through clonal and vegetative propagation, which allow for the perpetuation of modificationinduced mutations and instable genetic elements.
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Points to consider
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(a)
(b)
(c)
(d)
Propagation method(s) used;
Transformation methods;
Characterization of modification-induced mutations that could have a potential adverse
affect;
Degree or number of back-crossing, if possible, within that species.
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Long life cycles and genetic and phenotypic characterisation and stability (see “Step 1”, “Point to
consider (d) and (e)” in the Roadmap)
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Rationale
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Trees adapt to the many different abiotic and biotic conditions they encounter during their often long
lives. The phenotypic plasticity of a tree can be evidenced by changes at the transcriptome level in
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For example the Ministerial Conference on the Protection of Forests in Europe recommended “Native species and local
provenances should be preferred where appropriate. The use of species, provenances, varieties or ecotypes outside their
natural range should be discouraged where their introduction would endanger important/valuable indigenous ecosystems,
flora and fauna……”6 .
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response to various common stresses encountered by the tree throughout its life. The phenotypic
changes also involve epigenetic changes[to be added to “Use of terms”], which are especially
important for trees spread through propagules or grafting. Thus, the phenotypic characterization of an
LM tree, done in step 1 of the risk assessment, is likely to yield different results depending on the
developmental stage and environmental conditions at the time of the characterization.
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In addition transgene instability including those causing gene silencing and variable expression levels
during the long lifespan of trees should be considered (Ahuja 2009; Harfouche etal. 2011). There is
evidence that gene/environment interactions play an important role for expression level of the
transgenes (Strauss et al. 2004). Consequently, stability of transgenes and expression levels are an
important consideration, in particular where transgenic approaches are used for containment strategies
(e.g. male sterility or ablation of floral organs).
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Points to consider
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(a)
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(d)
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Genetic rearrangements or other changes over time;
Interaction with genes of the host genome and gene/environment interactions in space and
time;
Variability of expression levels, including gene silencing over time;
Influence on and stability of phenotypic characteristics over time;
Altered responses to biotic and abiotic stresses that may have a potential adverse effect on
the receiving environment;
Changed interaction with other organisms, and changed ability to maintain role and
function in ecosystems, consistent with a Party’s defined protection goals.
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Dispersal mechanisms (see “Step 1”, “Step 2”, “Point to consider (e) and (f)” in the Roadmap)
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Rationale
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Different tree species have developed a variety of ways to reproduce and disseminate via seeds, pollen
and/or vegetative propagules. Trees often produce large amounts of pollen and seed per individual and
propagules are often designed to spread far and wide (e.g. by wind, water, or animals including
insects) (e.g. Williams 2010). In addition, a number of trees have developed very sophisticated seed
“travelling” units and seeds that are capable of remaining dormant for a very long period of time
(Roloff 2004). In addition the potential for vegetative propagation is a characteristic of certain forest
and fruit trees under consideration opening the possibility of branches or root parts with living tissue
to establish new plant individuals. Seeds inside fruits may travel as commodities around the globe and
be released at the place of consumption such as road margins, railways or touristic areas, as well as in
farmers’ fields and local gardens7.
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Points to consider regarding dispersal of pollen
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(a)
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Pollen viability and pollination specifics;
Possible spatial pollen distribution, e.g. animal and physical vectors;
Timing of pollen production vs. receptivity of female flowers
Mechanism developed in some species to ensure selfing.
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The OECD Working Group on Harmonization of Regulatory Oversight has published consensus documents on
the biology of 13 species of trees to support an environmental risk assessment. These documents can be found at
http://www.oecd.org/document/15/0,3746,en_2649_34385_37336335_1_1_1_1,00.html
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Points to consider regarding dispersal of seed
(e)
(f)
(g)
Seed dormancy and viability;
Abiotic distribution (wind, water, floods etc.);
Biotic distribution via animals including humans e.g., seed dispersal via commodity fruits,
long range migratory birds, combinations of vectors such as birds and shipping;
Points to consider regarding dispersal of vegetative propagules
(h)
(i)
Presence of water ways at the receiving environment;
Possibility for dispersal of branches by animals (e.g. nesting birds) or antropogenic
activities (e.g. fire wood).
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The likely potential receiving environment(s) (see “Step 1”, “Points to consider (f) and (g)”,” Step
2”,”Points to consider (b), (d) (f) and (g) and )”,” Step 3”,”Points to consider (a) and (e) in the
Roadmap)
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Rationale
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As seen in the previous point, the identification and characterisation of likely potential receiving
environment(s) will be highly dependent on the species in question and its mechanisms for dispersal.
Given that the domestication level of trees is often low and trees can often survive without human
intervention, the dispersal of propagative material (e.g. seeds, branches) may lead to persistence and
spread of the LM tree in question. Therefore, the potential for dispersal of propagative material into
environments other than the intended receiving environment is an important consideration during the
risk assessment.
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Points to consider
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(a)
(b)
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(d)
(e)
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(g)
Nearby landscapes e.g., forests which offer the potential for seeds and/or vegetative
propagules to establish
Degree of management of these forests;
Presence and proximity of species including in orchards and gardens in the receiving
environment with which the LM tree may hybridize;
Occurrence of protected areas nearby;
Impacts on water tables and water sheds in or linked to the potential receiving
environment;
Changes in landscape patterns (e.g. because of new plantations);
Ecosystem function and services of potential receiving environment.
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Exposure of the ecosystem to LM trees (see “Step 2”, “Points to consider (e)to (h)” n the
Roadmap)
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Rationale
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Trees engage in complex ecological interactions, such as providing habitat for a number of organisms
and functioning as part of complex and elaborate food webs. In determining the likelihood of an
adverse effect to occur, an assessment of the exposure of the ecosystem to the LM tree is done over
time in the likely potential receiving environment(s), taking also into account the intended use (e.g.
processing, trade routes) as well as dispersal mechanisms (see above). For instance, a number of tree
species under exploration as transgenic bioenergy plantation trees are assessed to have the potential of
becoming invasive (Gordon et al. 2011) which could cause the time and surface of exposure to expand
indefinitely.
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Points to consider
(a)
(b)
(c)
Persistence in the environment (e.g. life span, seed dormancy);
Potential of the LM tree to become invasive;
Interactions/food webs with:
(i)
symbiotic microorganisms/mycorrhiza;
(ii) soil organisms including decomposers and pest organism;
(iii) pest organisms (e.g. viruses, bacteria, fungi);
(iv) above ground invertebrates (including predators and pests);
(v) birds;
(vi) wildlife;
(vii) humans (e.g. allergies via pollen or sawdust inhalation).
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Risk management strategies (see “Step 4”, “Point to consider (d)” and “Step 5” in the Roadmap)
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Rationale
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Risk management strategies designed for LM trees will vary significantly depending on whether the
LM tree under consideration is a forest/plantation tree or as a fruit tree. On the one hand, risk
management for forest or plantation trees may rely on strategies for delaying or avoiding flowering
(e.g. fast-growing trees for lumber production being cut before reaching the reproductive phase) and
bioconfinement (e.g. induction of male sterility or flower ablation). On the other hand, the risk
management of LM fruit trees will have to rely on different strategies since early flowering is crucial
for the fruit industry and constantly the target of different practices for tree propagation and
improvement (e.g. grafting).
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Points to consider
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(a)
(b)
(c)
(d)
Type and intended use of the LM tree;
Degree and type of management (e.g. grafting of fruit trees, rotation period of lumber
trees);
Results from monitoring of field trials;
Specific effects and risks of any bioconfinement strategy achieved through the use of
modern biotechnology.
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LITERATURE
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Ahuja,M.R. (2009) Transgene stability and dispersal in forest trees. Trees Vol. 23 pp. 1125-1135
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261
Begon, M. Townsend, C.R. and Harper, J.L. 2006. Ecology – From Individuals to Ecosystems, Fourth
Edition. Blackwell Publishing
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263
Campbell, M.M. Brunner, A.M. Jones, H.M. and Strauss, S.H. (2003) Forestry´s fertile crescent: the
application of biotechnology to forest trees. Plant Biotechnology Journal 1: 141-154
264
265
Ewald,D. Hu,J. Yang,M. (2006) Transgenic forest trees in China. In; Fladung,M. Ewald,D. (Eds) Tree
transgenesis: recent developments, Springer Berlin. pp 25-45
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267
FAO 2004. Preliminary review of biotechnology in forestry including gengetic modification.
Resources Working Paper FGR 59E Forest Resources Division
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270
FAO 2005. Global forest resource assessment. Global Forest Resources Assessment update Terms
and definitions. FRA Working Paper 83/E, FAO Forestry Department Rome 2004
(http://www.fao.org/forestry/site/24690/en)
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FAO 2010 Global Forest Resources Assessment 2010, main report 163
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273
Frankenhuyzen, K. Beardmore, T. (2004) Current status and environmental impact of transgenic forest
trees. Can. J. For. Res. 34: 1163–1180
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275
Gessler,C. Patocchi,a. (2007) Recombinant DNA Technology in Apple. Adv Biochem
Engin/Biotechnol. DOI 10.1007/10_2007_053
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277
Gordon, D.R. et al (2011) Assessing the invasive potential of biofuel species proposed for Florida and
the United States using the Australian weed risk assessment. Biomass and Bioenergy 35, 74-79
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Hanke, V. Flachowsky, H. (2010) Fruit Crops. in: Kempken, F. and Jung, C. (Eds) Genetic
modification of plants. Biotechnology in agriculture and forestry 64, Springer-Verlag . Heidelberg,
Germany
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Harfouche,A. Meilan R. Altman A. (2011) Tree genetic Engineering andapplications to sustainable
forestry and biomass production. Trends in Biotechnology, Vol. 29, No. 1
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Heinemann, J.A. 2007. A typology of the effects of (trans)gene flow on the conservation and
sustainable use of genetic resources. UN FAO Background Study Paper 35
(ftp://ftp.fao.org/ag/cgrfa/bsp/bsp35r1e.pdf).
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Hubert, J. Cundall E. (2006) Choosing provenances of broadleafed trees. Information note. Forestry
Commission UK. http://www.forestry.gov.uk/pdf/fcin082.pdf/$FILE/fcin082.pdf
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Mathews, J.H. et Campbell,M.M. (2000) The advantages and disadvantages of the application of
genetic engineering to forest trees: a discussion. Forestry Vol. 73 No. 4: 371-380
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Matyssek, R.; Fromm, J.; Rennenberg, H.; Roloff, A. (2010): Biologie der Bäume - Von der Zelle zur
globalen Ebene. Ulmer Verlag, Stuttgart. 349 S.
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OECD, Safety Assessments of Transgenic Organisms. OECD Consensus Documents. Vol. 3, 2010 :
Biology of Trees: White Pine, Jack Pine, North American Larches, Douglas-Fir, Lodgepole Pine,
Black Spruce; Vol. 2, 2006 Biology of Tress: Norway Spruce, White Spruce, Sitka Spruce, Eastern
White Pine, Poplars, Stone Fruits, European White Birch.
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A.L. Campbel M.M. (2011) Clone history shapes Populus drought responses. PNAS 108 (30) : 1251212526
Rani V, Raina S.N. (2000) Genetic fidelity of organized meristem-derived micropropagated plants: a
critical reappraisal. In Vitro Cell Biol Plant 36:319–330
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Roloff A. (2004) Trees. Phenomena of Adaptation and Optimization. Ecomed Verlagsgesellschaft
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Strauss, S.H. Brunner, A.M. Busov, V.B. Ma,C. Meilan, R. (2004) Ten lessons from 15 years of
transgenic Populus research. Forestry 77 (5) 455-465
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Verwer,C.C. Buitenveld,J. Koelwijn,H.P. Tolkamp,W. de Vries, S.M.G. van der Meer,P.J. . (2010)
Genetically modified trees – Status, trends and potential environmental risks. Alterra-report 2039
(http://edepot.wur.nl/146722)
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Williams CG (2010). Long-distance pine pollen still germinates after meso-scale dispersal. Am J Bot.
97(5):846-55.
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