The voluntary Code of conduct on invasive alien plants in Belgium: results and lessons learned from the AlterIAS LIFE+ project

The voluntary Code of conduct on invasive alien plants in Belgium: results and lessons learned from the AlterIAS LIFE+ project
Bulletin OEPP/EPPO Bulletin (2014) 44 (2), 1–11                                                  ISSN 0250-8052. DOI: 10.1111/epp.12111

The voluntary Code of conduct on invasive alien plants in Belgium:
results and lessons learned from the AlterIAS LIFE+ project
M. Halford1, L. Heemers2, D. van Wesemael2, C. Mathys3, S. Wallens4, E. Branquart5,
S. Vanderhoeven6, A. Monty1 and G. Mahy1
  Biodiversity and Landscape Unit, University of Liege Gembloux Agro-Bio Tech, Passage des Deport
                                                                                                   es, 2, B-5030, Gembloux, Belgium;
  Proefcentrum voor Sierteelt, Schaessestraat, 18, B-9070, Destelbergen, Belgium
  Centre Technique Horticole, Chemin de la Sib erie, 4, B-5030, Gembloux, Belgium
  Federal Public Service, Health, Food Chain Safety and Environment, Place Victor Horta, 40, B-1060, Brussels, Belgium
  Service Public de Wallonie, Departement d’Etude du Milieu Naturel et Agricole, Avenue Mar
                                                                                            echal Juin, 23, B-5030, Gembloux, Belgium
  Belgian Biodiversity Platform, Avenue Louise 231, B-1050, Brussels, Belgium

                                     Voluntary approaches have been recently used in the horticultural sector to deal with the
                                     introduction and spread of invasive alien plants. In Belgium, the first Code of conduct has
                                     been developed within the frame of the AlterIAS project, a LIFE+ “Information & Commu-
                                     nication” project aiming at raising the awareness of horticulture professionals and gardeners
                                     on the invasive plants issue. The Belgian Code was prepared in consultation with represen-
                                     tatives from the ornamental sector, public authorities and the scientific community. The
                                     Code was promoted throughout the country with a specific communication campaign enti-
                                     tled “Plant different”. Thanks to communication efforts, a positive dynamic of involvement
                                     was observed over time. Surveys were performed to assess the changes of attitudes and the
                                     perception of the Code by the target audience of the project. Positive results were achieved
                                     for horticulture professionals. However, the Code will require more time to be widely
                                     adopted by the ornamental sector in Belgium.

                                                                      was developed within the framework of this project. The
                                                                      budget needed for the preparation, the implementation (i.e.
Recognizing the increasingly serious problem of invasive              the promotion) and the monitoring of the Code of conduct
alien species (IAS) in Europe, the LIFE program from the              was about 450 000 EUR.
European Commission has financed numerous IAS-related                    The introduction and spread of IAP is considered as one
projects. From 1992 to 2006, LIFE financed 187 IAS-                   of the major ecological challenges of the 21st century
related projects with a total budget exceeding 44 million             (Yi et al., 2006). Ornamental horticulture is widely
EUR (Scalera, 2010). Most of them were LIFE Nature and                acknowledged as one of the main introduction pathway of
LIFE Environment projects. ALTERnatives to Invasive                   invasive plants (Reichard et al., White, 2001; Burt et al.,
Alien Species (AlterIAS) was a LIFE+ “Information &                   2007; Dehnen-Schmutz et al., 2007). Deliberate introduc-
Communication” project entirely focused on awareness-rais-            tions of invasive species through cultivation, gardening and
ing on invasive plants and prevention in the horticultural            landscape planting are starting points of plant invasions in
sector of Belgium ( The project was                  natural habitats (examples are shown in Figs 1 and 2). In
launched in 2010 with a total budget of 1 010 804 EUR for             Belgium, many invasive plants initially introduced as
a duration of 4 years. AlterIAS had three specific objec-             ornamentals are still available on the horticultural market
tives: (1) make horticulture professionals, gardeners and             (Halford et al., 2011a,b; Vanderhoeven et al., 2011). Often
students in horticulture aware about the risks of invasive            no information is delivered outside the scientific audience
alien plants; (2) collaborate with actors in the ornamental           and recent surveys showed that horticulture professionals
sector to identify alternatives and good practices in preven-         and gardeners (i.e. the general public) remain poorly
tion and (3) guide these actors to implement those measures           informed about the risks of IAP (Halford et al., 2011a,b;
through a self-regulation approach (i.e. a voluntary Code of          Vanderhoeven et al., 2011). The lack of information and the
conduct). To achieve these goals, numerous communication              continued commercial availability of IAP highlighted the
actions and tools were developed. The first voluntary Code            necessity to use preventive tools to reduce their introduction
of conduct (CoC) on invasive alien plants (IAP) in Belgium            and spread. Education, information and awareness-raising

ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11                                                        1
The voluntary Code of conduct on invasive alien plants in Belgium: results and lessons learned from the AlterIAS LIFE+ project
2    M. Halford et al.

A                                          B

                                                                                          Fig. 1 The giant goldenrod (Solidago
                                                                                          gigantea) is an invasive plant introduced from
                                                                                          North America. The plant is frequently
                                                                                          planted in gardens (A). S. gigantea may
                                                                                          escape out of gardens and become invasive in
                                                                                          riverbanks, grasslands and disturbed areas (B).
                                                                                          Photos: M. Halford (A), S. Vanderhoeven (B).

A                                          B

                                                                                          Fig. 2 The parrotfeather (Myriophyllum
                                                                                          aquaticum; syn. M. brasiliensis) is a well-
                                                                                          known invader in water ponds (B). The plant
                                                                                          is frequently sold in garden centers and
                                                                                          nurseries specialized in aquatic plants (A).
                                                                                          Photos: M. Halford (A), E. Delbart (B).

campaigns are recommended to influence future consumer            impact of these voluntary instruments may substantially dif-
behaviour and facilitating choices to reduce IAS risks (Shine     fer: some instruments may have signatories; other Codes
et al., 2010).                                                    propose general guidelines or species-specific recommenda-
   Prevention is recognized as much more effective than           tions, which in turn may be negotiated with the horticul-
control actions on IAS because of a higher cost/benefit ratio     tural sector. Finally, Codes are implemented with or
from both an ecological and economical perspective                without a communication campaign depending on the
(Vanderhoeven et al., 2011). Preventive actions may               human and financial resources available within the program.
include regulation or voluntary instruments (i.e. self-regula-    Therefore, the potential success of all these forms of Codes
tion). Voluntary approaches have been recently used in the        is highly variable. On top of this, the effectiveness and effi-
horticultural sector to deal with the introduction and spread     ciency of most self-regulation tools on IAP are poorly doc-
of IAP. Such approaches can fulfill multiple roles: aware-        umented due to the lack of monitoring implemented once
ness-raising, stimulating stakeholder involvement, dissemi-       these instruments are applied.
nation of best practices, supplementing existing regulations         This paper reports the feedback from the AlterIAS pro-
or filling a regulatory gap (Shine et al., 2010). Voluntary       ject for developing a voluntary Code of conduct on inva-
approaches are recommended in the European strategy on            sive alien plants in consultation with the horticultural
IAS which encourages the implementation of self-regulation        sector. The main results are presented, with a focus on
tools in addition to regulatory instruments.                      the methodology used, the reactions from the sector
   Several Codes of conduct or Codes of practice on inva-         and the changes of attitudes observed after 4 years of
sive alien plants are implemented throughout the world.           communication.
The first voluntary approaches being the Garden Plants
Under the Spotlights Strategy (GPUTS) developed in Aus-
                                                                  The initial situation
tralia in 1999 (Roush et al., 1999; quoted by Moss &
Walmsley, 2005) and the St. Louis Code of conduct for             In Belgium, invasive alien species are classified in the
nursery professionals implemented in the United States in         Harmonia information system, which has been developed at
2002 (Reichard, 2004). In Europe, the Code of conduct on          the initiative of scientists gathered within the Belgian
horticulture and invasive alien plants has been published in      Forum on Invasive Species ( To
2008 by the European and Mediterranean Plant Protection           help policy makers and land managers in the identification
Organization (EPPO) and the Council of Europe (Heywood            of species of most concern for preventive or mitigation
& Brunel, 2011). Following this publication, a survey con-        actions. The Belgian CoC prepared within the framework
ducted in 2011 by EPPO reported 12 national initiatives on        of the AlterIAS project was based on the list of invasive
CoC on invasive alien plants (EPPO Reporting Service No           plants available in the Harmonia information system. This
6, 2011). Despite a common goal, the content, scope and           list system of non-native organisms is built using a

                                                    ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
The voluntary Code of conduct on invasive alien plants in Belgium: results and lessons learned from the AlterIAS LIFE+ project
The Belgian Code of conduct on invasive plants                3

standardized assessment protocol, ISEIA (Invasive Species                               and shrubs such as Acer negundo, Amelanchier lamarckii,
Environmental Impact Assessment), which allows assess-                                  Cornus sericea, Buddleja davidii, Quercus rubra and
ment and categorization of exotic species from any taxo-                                Robinia pseudoacacia were the most frequent IAP found in
nomic group according to their invasion stage in Belgium                                catalogues, which suggest that they are widely used for gar-
and to their impact on native species and ecosystem func-                               dening and landscape planting. Even widespread and well
tions (Branquart et al., 2010). The Belgian list system is                              known invaders such as the Asian knotweeds (Fallopia
based on three different list categories as recommended in                              spp.), the black cherry (Prunus serotina) and the giant hog-
the European strategy on Invasive Alien Species in 2003.                                weed (Heracleum mantegazzianum) were still present in
Those categories are defined according to the severity of                               horticultural catalogues. Nursery professionals identified 32
impacts on the environment: no negative impact (white                                   invasive alien plants used as ornamentals which were con-
list), negative impact suspected (watch or grey list) and                               sidered of economic value. The top five invasive alien
negative impact confirmed (black list).                                                 plants of economic value were Prunus laurocerasus, Bud-
   Before drafting the Code, a preliminary survey was per-                              dleja davidii, Amelanchier lamarckii, Robinia pseudoacacia
formed in 2010 in order to (1) quantify the presence and eco-                           and Rhododendron ponticum.
nomic value of invasive alien plants in the horticultural                                  On average, most (75%) horticulture professionals and
market and (2) assess the perception of the invasive alien                              gardeners had a correct level of knowledge of the concept
plants issue by horticulture professionals and gardeners (i.e.                          of IAP (i.e. question related to the definition of IAP). How-
level of knowledge of the issue, degree of awareness and con-                           ever only 31% of respondents felt well enough informed on
cern, need for information, etc.). The presence of IAP in the                           the issue and 84% considered they should be better
market was completed by an analysis of horticultural cata-                              informed about IAP. In 2010 only 11% of respondents had
logues (Halford et al., 2011a,b). The survey was addressed to                           heard of voluntary instruments such as Codes of Conduct
nursery professionals, public green managers, private manag-                            on IAP. After having defined the basic principle of a CoC,
ers (landscape architects and garden contractors) and garden-                           61% of nursery professionals and 73% of private managers
ers. A total of 634 answers were collected and analysed to                              claimed that they would agree to endorse such a Code.
gain an overview of the baseline situation.                                             Horticulture professionals therefore expressed a strong will-
   Results showed that 93% of terrestrial and aquatic IAP                               ingness to participate in programs designed to prevent the
were still available in nurseries and that 67% of terrestrial                           spread of IAP. Such a trend was already observed in a pre-
IAP were mentioned in catalogues (Fig. 3). Invasive trees                               vious study (Vanderhoeven et al., 2011).


                                    42 42
                     40                     38 38
     Occurence (%)

                     30                                       28
                                                                   27 27
                                                                           23 23
                     20                                                                      18
                     10                                                                                     8
                                                                                                                7   6   5   5   5   4   3   3   3   2

Fig. 3 Occurrence of terrestrial IAP in horticultural catalogues in Belgium (n = 146 catalogues) in 2010. Black bars: black list species; Grey bars:
watch list species.

ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
4     M. Halford et al.

                                                                     version of the Code is available at The
The drafting of the Belgian Code of conduct
                                                                     measures proposed are in line with the recommendations
on IAP: a consultation process
                                                                     provided by Heywood & Brunel (2011).
                                                                        The horticultural sector considered that the good prac-
A step by step process
                                                                     tices proposed in the Belgian CoC were realistic and easy
The Belgian CoC was developed in consultation with repre-            to apply in horticultural firms and/or in public departments
sentatives of the horticultural sector (i.e. horticulture profes-    responsible for planting. Codes of conduct should not
sionals and representatives of the main horticultural                include an excessive number of measures or recommenda-
federations/associations in Belgium), administrative bodies          tions. During the final survey carried out at the end of the
responsible for environment and the scientific community             project (see below), monitoring of the Code showed that
(i.e. scientists specialized in invasion biology). Consultation      three measures (out of five) were mostly cited by horticul-
processes can be powerful tools to resolve environmental             ture professionals who had signed the Code (Halford et al.,
problems, find a common ground and achieve a broad con-              2013). In the United States, 83% of nursery professionals
sensus with actors from different disciplines. They can be           reported having participated in at least one preventive mea-
an efficient communication method for collaborative prob-            sure included in the St. Louis voluntary Codes of conduct,
lem solving. The consultation was organized through round            with an average of 2.4 out of 7 (Burt et al., 2007).
table discussions gathering a representative sample of horti-
culture professionals. Two working groups were consulted:
                                                                     The ‘consensus list’ and the ‘communication list’
(1) ornamental plant producers and sellers (including nurs-
ery professionals and managers of garden centers) and (2)            The key measure of the Belgian Code is the limitation of
ornamental plant users (including public green managers,             use of IAP (i.e. ban from sale or planting). Negotiations
landscape architects, garden contractors and representatives         enabled a list of 28 invasive alien plants to be defined
of botanical gardens). Working groups were separated in              (including varieties, hybrids and cultivars derived from
order to facilitate an agreement between participants prac-          those species) to be withdrawn from sale and/or planting.
ticing similar activities. Ten meetings were organized from          This list was unanimously approved by vote from horticul-
November 2010 until July 2011, gathering a total of 70 par-          ture professionals gathered in working groups. A consensus
ticipants. Round table discussions were conducted at the             was therefore reached among participants. That is why this
initiative of the AlterIAS team to identify workable mea-            list was called the ‘consensus list’. The concept of building
sures to reduce trade and use of IAP in Belgium and                  consensus list is now cited abroad, especially in France
develop a CoC taking into account both the environmental             (Mandon-Dalger et al., 2013). The consensus list of the
impact and the economic value of IAP. The consultation               Belgian Code represents 43.8% of the total number of inva-
with the horticulture sector was necessary to propose practi-        sive plants presently included in the Harmonia information
cal recommendations which were acceptable for the profes-            system (i.e. 64 plant species).
sion. The Belgian CoC was therefore the result of a trade-              A ban on the production, sale and planting of all invasive
off taking into consideration the invasiveness of species            plants used as ornamentals was impossible within the frame
(i.e. environmental impacts) and socio-economic factors              of a voluntary approach. Restriction of use was accepted
related to ornamental uses.                                          for (1) widespread and highly invasive plant species
   The consultation process was planned in several steps             (e.g. Fallopia japonica, Heracleum mantegazzianum, Prunus
including the presentation of the environmental issue, the           serotina) and (2) species of low or medium economic value
negotiation of measures and the definitive approbation of            (e.g. Duchesnea indica, Bidens frondosa, Mimulus guttatus).
the Code. Such a progressive process is in line with the             However, restriction of use was refused for species of high
process model in six steps referred to in Ten Brink (2002)           economic importance (e.g. Buddleja davidii, Amelanchier
for preparing voluntary approaches. The consultation pro-            lamarckii, Robinia pseudoacacia, Prunus laurocerasus)
cess carried out in Belgium was successful: the Code was             which were highly appreciated for gardening and landscape
unanimously approved by horticultural organizations and              planting. Invasive species that were invading only specific
horticulture professionals after 9 months of negotiation.            habitats (e.g. Rosa rugosa in coastal dunes or Robinia
The content of the Code is characterized by several articles         pseudoacacia on rocky slopes or dry grasslands) or had a
specifying the target audience, the geographical scope of            limited or unknown environmental impact (i.e. ‘watch list’
the instrument, the revision process, etc. The nature of the         species and/or species at the very beginning of the inva-
commitment consists of five good practices: (1) keep                 sion process) were hardly perceived as detrimental by
informed about the list of invasive plants in Belgium; (2)           horticulture professionals. Invasive alien plants excluded
stop planting and/or selling some invasive plants in Bel-            from the consensus list were therefore included in a second
gium (the ‘consensus list’ – see below); (3) disseminate             list called the ‘communication list’ (annex II of the Code).
information on invasive plants to customers or citizens; (4)         No restriction of use was recommended in the Code for
promote the use of non-invasive alternative plants and (5)           those species. Communication and recommendations on
take part in early detection of new invaders. The final              planting have been proposed in order to limit their use near

                                                       ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
The Belgian Code of conduct on invasive plants                      5

habitats of high conservation value. The communication on                    Table 4 Number and percentage of consensus list species and
annex II species was defined with a message coupled with a                   communication list species according to the economic value assessed
pictogram which could be used in horticultural catalogues.                   from the initial survey (Halford et al., 2011a,b)

   Only species of the black list and the watch list from the
                                                                                                  High           Medium          Low            Total
Harmonia information system (i.e. 57 species) were negoti-
ated during the consultation process. The alert list (i.e. spe-                                   Nb     %       Nb   %          Nb    %        Nb      %
cies not yet naturalized in Belgium) was not discussed. In
                                                                             Consensus list        0       0.0   12       70.6   16      69.6   28       49.1
Tables 1–3 the consensus list and the communication list
                                                                             Communication        17     100.0    5       29.4    7      30.4   29       50.9
are characterized according to different criteria from the                    list
Harmonia information system (i.e. plant type, environmen-                    Total                17     100     17   100        23    100      57      100
tal impact and invasion stage).
   Among the 57 invasive species discussed, the consensus
list represents 44% of terrestrial plants and 67% aquatic
                                                                             list are characterized according to the economic value.
plants. The consensus list includes 60% of the black list
                                                                             Species were assigned to three classes of economic impor-
plants and 37% of the watch list plants. Finally, the list is
                                                                             tance based on the answers collected from the initial survey
characterized by 50% of the widespread invasive alien plants,
                                                                             (Halford et al., 2011a,b): high economic value (IAP consid-
48% of the invasive alien plants located in restricted areas
                                                                             ered as economically important by more than 5% of nursery
and 50% of the invasive plants distributed in isolated popu-
                                                                             professionals), moderate economic value (IAP considered as
lations. In Table 4, the consensus list and the communication
                                                                             economically important by 1–5% of nursery professionals)
                                                                             and low economic value (IAP that were not considered as
Table 1 Number and percentage of consensus list species and
                                                                             economically important by nursery professionals).
communication list species according to the plant type defined in the           No species of high economic value are included in the
Harmonia information system                                                  consensus list, which is characterized by 71% of invasive
                                                                             alien plants with a medium economic value and 70% of
                        Terrestrial      Aquatic                             species with a low economic value.
                        plant            plant             Total

                        Nb      %        Nb       %        Nb      %         The need for an attitude encouraging dialogue and
Consensus list          20       44.4     8        66.7    28       49.1
Communication list      25       55.6     4        33.3    29       50.9     During the consultation, discussions about the annex I
Total                   45      100      12       100      57      100
                                                                             (i.e. the consensus list) and annex II (i.e. the communica-
                                                                             tion list) of the Code were the most debated. Discussions
Table 2 Number and percentage of consensus list species and                  between scientists and horticulture professionals were
communication list species according to the environmental impact             sometimes difficult. Indeed, there is conflict in values
defined in the Harmonia information system                                   between those who enjoy the benefits of exotic plants
                                                                             and those who are concerned about the harm such plants
                                                                             may cause (Reichard, 2004). Objections were frequently
                        High impact      impact
                                                                             addressed about controversial issues such as the classifi-
                        (black list)     (watch list)      Total
                                                                             cation of invasive species in a black list/watch list
                        Nb      %        Nb       %        Nb      %         system (concept not always positively perceived or easily
                                                                             understood outside a scientific audience); the invasiveness
Consensus list          18       60.0    10        37.0    28       49.1
                                                                             of species and derived cultivars; the feeling that scientists
Communication list      12       40.0    17        63.0    29       50.9
Total                   30      100      27       100      57      100       or ecologists have exaggerated/generalized the problem
                                                                             from a few widespread species; ‘native expanding plants’

Table 3 Number and percentage of consensus list species and communication list species according to the invasion stage defined in the Harmonia
information system

                                Widespread                      Restricted area                    Isolated populations                Total

                                Nb            %                 Nb                %                Nb             %                    Nb               %

Consensus list                  10             50.0             11                 47.8             7              50.0                28                49.1
Communication list              10             50.0             12                 52.2             7              50.0                29                50.9
Total                           20            100               23                100              14             100                  57               100

ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
6     M. Halford et al.

often considered as weeds (sensu Richardson et al.,                      proposed, the plants must present no risk of becoming inva-
2000)1 and as “real” invasive plants in nurseries; the lack              sive in the future. Such a risk assessment is extremely hard
of self-regulation tools on IAP in neighbouring countries                to evaluate with absolute certainty. To limit those risks,
which export/import plants to/from Belgium. The inva-                    most ecologists adopt a precautionary principle which is in
siveness of some species highly appreciated as ornamen-                  favour of the idea of promoting native plants only. This
tals and classified as invasive by scientists was                        point of view is not always shared by horticulture profes-
sometimes refuted. In England a similar mismatch was                     sionals. The feasibility of promoting only native plants
observed between the species that DEFRA (Department                      depends on the country, the cultural and/or economical con-
for Environment Food and Rural Affairs) considered to                    text. In some regions (e.g. South Africa, Reunion islands)
be invasive and the view of the trade. In many cases, a                  native plants can be exclusively proposed. It is culturally
majority of the trade did not consider the plants in ques-               accepted. This is probably due to the diversity of native
tion to be potentially invasive (Creative Research, 2009).               plants available in these regions (compared to Western
In Belgium, some nursery professionals strongly disagreed                European countries where the diversity of native species
with the point of view of scientists when they learnt that               used as ornamentals is rather poor). In other cases and/or
ornamental plants traditionally cultivated for years (for                countries, the exclusive promotion of native plants may
examples species of the genus Rhododendron, Aster,                       provoke opposition from the horticulture industry because
Rosa, Cotoneaster) were listed as invasive by scientists,                most ornamental plants available in the market are exotic
while those species were not invasive in some regions                    species useful for gardening or landscape planting. Most of
where they are cultivated. Horticulture professionals urged              these pose no problem for the environment (see the
invasion ecologists to better consider local climatic con-               Williamson’s tens rule stating that only one alien plant may
texts and regional conditions.                                           become invasive out of 1000 species introduced). In
   When such opposition emerges, it is recommended to lis-               Belgium, the promotion of alternative plants would have
ten to the different points of view, try to understand the               failed if only native plants were exclusively recommended
opinions expressed and the underlying reasons for these in               as alternatives in the CoC. Horticulture professionals
order to find a common ground for a solution by starting                 involved in the Code were therefore free to choose and pro-
with statements on which everybody agree. The point of                   pose native or non-native alternative plants to customers.
view of the ornamental sector must be heard and under-
stood. One frequently made mistake in communication con-
                                                                         The promotion of the Code
sists of trying to convince stakeholders rather than listening
and taking on board their points of view, understanding                  Drafting a CoC was only one step of the process. The next
their motivations and how they relate to the issue (Hesse-               step consisted of implementing and promoting the Code
link et al., 2007). It must also be understood that restric-             within the horticulture sector in order to seek participation
tions on use will be accepted for certain invasive species               from horticulture professionals throughout the country. As
only. It is more difficult to withdraw species of high eco-              recommended by Heywood & Brunel (2011), communica-
nomic value on a voluntary basis. Indeed, a basic principle              tion campaigns are required in the implementation of a
of any voluntary scheme states that the firms involved must              CoC. Coverage, publicity and information-oriented provi-
perceive some gain or benefit (or at least no net loss) from             sions feature among the criteria needed for a successful vol-
participation (Alberini & Segerson, 2002).                               untary scheme (OECD, 2003). Several Codes or charters on
                                                                         IAP have failed to reach the target audience due to a lack
                                                                         of communication and promotion.
Alternative plants: native or non-native?

The use of non-invasive alternative plants (concept of
                                                                         The ‘Plant different’ campaign
‘green list’) was considered as a positive solution which (1)
counterbalances the restriction of use by proposing substi-              A specific communication campaign (entitled ‘Plant differ-
tute plants and (2) has the potential to create a new market             ent’) was planned for the promotion of the Code in Belgium.
which could be profitable for the horticulture industry. In              Adapted communication materials were prepared. Communi-
Belgium such a measure was easily accepted and positively                cation materials included the project folder (75 000 copies
perceived under the condition that horticulture professionals            printed), the Code of conduct folder (65 000 copies), a poster
were free to propose alternative plants (i.e. native or exo-             (1000 copies) and a brochure on alternative plants (40 000
tic). Indeed there is a debate about the species that should             copies). Examples of communication materials are provided
be recommended as alternatives. If exotic species are                    in Fig. 4. A subscription process was implemented. The Bel-
                                                                         gian Code can be signed ‘manually’ (paper version) or ‘elec-
1                                                                        tronically’ (online registration in a ‘Partner database’
 According to Richardson et al. (2000) weeds are plants (not necessar-
ily alien) that grow in sites where they are not wanted and which usu-   available on the AlterIAS website). The materials were sent
ally have detectable economic or environmental effects (synonyms:        by post to horticulture professionals registered in the
plant pests, harmful species; problem plants)                            database. Signed Codes involve a voluntary and moral

                                                           ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
The Belgian Code of conduct on invasive plants               7

Fig. 4 Examples of communication materials produced during the Code of Conduct promotion campaign. From left to right: the CoC logo, folder
and poster.

commitment from an organization or a firm to implement the                the Code. Such actions can be considered as the first step of
agreement. Such Codes are different from codes of conduct                 the promotion strategy. Communication tools most fre-
or codes of practice that give guidelines on good practices               quently used by the target audience were identified in the
and where no commitment is taken (Sonigo et al., 2011).                   final survey (Halford et al., 2013). However general com-
   The Code was officially launched in September 2011                     munication actions were not efficient in obtaining new sig-
during ‘signature ceremonies’ gathering horticultural federa-             natories to the Code. Direct consultations were needed to
tions, policy-makers and partners of the AlterIAS projects.               convince stakeholders to endorse the Code.
All horticultural federations/associations officially signed
the Code during these events. The press was invited in
                                                                          The importance of conveying positive messages to the
order to provide media coverage. Several articles were pub-
                                                                          horticultural sector
lished in newspapers with a wide audience. An active pro-
motion was required in order to (1) inform horticulture                   The communication strategy to promote the Code was
professionals and gardeners about this new instrument                     based on positive messages focused on bringing about solu-
(among the other charters, labels or programs dedicated to                tions instead of highlighting the problems. It is recom-
environmental protection which are already under applica-                 mended to promote a Code with engaging messages asking
tion in Belgium) and (2) encourage/convince them to adopt                 for behaviour change and participation in biodiversity con-
it. Different communication actions were used for the pro-                servation. The use of alarming terms with exaggerated
motion of the Code. During this campaign, the AlterIAS                    impacts on biodiversity, military metaphors or logo’s
project (1) published 33 articles in regional or local press              focused on “don’t” messages are not appropriate. In Bel-
and 45 articles in federation journals or horticulture maga-              gium, even terms like ‘black list species’ were negatively
zines; (2) organized 70 conferences or information sessions;              perceived by most nursery professionals who have culti-
(3) participated in 45 horticultural events, 8 TV reports and             vated some of these ‘black list’ plants for years. The ‘black
7 radio reports. There was limited involvement in the Code                list/watch list’ terminology should be reserved for use
(i.e. limited signatories from horticulture professionals and             within the scientific community where these terms are
gardeners) without appropriate communication. Above all,                  accepted in risk assessment methods. Horticulture profes-
promotion required direct consultation with horticulture                  sionals often felt that negative communication was aggres-
professionals and public green managers (via e-mails, let-                sive and irritating which re-enforced the feeling of being
ters, phone calls, face-to face interviews and discussions,               guilty instead of encouraging positive solutions.
contacts during meetings or information sessions, etc.). All
professionals contacted were registered and followed-up by
                                                                          Results and changes of attitudes
the AlterIAS team. The success rate of direct consultation
was estimated to be about 23% (i.e. among 426 horticulture                On December 2013 (closing date of the AlterIAS project),
professionals directly contacted by the AlterIAS team, 99                 1022 stakeholders had signed the Code and were regis-
have signed the Code).                                                    tered in the CoC database. The stakeholders included 494
   The promotion of the Code required specific human                      horticulture professionals, 476 gardeners and 52 organiza-
resources (2.5 full-time equivalents during 2 years) fully                tions. The following categories of horticulture professionals
dedicated to communication actions and direct consultation.               were involved: 242 nursery professionals (producers, sell-
General communication actions (articles in press or in                    ers, wholesalers and selling points of garden centers); 150
federation journals, dissemination of folders and brochures,              public departments (cities, municipalities and provinces); 28
etc.) were efficient in informing the target audience about               landscape architects; 52 garden contractors and 6 botanical

ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
8                                   M. Halford et al.

gardens. Organizations included horticultural federations                                     2. Horticulture professionals were better aware of the eco-
and environmental agencies. A positive dynamic of involve-                                        logical issue related to invasive alien plants. When
ment was observed over time (Fig. 5).                                                             defining invasive alien plants, the percentage of respon-
   Involvement rates were estimated by comparing the num-                                         dents who spontaneously cited negative impact on biodi-
ber of professionals involved with the number of members                                          versity increased by 17% during the project.
affiliated in main horticultural federations. Data were com-                                  3. The availability of information has increased by 30%: in
pleted with a survey dedicated to the monitoring of the                                           2013, 88% of horticulture professionals have been
Code. Involvement rates were estimated between 10% to                                             informed on invasive alien plants (compared to 59% in
30% for horticulture professionals (nursery professionals,                                        2010). The need for information has been fulfilled: most
garden contractors and landscape architects), 25–35% for                                          horticulture professionals (64%) felt well enough
municipalities, 90% for provinces and 21% for botanical                                           informed about invasive alien plants in 2013 (compared
gardens. Those results are encouraging but the Code will                                          to only 34% in 2010).
require more than 2 years to be widely adopted by the hor-                                       However no significant change of attitudes was observed
ticultural sector. Efforts must be pursued to better mobilize                                 for gardeners. On top of that no massive endorsement was
horticulture professionals and increase the number of part-                                   observed: 24% of gardeners had heard of the Belgian CoC
ners in the future. Voluntary schemes must be planned with                                    and 23% claimed they had endorsed it. Despite communi-
a long-term perspective in order to progressively reach a                                     cation efforts, only a small proportion of gardeners were
high proportion of stakeholders.                                                              reached by the CoC promotion campaign. The information
   In 2013, a final survey was performed in order to evalu-                                   delivered was probably ‘diluted’ among the mass of peo-
ate (1) the changes of attitudes of horticulture professionals                                ple to reach. Indeed millions of people are gardeners in
and gardeners (i.e. evolution of the level of knowledge on                                    Belgium. Communication campaigns targeting the general
IAP, need for information, awareness, concern, etc.) and (2)                                  public at a national scale require specific resources,
the perception of the CoC by horticulture professionals                                       including a frequent use of mass media and new web-
(Halford et al., 2013). A total of 641 surveys were col-                                      related tools (social networks, i-phone applications, etc.).
lected. Changes of attitudes were quantified by comparing                                     A specific communication campaign is required for
the results with the initial survey carried out in 2010. Posi-                                gardeners.
tive results were observed for horticulture professionals:                                       Thanks to communication efforts, the knowledge of volun-
1. Communication has increased the level of knowledge of                                      tary approaches such as Codes of conduct has considerably
    this target group: in 2013, 80% of nursery professionals                                  increased between 2010 and 2013. In 2013, 56% of nursery
    had a correct level of knowledge of the concept of inva-                                  professionals, 73% of public green managers working in
    sive plants (compared to 60% in 2010). In addition                                        municipalities and 69% of private managers (landscape
    results showed a better knowledge of the list of invasive                                 architects, garden contractors) had heard of the Code. In the
    alien plants in Belgium: 28 invasive alien plants were                                    United States, only 7% of nursery professionals had heard of
    correctly cited as examples by respondents in 2013                                        the St. Louis Voluntary Codes of Conduct 3 years after its
    (compared to 17 species in 2010).                                                         ratification (Burt et al., 2007). In England, 46% of nursery


                                   1000           Gardeners                                                                                                 52
 Number of stakeholders involved

                                                  Horticulture professionals                                                        46
                                                                                                            44                     406


                                                                          33                                                                               494
                                    200                                                                    397
                                                        26                118

Fig. 5 Evolution over time of the number of stakeholders involved in the Belgian Code of conduct.

                                                                                ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
The Belgian Code of conduct on invasive plants        9

retailers were aware of the Horticultural Code of practice            invasive species (i.e. the consensus list species) could be
launched by DEFRA in 2005 (Creative Research, 2009).                  withdrawn from sale or planting on a voluntary basis.
   In Belgium, the final survey revealed that the underlying          However such a measure is effective under the condition
reasons for adopting the Belgian Code were (1) the protec-            that a high number of horticulture professionals are
tion of the environment, (2) the positive publicity for the           involved in the Code. Despite a positive dynamic of
‘green image’, (3) the support by federations/organizations           involvement observed in Belgium, efforts must be pur-
and (4) the ease of implementation. The support from fed-             sued to better mobilize the horticultural sector. Long-term
erations and the fear of restrictive regulation was an impor-         objectives must be defined. Voluntary approaches should
tant driver for nursery professionals, especially in Flanders         be considered as a first step that, if not successful (i.e. if
(i.e. Northern Belgium). This confirms the need to prepare            the objectives are not reached), may lead to regulation.
a Code in consultation with the horticultural sector in order         Credible regulatory threat must be addressed by public
to ensure the support from federations/associations (which            authorities.
in turn is a strong argument for endorsement for nursery                 On the other hand results from the final survey suggest that
professionals). The Code was welcomed differently in dif-             communication campaigns and CoC were effective in raising
ferent regions. Nursery professionals from Flanders were              awareness when the target audience was clearly defined. This
more skeptical. The sector is economically more developed             was the case with horticulture professionals affiliated in fed-
in this region (90–95% of the production of ornamental                erations. Considering the lessons learned from the AlterIAS
plants in Belgium is located in Flanders). The skepticism             project, the following recommendations could be proposed to
reflected the fear of negative impact on the business consid-         improve the effectiveness of CoC in the future:
ering the restriction of use recommended in the Code.                 1. Codes with individual commitment should be preferred.
However such a fear seems unjustified. The final survey                   Signed Codes involve a voluntary and moral commit-
showed that the measures proposed in the Belgian Code are                 ment from an organization or a firm to implement the
easy to implement and not restrictive. Only 11% of horti-                 agreement. Codes without individual commitment are
culture professionals involved in the Code had encountered                expected to have limited effectiveness because there is
problems with its implementation and only 8% consider it                  no trace of the commitment. A subscription process
had a negative impact on their activities (Halford et al.,                must be set up, with a multi-stakeholder approach
2013). On the other hand, the main reasons for having not                 involving the main actors from the horticultural sector.
adopted the Code were (1) the lack of information (i.e. hor-          2. Codes should include measures of restriction of invasive
ticulture professionals were not informed about the Code)                 species (i.e. ban from sale/planting) which are expected
and (2) the lack of availability (i.e. horticulture profession-           to be more effective for reducing deliberate introduc-
als had no time/were too busy). In 2013, 44% of nursery                   tions of invasive alien plants. In this case, the list of
professionals had not heard of the Code. This underlines                  species targeted must be clearly defined in the Code.
the need to continue the Code of conduct promotion                        Such a list must be built in consultation with the horti-
campaign.                                                                 cultural sector (i.e. concept of consensus list). Restric-
   The knowledge of measures recommended in the Belgian                   tions must be compensated for by the promotion of non-
Code was moderate. Three measures (out of 5) were most                    invasive alternative plants which are profitable for the
frequently cited: (1) ‘stop the sale and/or planting of inva-             horticulture industry.
sive alien plants’, (2) ‘disseminate information on invasive          3. Communication campaigns must be considered as a nec-
alien plants’ and (3) ‘promote the use of alternative plants’.            essary phase of the implementation of a CoC. There is
Measures implying restriction of use of a species (‘stop the              limited involvement without appropriate communication.
sale and/or planting) were quoted by 81% of nursery pro-                  Communication with the horticultural sector must be
fessionals, 60% of public green managers and 46% of pri-                  focused on positive messages highlighting realistic solu-
vate managers. All horticulture professionals (100%)                      tions and encouraging participation in the program.
involved in the Code had disseminated information on inva-               The question of monitoring (i.e. inspection) of voluntary
sive plants to customers or the general public. The commu-            approaches on IAP remains an open question. In Belgium
nication means most frequently used were (1) ‘distribution            no data were collected on this specific point. The progress
of folders and brochures’; (2) ‘display of the Code of                of the Code was monitored through (1) the partner data-
conduct poster’ and (3) ‘communication on annex II species            base and (2) a survey. No inspections were conducted
(i.e. the communication list)’.                                       within firms involved in the Code in order to check if
                                                                      invasive alien plants which were the object of a restriction
                                                                      (i.e. the consensus list) were really withdrawn from sale/or
Conclusion and perspectives
                                                                      planting. In the Netherlands, a monitoring procedure was
Codes of conduct on IAP have two main goals: (1) to                   implemented within the framework of the negotiated agree-
reduce deliberate introductions of invasive plants and (2)            ment on aquatic invasive alien plants. The monitoring was
to increase the level of awareness-raising. The first                 part of the agreement (with no penalties if disregarded).
objective was partially reached in Belgium. Only some                 Checks were carried out by officers of the Food and

ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
10     M. Halford et al.

Consumer Product Safety Authority (NVWA). Positive                  avec des representants du secteur des plantes ornementales,
results were obtained with respect to the withdrawing of            des autorites publiques, ainsi que de la communaute
plants from sale. Most nursery professionals engaged in the         scientifique. Ce Code a ete mis en avant dans l’ensemble
Code respected the commitment (almost 100 %), Quanti-               du pays avec une campagne de communication specifique «
fied data were collected by Verbrugge et al. (2013). This           Plantons autrement ». Gr^ace aux efforts de communication,
demonstrates that voluntary instruments can efficiently con-        une dynamique d’implication positive a ete observee au
tribute to reduce the sale of invasive plants on a large            cours du temps. Des etudes ont ete menees pour evaluer les
scale (i.e. at a national scale). However the results obtained      changements d’attitudes et la perception du Code par son
in the Netherlands may not necessarily be applicable to the         public cible. Des resultats positifs ont ete obtenus aupres
work in other countries and results may depend on the type          des professionnels de l’horticulture. Le Code demandera
of voluntary approaches implemented. Other results could            cependant plus de temps pour ^etre adopte de maniere plus
have been reached with Codes that stakeholders can sign             large par le secteur ornemental en Belgique.
knowing that it will not be checked. The feasibility of car-
rying out such a check also depends on the number of
                                                                    Дoбpoвoльный Кoдeкc пoвeдeния в
stakeholders involved and the resources available within
                                                                    oтнoшeнии инвaзивныx чyжepoдныx pacтeний
the institution in charge of the monitoring (L. N. H. Verb-
                                                                    в Бeльгии: peзyльтaты и ypoки, извлeчeнныe
rugge, pers. comm., 2013). The Dutch agreement targeted
                                                                    из пpoeктa AlterIAS LIFE+
a limited number of nursery firms specialized in aquatic
plants. Officers from the NVWA were able to monitor                 Дoбpoвoльныe пoдxoды нeдaвнo иcпoльзoвaлиcь в
them all.                                                           ceктope caдoвoдcтвa для paбoты c интpoдyкциeй и
   The Code implemented in Belgium within the framework             pacпpocтpaнeниeм чyжepoдныx инвaзивныx pacтeний. B
of the AlterIAS LIFE+ project must be considered as a first         Бeльгии пepвыe кoдeкcы пoвeдeния были paзpaбoтaны в
step of a progressive awareness-raising approach which will         paмкax пpoeктa AlterIAS LIFE+ «Инфopмaция и
continue in the future. The instrument will still be operational    Кoммyникaция»,      нaцeлeннoгo     нa     пoвышeниe
once the project is over. An After LIFE Communication Plan          ocвeдoмлeннocти пpoфeccиoнaлoв плoдoвoдcтвa и
(2014–2018) is being implemented to ensure the continuation         caдoвoдoв в oтнoшeнии пpoблeмы инвaзивныx pacтeний.
of the Code. A revision process is planned every 3 years. The       Бeльгийcкий Кoдeкc был пoдгoтoвлeн в xoдe
revision will be taken in hand by regional administrations,         кoнcyльтaций c пpeдcтaвитeлями ceктopa дeкopaтивныx
while horticultural organizations will continue the promotion       pacтeний, opгaнoв гocyдapcтвeннoй влacти и нayчнoгo
to horticulture professionals.                                      cooбщecтвa.     Блaгoдapя    нayчнo-пpocвeтитeльcкoй
                                                                    кaмпaнии пoд нaзвaниeм «Caжaй c oглядкoй», кoдeкc
                                                                    pacпpocтpaнялcя пo вceй cтpaнe, и в тeчeниe дoлгoгo
                                                                    вpeмeни     oтмeчaлacь    пoлoжитeльнaя      динaмикa
The authors are grateful to the different funding bodies sup-       вoвлeчeннocти. Были пpoвeдeны oпpocы, пoзвoляющиe
porting the AlterIAS project, i.e. the DG Environment of            oцeнить измeнeния пcиxoлoгичecкиx ycтaнoвoк и
the European Commission and the different federal and               вocпpиятия Кoдeкca цeлeвoй ayдитopиeй пpoeктa. B
regional agencies in charge of biodiversity conservation in         oтнoшeнии     пpoфeccиoнaлoв    плoдoвoдcтвa     были
Belgium: the Federal Public Service on Health, Food Chain           дocтигнyты    пoлoжитeльныe     peзyльтaты.    Oднaкo
Safety and Environment, Agentschap voor Natuur en Bos               пoтpeбyeтcя бoльшe вpeмeни для шиpoкoгo пpинятия
(Flanders), Brussels Environment (Brussels) and the Direc-          Кoдeкca ceктopoм дeкopaтивныx pacтeний в Бeльгии.
tion Generale de l’Agriculture, des Ressources Naturelles et
de l’Environnement (Wallonia).
                                                                    Alberini A & Segerson K (2002) Assessing voluntary programs to
Code de conduite volontaire sur les plantes
                                                                      improve environmental quality. Environmental and Resource
envahissantes en Belgique: re sultats et retour                      Economics 22, 157–184.
     rience du projet AlterIAS LIFE+
d’expe                                                              Burt JW, Muir AA, Piovia-Scott J, Veblen KE, Chang AL, Grossman
                                                                      JD et al. (2007) Preventing horticultural introductions of invasive
Les approches volontaires ont ete recemment utilisees dans
                                                                      plants: potential efficacy of voluntary initiatives. Biological Invasions
le secteur horticole pour limiter l’introduction et la                9, 909–923.
dissemination des plantes exotiques envahissantes. En              Creative Research (2009). Wildlife Management and Invasive Non-
Belgique, le premier Code de conduite a ete mis au point            Native Species. Report of Research Findings among the General
dans le cadre du projet AlterIAS, un projet LIFE+ «                   Public, Anglers and the Horticultural Retail Trade (Volume 1).
Information & Communication » visant a favoriser la prise            London (UK). 147 pp.
de conscience des questions liees aux plantes envahissantes        Dehnen-Schmutz K, Touza J, Perrings C & Williamson M (2007) The
                                                                      horticultural trade and ornamental plant invasions in Britain.
chez les professionnels de l’horticulture et chez les
                                                                      Conservation Biology 21, 224–231.
jardiniers. Le Code belge a ete prepare en concertation

                                                      ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
The Belgian Code of conduct on invasive plants                11

EPPO (2011) EPPO Reporting Service, no 6 2011/144. Results of the               Reichard SH (2004) Conflicting values and common goals: codes of
  survey on the implementation of the Code of conduct on                          conduct to reduce the threat of invasive species. Weed Technology
  horticulture and invasive alien plants in European and Mediterranean            18, 1503–1507.
  countries.          Richardson DM, Pysek P, Rejmanek M, Barbour MG, Panetta FD &
  (accessed on 7 March 2013).                                                     West CJ (2000) Naturalization and invasion of alien plants: concepts
Halford M, Heemers L, Mathys C, Vanderhoeven S & Mahy G (2011a)                   and definitions. Diversity and Distributions 6, 93–107.
  Socio-Economic Survey on Invasive Plants and Ornamental                       Roush R, Groves RH, Blood K, Randall RP, Walton C, Thorp J &
  Horticulture in Belgium, Final report. University of Liege Gembloux            Csurhes S (1999) Garden Plants Under the Spotlight. An Australian
  Agro Bio-Tech, Gembloux (BE), 29 pp.                                            Strategy for Invasive Garden Plants. Cooperative Research Centre
Halford M, Mathys C, Heemers L, Vanderhoeven S, Branquart E, van                  for Weed Management Systems & Nursery Industry Association of
  Gossum H et al. (2011b). The Code of Conduct on Invasive Plants in              Australia, Adelaide (Australia).
  Belgium. Plant Different. Final version revised in January 2013.              Scalera R (2010) How much is Europe spending on invasive alien
  University of Liege Gembloux Agro Bio-Tech, Gembloux (BE). 11 pp.              species? Biological Invasions 12, 173–177.
Halford M, Heemers L, Dierickx M, Van Wesemael D, Mathys C &                    Segers H & Branquart E (2010) ISEIA, a Belgian non-native species
  Mahy G (2013). Perception of Invasive Alien Plants by the                       protocol. In (Eds Segers H & Branquart E) Proceedings of the
  Horticultural Sector in Belgium: the AlterIAS Project and the Changes           Science Facing Aliens Conference, pp. 11–18. Brussels (BE).
  of Attitudes after Four Years of Awareness-Raising. Final report.             Shine C, Kettunen M, Genovesi P, Essl F, Gollasch S, Rabitsch W
  University of Liege Gembloux Agro Bio-Tech, Gembloux (BE). 31 pp.              et al. (2010) Assessment to Support Continued Development of the
Hesselink FJ, Wendy Goldstein W, Van Kempen PP, Garnett T & Dela                  EU Strategy to Combat Invasive Alien Species. Final Report for the
  J (2007) Communication, Education and Public Awareness (CEPA):                  European Commission. Institute for European Environmental Policy
  A Toolkit for National Focal Points and NBSAP Coordinators, 310                 (IEEP), Brussels (BE). 298 pp.
  pp. Secretariat of the Convention on Biological Diversity and IUCN,           Sonigo P, Turbe A, Berman S & Reilly K (2011) A Comparative
  Montreal (CA).                                                                  Assessment of Existing Policies on Invasive Species in the EU
Heywood V, & Brunel S (2011). Code of Conduct on Horticulture and                 Member States and in Selected OECD Countries, Final report for the
  Invasive Alien Plants. Nature and environment no 162, Council of                European Commission Bio Intelligence Service, Paris (FR). 258 pp.
  Europe, Strasbourg (FR). 95 pp.                                               Ten Brink (2002). Voluntary Environmental Agreements: Process,
Mandon-Dalger I, Guerin M & Provendier D (2013). Concertation entre               Practice and Future Use, 470 pp. Greenleaf Publishing, Sheffield
  acteurs de la conservation et des filieres du vegetal et notion de liste     (UK).
  de consensus. In : 3eme conference sur l’entretien des espaces verts,       Vanderhoeven S, Piqueray J, Halford M, Nulens G, Vincke J & Mahy
  jardins, gazons, for^ets, zomes aquatiques et autres zones non                  G (2011) Perception and understanding of invasive alien species
  agricoles. Toulouse (FR), 15, 16, 17 octobre 2013.                              issues by nature conservation and horticulture professionals in
Moss W & Walmsley R (2005) Controlling the Sale of Invasive                       Belgium. Environmental Management 47, 425–442.
  Garden Plants: Why Voluntary Measures Alone Fail, 14 pp. World                Verbrugge LNH, Van den Born RJG & Leuven RSEW. (2013).
  Wide Fund for Nature Australia, Sydney (AU).                                    Evaluatie     Convenant       Waterplanten      2010-2013.   Reports
OECD (2003) Voluntary Approaches for Environmental Policy:                        Environmental Science no. 440. Radboud University, Nijmegen (NL).
  Effectiveness, Efficiency and Usage in Policy Mixes, 143 pp. OECD             Yi L, Zongming C, Smith WA, Ellis DR, Yongqin C, Xuelian Z et al.
  Publications Service, Paris (FR).                                               (2006) Invasive ornamental plants: problems, challenges and
Reichard SH & White P (2001) Horticulture as a pathway for invasive               molecular tools to neutralize their invasiveness. Critical Review in
  plant introductions in the United States. BioScience 51, 103–113.               Plant Sciences 23, 381–389.

ª 2014 The Authors. Journal compilation ª 2014 OEPP/EPPO, EPPO Bulletin 44, 1–11
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