Integrating invasive species policies across ornamental
horticulture supply chains to prevent plant invasions
Julia M. Touza
Mark van Kleunen
221The Bio-Protection Research Centre, Uncoln University, Canterbury, New Zealand
2Department of Agriculture, University of Sassari, Sassari, Italy
3Laboratoire d'Ecologie Alpine (LECA), University of Grenoble Alpes, Grenoble, France 4Laboratoire d'Ecologie Alpine (LECA), CNRS, Grenoble, France
5Centre for Agroecology, Water and Resilience, Coventry University, Coventry, UK 6Department of Botany and Biodiversity Research, University Vienna, Vienna, Austria 7Centre for Ecology and Conservation, University of Exeter Penryn Campus, Cornwall, UK
SCABI, Egham, UK
9Botanic Garden Meise, Meise, Belgium
101nstitute of Integrative Biology, Department of Environmental Systems Science, ETH Zurich, Zurich, Switzerland 11Centre for Invasion Biology, Department of Botany and Zoology, Stellenbosch University, Matieland, South Africa 12Department of Community Ecology, Helmholtz Centre for Environmental Research -UFZ, Halle, Germany 13Martin-Luther-University Halle-Wittenberg, Halle, Germany
14Ecology, Department of Biology, University of Konstanz, Konstanz, Germany
151nvasive Species Programme, South African National Biodiversity Institute, Kirsten bosch Research Centre, Claremont, South Africa 16lnstitute of Botany, Department of Invasion Ecology, The Czech Academy of Sciences, Pmhonice, Czech Republic
17Department of Ecology, Faculty of Science, Charles University, Prague, Czech Republic 18Senckenberg Biodiversity and Climate Research Centre, Frankfurt, Germany 19European and Mediterranean Plant Protection Organization, Paris, France 20Environment Department, University of York, York, UK
21lnstitute for Science, Innovation and Society, Radboud University, Nijmegen, The Netherlands 22Netherlands Centre of Expertise for Exotic Species, Nijmegen, The Netherlands
Correspondence Philip E. Hulme
1. Ornamental horticulture is the primary pathway for invasive alien plant in
troduc-tions. We critically appraise published evidence on the effectiveness of four policy
instruments that tackle invasions along the horticulture supply chain: pre-border
import restrictions, post-border bans, industry codes of conduct and consumer
2. Effective pre-border interventions rely on rigorous risk assessment and high
indus-try compliance. Post-border sales bans become progressively less effective when
alien species become widespread in a region.
Konstanzer Online-Publikations-System (KOPS)
3. A lack of independent performance
evaluation and of
public disclosure, limits the
uptake and effectiveness
and discourages shifts
consumer preference away from invasive alien
pathway associated with ornamental
ture requires government-industry
to fund effective pre- and
post-border weed risk assessments
that can be subsequently
supported by widely
adopted, as well as verifiable, industry
codes of conduct.
This will ensure producers
and consumers make in
in the face
better targeted public
educa-tion addressing plant invasions.
biological invasions, biosecurity, exotic, gardening, invasive species, legislation, non-native, nurseries, trade, weed
The global trade in ornamental nursery stock is the dominant path-way by which invasive alien plants have been introduced world-wide (Dodd. Burgman, McCarthy, & Ainsworth. 2015; Faulkner. Robertson, Rouget & Wilson, 2016; Jiang et al., 2011; Lambdon et al.. 2008: Lehan. Murphy, Thorburn, & Bradley, 2013; Rojas-Sandoval & Acevedo-Rodriguez, 2015). This is not surprising since the ornamental nursery trade (comprising commerce in finished, bareroot and seed-ling trees. shrubs, ground covers. grasses, vines and aquatic plants of sale size, bulbs and seeds) is largely built around commerce in alien plant species, their hybrids, cultivars and varieties (Drew, Anderson, & Andow, 2010). Alien species often represent a higher proportion than native species In terms of what is cultivated, the available stock in retail outlets and consumer purchases. For example, in both Great Britain and New Zealand, there is an order of magnitude greater num-ber of plant species In cultivation than native plant species in the wild (Armitage et al., 2016; Gaddurn. 1999). In the United States, alien spe-cies comprise as much as 80% of the stock held by nurseries (Brzuszek & Harkess, 2009; Harris, Jiang, Uu, Brian, & He, 2009) and account for up to 90% of nursery revenue (Kauth & Perez, 2011). While only a relatively small proportion of taxa escape cultivation, often less than 10% (Hulme, 2012), the sheer number of taxa cultivated results in the ornamental pathway being the main source of naturalized and invasive alien plant species in natural areas world-wide (Figure 1).
Annual sales of nursery stock amount to US $430 million in Canada (Agriculture-Canada 201S), US $500 million in Australia (PHA 2015), US $1,054 million in the United Kingdom (Defra 2016) and US $4,267 million in the United States (USDA 2014). Policymakers could there-fore argue that plant invasions are an unavoidable minor cost incurred to support an industry that delivers significant economic benefits and brings pleasure to millions of gardeners. But can appropriate policies be designed to target the ornamental nursery industry supply chain such that changes to operations to mitigate invasions will be most easy to implement, cost-effective and acceptable?
~o Naturalised •Invasive
sc: G> 40 E
FIGURE 1 The percentage of 450 alien plant species that are
listed as established or invasive in one or more regions of the world and that have been introduced through ornamental horticulture. The term invasive refers to an alien species established in natural or semi-natural ecosystems that Is an agent of change threatening native biodiversity. Data and definitions are from Weber (2003)
THE ORNAMENTAL PLANT
City/Local oouncils e.g. landscaping Local Govemment/NGOs e.g. restoration Higlway authorlies e.g. revegetation Imports
FIGURE 2 Schematic illustration of the ornamental nursery supply chain identifying the route of alien germplasm from import, through propagation, to retail and subsequent use. The size and shading of the arrows represent the relative magnitude of the flows between each component and are based on financial data from Great Britain (Barney, 2014). The domain of four major policy instruments across the supply chain is also depicted
integration in the industry results in organizations playing multiple roles in the supply chain. For example, botanic gardens not only im
-port new germplasm but they are often also involved in plant breeding as well as retail to the general public (Hulme, 2011).
Actors within the ornamental nursery industry have different motivations, knowledge of invasive plant species and enthusiasm for
market change (Humair, Kueffer, & Siegrist, 2014). Thus, while several
policies exist addressing plant invasions arising from ornamental
hor-ticulture (Barbier, Knowler, Gwatipedza, Reichard, & Hodges, 2013;
Reichard & White, 2001), they have seldom been viewed as an inte
-grated suite of options targeting different actors (Drew et al., 2010). Preventing the introduction or establishment of potentially invasive alien species is often the most cost-effective and environmentally desirable policy option to manage invasions (Keller, Lodge, & Finnoff, 2007). The ornamental industry supply chain can be used to assess
the merit of four major policy instruments targeting prevention: pre
-border import restrictions; post-border plant sales bans (both affecting breeders, propagators and producers); industry codes of conduct (ad
-opted by trade and public retail outlets); and tools to engender con
-sumer behavioural change through increased public awareness.
Two contrasting approaches have been developed to restrict the importation of invasive alien plant species: blacklists that treat all unlisted plant imports as innocent until proven guilty vs. whitelists
that view all unlisted plants as guilty until proven innocent (Dehnen
-Schmutz, 2011). Both New Zealand and Australia have adopted a stringent whitelist approach in which species not recorded on a per
-mitted list require evaluation through a formal weed risk assessment
procedure (Auld, 2012). European nations often promote blacklists as
a cost-effective means to limit the importation of invasive alien plants (Essl et al., 2011). Under these circumstances weed risk assessments are used to support the listing of species on blacklists. However, due
to the large number of ornamental species available for import, cost
of risk assessments and the frequent lack of consensus among stake
-holders in relation to the listing criteria, blacklists are rarely compre
-hensive and are generally less effective than a whitelist of permitted species (Hulme, 2015a).
Furthermore, without mechanisms to check compliance, particu
-larly in the face of increasing Internet trade in invasive alien species (Humair, Humair, Kuhn, & Kueffer, 2015) and poor species identifi
-cation (Thurn, Mercer, & Weisel, 2012), both blacklists and whitelists can be easily bypassed. Although in New Zealand all incoming travel
-lers, shipping containers and mail items are screened for potential risk goods, this is not the case in most other countries where national bor
-ders are more porous and the biosecurity infrastructure less effective.
As a consequence, legislation often has to be updated retrospectively
following the discovery that a previously introduced species has be
-come invasive in the territory. Under these circumstances, policy con
-siderations shift from prohibiting entry towards preventing the wider dissemination and spread of species already in cultivation.
POST-BORDER BANNING OF INVASIVE
species being dropped from legislation. For example, in relation to a ban on the sale of five aquatic ornamental plants in Great Britain in
2013, the Ornamental Aquatic Trade Association (OATA) ensured
three species worth over US $4 million in annual sales were not listed
and "campaigned long and hard to make the proposed prohibition list
as short as possible" (OATA 2013). While surveys often reveal that the ornamental nursery industry supports the existing sales bans (Coats, Stack, & Rumpho, 2011; Humair et al., 2014; Vanderhoeven et al.,
2011; Verbrugge, Leuven, van Valkenburg, & van den Born, 2014),
such assessments may underestimate the intense industry opposition
and lobbying prior to any sales ban being implemented. In the future, it would be valuable for surveys on industry attitudes to new regulations
to be undertaken before any agreement with the government has been
reached in order to better capture motivations and concerns of horti
-cultural professionals. In addition, if mechanisms to enforce regulations
are weak then compliance with legislation is often poor. An assessment
of over 1,000 ornamental nurseries in the United States indicated rates
of compliance with invasive species regulations to be <SO% (Oele, Wagner, Mikulyuk, Seeley-Schreck, & Hauxwell, 2015).
Sales bans can also be ineffective in limiting the negative impact of plant invasions if the target species is already widespread in the region. The consultation on banning plants from sale in Great Britain initially
targeted 15 species, however, several of these were already so wi
de-spread that the logic of any sales ban impacting on their future spread
was challenged by the ornamental industry and these species were
not listed (Figure 3). Even for the five species that were subsequently
banned from sale, the legislation will have greatest impact on the two
least common species: floating pennywort Hydrocotyle ranunculoides
and water primrose Ludwigia grandiflora. For the remaining three
spe-cies, a sales ban may be insufficient to prevent further spread and thus,
to be most effective, the legislation would need to be supported by a
coordinated eradication campaign. Even under this ideal scenario, es-capes will continue to occur through natural dispersal and illegal
dump-ing of green waste from existing plantings in public and private gardens.
CODES OF CONDUCT AND INDUSTRY
Increasing governmental support for deregulation combined with
industry opposition to restrictive legislation has led to a progressive
emphasis on corporate responsibility and voluntary codes of con
-duct world-wide (Sethi, 2011). Several voluntary codes of conduct
have been developed to address the management of invasive plant
species by the ornamental nursery industry (Baskin, 2002; Heywood & Brunei, 2009; Verbrugge et al., 2014). These voluntary codes of conduct suffer from a number of drawbacks that limit their contribu
-tion to preventing the import, propagation and sale of invasive plants.
An important aspect of any voluntary code of conduct is that there
should be consequences for non-compliance in terms of bad public
-ity and brand image. This requires that suppliers and customers can
readily identify actors participating in voluntary codes of conduct and
would involve procedures to audit compliance reasonably frequently.
~60 • Species subject to sales ban c: 0 Species not banned from sale ]
...~ 40 (!) E
"'Cl> Q. 30
"u u 0 20
su Cl> X 10 0
en)> Q f;
~II> Q. Q.
"'o- 'Q. ~
"'iil ~ cq
g.!g, 3 II>
gII> iil IS
FIGURE 3 Fifteen plant species proposed for a sales ban (Defra 2007) and the percentage of hectads (10 x 10 km grid cells) in which each occurs in Great Britain (data.nbn.org.uk). Species finally banned
from sale are highlighted in by black bars with the exception of
Ludwigia grandiflora which is present in < 1% of hectads
Therefore, while it is crucial to monitor and evaluate the performance
of codes of conduct, and to ensure public disclosure, these actions
have never been included in voluntary codes of conduct for the orna
-mental nursery industry. As there are no means of assessing how well
the codes work, there is seldom sufficient market incentive or social
leverage to adopt voluntary codes of conduct. As a result of these li
m-itations, the uptake of voluntary codes of conduct is generally poor
in the ornamental nursery industry (Burt et al., 2007; Hulme, 2015b).
In addition, voluntary codes of conduct need to be supported by
evidence-based and independent advice regarding which plant spe-cies currently on the global market are potentially invasive in a par
-ticular region, so as to prevent their import, distribution and sale. This
requires risk assessments of many hundreds of species. Who should
pay for this? While risk assessment costs might be funded through
an industry levy, the industry can be resistant to such additional costs
(Barbier et al., 2013). Furthermore, unless an importer has exclusive
rights to the sale and distribution of a plant taxon there is no incentive for them to invest in costly risk assessment when their competitors
would also benefit from the introduction without any financial outlay.
Consequently, whether the cost of weed risk assessment is borne
by industry (as in New Zealand) or by government (as in Australia), it has a major influence on the deliberate introduction of alien species
by industry. Since the late 1990s, New Zealand has approved fewer
than 100 plant species for cultivation (EPA 2017), while over the same
period more than 1,500 alien species have been permitted entry into
Australia (Riddle, Porritt, & Reading, 2008). While other models of funding exist, such as through NGOs (PiantRight 2017), the contrast
between New Zealand and Australia suggests that when the cost of
-0-uub;u=oublrou|bm]m;rѴ-m|vr;1b;v0|mo|_;m]o;uml;m|v -u;ru;r-u;7|o1o;u|_;;r;mv;ĺo;;uķ]o;uml;m|vrrou|bv Ѵbh;Ѵ|o0;bm1u;-vbm]Ѵ7;r;m7;m|om;b|_;u1olrѴvou-7_;u;m1;ou oѴm|-u1o7;vo=1om71||_-|-u;b7;Ѵvrrou|;7ķuo0v|-m7;u-b=b-0Ѵ;ĺ-m-1_-m];bm1omvl;u1_ob1;bm=Ѵ;m1;|_;bm7v|u|o0; lou;1olrѴb-m|ĵ
$)! "$( ҃("(
$""$_;l-foub|o=oum-l;m|-ѴrѴ-m|v-u;ru1_-v;70|_;];m;u-Ѵr0Ѵb1 Ő-um;ķ ƑƏƐƓőĺ o;uml;m|-Ѵ -m7 momŊ]o;uml;m|-Ѵ ou]-mb-|bomv -u;blrou|-m|ruo1u;uvo=oum-l;m|-ѴrѴ-m|v0||_;];m;u-ѴѴ-1-1om|=ou-u;Ѵ-|b;Ѵvl-ѴѴķ-m7o=|;mvr;1b-Ѵbv|Ő;ĺ]ĺm-|b;vr;1b;vő v_-u;o=|_;l-uh;|Ő b]u;Ƒőĺ$_vķ;71-|bm]|_;];m;u-Ѵr0Ѵb1|o l-h; bm=oul;7 1_ob1;v |o-u7v ru1_-vbm] m-|b; ou momŊbm-vb; rѴ-m| vr;1b;v bv o=|;m v;;m -v |_; l-bm l;1_-mbvl |_uo]_ _b1_ 1omvl;uv 1-m u;71; |_; ubvh o= -Ѵb;m rѴ-m| bm-vbomv Ő!;b1_-u7 ş )_b|;ķƑƏƏƐőĺomv;u-|bomv-u;bm1u;-vbm]Ѵouhbm]b|_|_; oum-l;m|-Ѵ muv;u bm7v|u |o u;lo; ro|;m|b-ѴѴ bm-vb; rѴ-m|v =uol v-Ѵ; -m7 ruolo|; m-|b; ou momŊbm-vb; -Ѵ|;um-|b;v |_uo]_ ruo]u-ll;v v1_ -v Ѵ-m|!b]_| bm |_; &mb|;7 "|-|;v -m7 ľuo ;mv|;-7ĴĿbmv|u-Ѵb-Ő u;;|-ѴĺķƑƏƐƏĸb;lb;u-ş(omoѴѴ;ķ ƑƏƏƖőĺ ;;u|_;Ѵ;vvķ l-m 1omvl;uv _-; - ru;=;u;m1; =ou -Ѵb;m rѴ-m|vr;1b;vo;um-|b;vŐuv;hş-uh;vvķƑƏƏƖĸ-|_ş;u;ķ ƑƏƐƐő l-hbm] 1_ob1;v 0-v;7 om =Ѵo;u vb;ķ 1oѴou -m7 =oѴb-]; -|-|ub0|;vŐ;m7-Ѵķ)bѴѴb-lvķş)bѴѴb-lvķƑƏƐƑĸ(;u0u]];;|-ѴĺķƑƏƐƓőĺ uolo|bm]momŊbm-vb;-Ѵb;mrѴ-m|v-v-Ѵ|;um-|b;v1-m-Ѵvo0;ruo0-Ѵ;l-|b1vbm1;|_;-||ub0|;v|_;r0Ѵb1Ѵooh=oubmoum-l;m|-ѴrѴ-m|v Ő;ĺ]ĺ1omvbv|;m|r;u=oul-m1;ķ];m;u-Ѵbv|]uobm]u;tbu;l;m|ķu;vbv|--m1;|or;v|vou7bv;-v;v-m7u;tbubm]Ѵb||Ѵ;l-bm|;m-m1;ő-u;|u-b|v |_-|1-m-Ѵvo=-1bѴb|-|;rѴ-m|bm-vbomvŐѴl;ķƑƏƐƐőĺomvl;uv-u; v;mvb|b; |o rub1;ķ -m7 ru;=;u;m1;v =ou m-|b; -m7 -Ѵb;m rѴ-m|v l- v_b=| _;u; 1ov| 7b==;u;m|b-Ѵv -u; v==b1b;m|Ѵ Ѵ-u]; Ő+;ķ uѴ;ķ ş m7;uvomķƑƏƐƐőĺo;;uķ7b==;u;m|b-Ѵrub1bm]oѴ7;b|_;uu;tbu; ]o;uml;m|v |o blrov; vol; =oul o= ;mbuoml;m|-Ѵ |- ou =ou |_; bm7v|u|o-]u;;|o1omvbv|;m|lbmbllrub1bm]o=ro|;m|b-ѴѴbm--vb;-Ѵb;mrѴ-m|vķm;b|_;uo=_b1_-rr;-uv-r-u|b1Ѵ-uѴb-0Ѵ;or|bom Ő-u0b;u;|-ѴĺķƑƏƐƒőĺ
oohѴ;|vruolo|bm]-Ѵ|;um-|b;vr;1b;vķrorѴ-ul-]-bm;-u|b1Ѵ;v _b]_Ѵb]_|bm] bm-vb; oum-l;m|-Ѵvķ =-1|v_;;|v 7;v1ub0bm] -rruorub--|; 7bvrov-Ѵ o= ]u;;m-v|;ķ -m7 ;;m ;m7ouv;l;m|v =uol 1;Ѵ;0ub| ]-u7;m;uv-ѴѴ_-;-uoѴ;|orѴ-bmu-bvbm]--u;m;vv-0o|bm-vb; oum-l;m|-Ѵ rѴ-m|v Ő-u1_-m|; ş -u1_-m|;ķ ƑƏƐѵőĺ o;;uķ 0;- _-bou-Ѵ1_-m];bvlou;Ѵbh;Ѵ_;u;|_;r0Ѵb1_-v_-m7vŊom;r;ub-;m1;bm|_;u;lo-Ѵo=bm-vb;-Ѵb;mvr;1b;v=uolm-|b;;1ovv|;lv Ő;u;mѴ;m7;uķ u-ѴѴķ ubѴѴķ uv0ķ ş -ѴѴ-u7ķ ƑƏƐѵőĺ = v1_ -1|bb|b;v 1oѴ70;vromvou;70Ѵo1-Ѵoum-l;m|-Ѵmuv;u0vbm;vv;v-m7lo-0bѴb;-oѴm|;;uouh=ou1;7u-m=uol]-u7;mbm]1Ѵ0vķ_ou|b1Ѵ|u-Ѵ vo1b;|b;v -m7 Ѵ-m7v1-r; ruo=;vvbom-Ѵvķ |_bv l- 0; |_; ]uom7v;ѴѴ m;;7;7|ov_b=|-||b|7;v-1uovv|_;vrrѴ1_-bmĺ
!$$"& $!$"ĵ$_;;-lbm-|bomo==oul-fouroѴb1bmv|ul;m|v|-u];|bm]|_;oum-l;m-|-Ѵbm7v|uvrrѴ1_-bm_b]_Ѵb]_|v|_-|_bѴ;;-1__-v|_;ro|;m|b-Ѵ|o 1om|ub0|;|ou;71bm]|_;ubvho=rѴ-m|bm-vbomvķmom;bvv==b1b;m|omb|v om|ov|;l|_;ruo0Ѵ;lĺo;;uķbm|;]u-|bm]|_;v;roѴb1bmv|ul;m|v -Ѵom]|_;oum-l;m|-Ѵbm7v|uvrrѴ1_-bmoѴ7ruo]u;vvb;Ѵu;71; |_;ubvhlou;;==;1|b;Ѵĺ oulov|1om|ub;vķ|_;u;-u;=;l;1_-mbvlv |ov1u;;mro|;m|b-ѴѴbm-vb;rѴ-m|vr;1b;v0;=ou;|_;;m|;u|_;oum-- l;m|-Ѵ|u-7;ĺ$_bv1oѴ70;=-1bѴb|-|;7b=|_;|u-1hbm]ķѴ-0;ѴѴbm]-m7lomb-|oubm]o=rѴ-m|blrou|v;u;0;||;u_-ulomb;7b|_m-|bom-Ѵu;]Ѵ-|bomv -77u;vvbm]rѴ-m|_;-Ѵ|_ĺ"1_-1|bb|b;voѴ7m;;7|o0;vrrou|;70 blr-u|b-Ѵ-m7bm7;r;m7;m|;;7ubvh-vv;vvl;m|Ő b]u;Ɠőĺ )_bѴ;;;7ubvh-vv;vvl;m|-blv|o7;|;ulbm;_;|_;u-vr;1b;v v_oѴ70;-11;r|;7ouu;f;1|;7=uolblrou|-m7ņouv-Ѵ;ķ-rruobl-|;Ѵ ƑƏѷo=vr;1b;vv1u;;m;71-mmo|v-ѴѴ0;1-|;]oub;7b|_1;u|-bm| Ő!b77Ѵ;;|-ѴĺķƑƏƏѶőĺѴ;-uruo|o1oѴvm;;7|o0;=oѴѴo;7|o7;-Ѵb|_ 11;r|;7ķ!;f;1|;7-m7&m1;u|-bmvr;1b;vŐ b]u;Ɠőĺ11;r|;7vr;1b;vķ _;|_;u-vv;vv;7ru;Ŋourov|Ŋ0ou7;uķv_oѴ70;-77;7|o-m-|bom-Ѵ_-b|;Ѵbv|-m7ķrom;m|;ubm]|_;l-uh;|ķѴ-0;ѴѴ;7-v_-bm]-ѴoѴbh;Ѵb_oo7 o=bm-vbomŐľu;;mĿѴ-0;ѴѴbm]őbmou7;u|ou;bm=ou1;r0Ѵb1orbmbomu;-]-u7bm]v1_ubvhvĺ||_;0ou7;uķm1;u|-bm-m7u;f;1|;7vr;1b;vv_oѴ7 0;ruo_b0b|;7=uol;m|uĺ oum1;u|-bmvr;1b;vķ7-|-]-rv|_-|lb]_| _;Ѵru;71;m1;u|-bm|v_oѴ70;b7;m|b=b;7-m71ollmb1-|;7|o|_; bm7v|uķ_bѴ;u;f;1|;7vr;1b;v-u;-77;7|o-m-rruorub-|;0Ѵ-1hѴbv| Ő b]u;Ɠ-őĺmbm1u;-vbm]ruorou|bomo=oum-l;m|-Ѵ|u-7;bmoѴ;vv-Ѵ;v o=1Ѵ|b-uv-m7-ub;|b;vķ;|-h;-u;-o=m1;u|-bm|bv_;|_;uv0-vr;1b;v-m7-ub;|b;vv_oѴ70;-vv;vv;7-||_;bm=u-vr;1b=b1ouvr;1b=b1 Ѵ;;Ѵĺ)_bѴ;;;7ubvh-vv;vvl;m|-rruo-1_;v-u;vb|-0Ѵ;=ouv1u;;mbm] vr;1b;v -| |_; bm=u-vr;1b=b1 Ѵ;;Ѵ |_-| -u; |u; |o |r; Őou7om ;|-Ѵĺķ ƑƏƐѵő|_;7omo|-11om|=ou|_;=-1||_-|momŊbm-vb;1Ѵ|b-uvl- u;;u|0-1h|obm-vb;=oulvŐu-m7ķ;_u;uķş0;ѴѴķƑƏƐƑőĺ
(a) Pre border policy integration
(b) Post-border policy Integration
ISpedes widespread Spedes localised
FIGURE 4 Schematic representation of how different policy
instruments can be integrated for different categories of plant species screened following weed risk assessment either (a) pre
-border or (b) post--border
While the important role of government, industry and the public in stemming the threat from invasive alien plants is well recognized, there has been little guidance to date as to how actions appropriate for each stakeholder could be better coordinated and more complementary. The foregoing scheme (Figure 4) proposes a clearer mechanism for i ntegra-tion but its delivery will require the development of closer partnerships between government, NGOs and industry, perhaps through a joint body that oversees the outcomes of independent weed risk assessment, ad-vances the effectiveness of codes of conduct, informs priorities for sales bans, endorses appropriate labelling and promotes consumer education.
Closing the plant invasion pathway associated with ornamental horticul-ture requires government-industry agreements to fund effective pre-and post-border weed risk assessments that can be subsequently supported by widely adopted, as well as verifiable, industry codes of conduct This will ensure that producers and consumers make informed choices in the face of better targeted public education addressing plant invasions.
Research was supported by COST Action TD1209 "Alien Challenge". The authors are grateful to John David and Franziska Humair for valu-able discussions on this topic. P.P. and J.P. were supported by project no.
14-36079G Centre of Excellence PLADIAS (Czech Science Foundation) and RVO 67985939 (The Czech Academy of Sciences). F.E., S.D., M.C. and M.v.K. were supported by the ERA-Net BiodivERsA through the Austrian Science Fund, German Research Foundation and French National Research Agency. AN. was supported by the Working for Water fM/fW) Programme and the DST-NRF Centre of Excellence for Invasion Biology. H.S. acknowledges support by the DFG (grant SE 1891/2-1).
P.E.H. conceived the ideas and led the writing of the manuscript. All authors contributed critically to the drafts and gave final approval for publication.
Data have not been archived because all data presented are in the public domain. See Barney (2014), Harris et al. (2009), Weber (2003).
More detail available in Figure legends.
Agriculture-Canada (2015). Statistical overview of the Canadian ornamental industry. Ottowa: Canada Government.
Armitage, J., Edwards, D., Konyves, K., Lancaster, N., Marshall, R., Cubey, J., & Merrick, J. (2016). RHS plant finder 2016. Wisley: Royal Horticultural Society.
Auld, B. (2012). An overview of pre-border weed risk assessment and post-border weed risk management protocols. Plant Protection Quarterly, 2 7, 105-111.
Barbier, E. B., Knowler, D., Gwatipedza, J., Reichard, S. H., & Hodges, A. R. (2013). Implementing policies to control invasive plant species. BioScience, 63, 132-138.
Barney, D. (2014). Horticultural supply in the UK- A supply-chain map. Louth:
Horticulture Innovation Partnership.
Baskin, Y. (2002). The greening of horticulture: New codes of conduct aim to curb plant invasions. BioScience, 52, 464-471.
Brand, M. H., Lehrer, J. M., & Lubell, J. D. (2012). Fecundity of Japanese barberry (Berberis thunbergii) cultivars and their ability to invade a de-ciduous woodland.lnvasive Plant Science and Management, 5, 464-476. Brzuszek, R. F., & Harkess, R. L. (2009). Green industry survey of native plant marketing in the southeastern United States. Horttechnology, 19, 168-172. Burt, J. W., Muir, A. A., Piovia-Scott, J., Veblen, K. E., Chang, A. L., Grossman, J. D., & Weiskel, H. W. (2007). Preventing horticultural introductions of invasive plants: Potential efficacy of voluntary initiatives. Biological Invasions, 9, 909-923.
Coats, V. C., Stack, L. B., & Rumpho, M. E. (2011). Maine nursery and land-scape industry perspectives on invasive plant issues. Invasive Plant
Science and Management, 4, 378-389.
Defra (2007). Consultation on the ban on sale of certain non-native species. London: Department for Environment, Food and Rural Affairs. Defra (2016). Agriculture in the United Kingdom. London: Department for
Environment, Food and Rural Affairs.
o77ķĺĺķu]l-mķĺĺķ1-u|_ķĺĺķşbmvou|_ķĺŐƑƏƐƔőĺ$_; 1_-m]bm] r-||;umv o= rѴ-m| m-|u-Ѵb-|bom bm v|u-Ѵb-ĺ Diversity and
u;ķĺķm7;uvomķĺķşm7oķ ĺŐƑƏƐƏőĺomm7ulvo=-1olrѴ;;1- |ou=oubm-vb;vr;1b;v1om|uoѴĹ7;|-bѴ;7;-lbm-|bomo=|_;_ou|b1Ѵ-|u-Ѵbm7v|uĺBiological Invasionsķ12ķƑѶƒƕŋƑѶƔƐĺ
ŐƑƏƐƕőĺ New plants in New Zealandĺ );ѴѴbm]|omĹ mbuoml;m|-Ѵ uo|;1|bom|_oub|ĺ!;|ub;;7=uol_||rĹņņĺ;r-ĺ]o|ĺm vvѴķ ĺķ ;_ubm]ķ "ĺķ Ѵbm];mv|;bmķ ĺķ bѴ-vovhķ ĺķ o-1hķ ĺķ ş
!-0b|v1_ķ )ĺ ŐƑƏƐƐőĺ !;b; o= ubvh -vv;vvl;m| vv|;lv o= " bm uor; -m7 bm|uo71bm] |_; ;ul-mŊv|ub-m Ѵ-1h bv| m=oul-|bom "v|;lŐ"őĺJournal for Nature Conservationķ19ķƒƒƖŋƒƔƏĺ -Ѵhm;uķ ĺ $ĺķ !o0;u|vomķ ĺ ĺķ !o];|ķ ĺķ ş )bѴvomķ ĺ !ĺ &ĺ ŐƑƏƐѵőĺ
&m7;uv|-m7bm]-m7l-m-]bm]|_;bm|uo71|bomr-|_-vo=-Ѵb;m|--Ĺ "o|_=ub1--v-1-v;v|7ĺBiological Invasionsķ18ķƕƒŋѶƕĺ
-77lķ ĺ ŐƐƖƖƖőĺ Gaddum’s plant finder 2000ĺ bv0oum;ķ ,Ĺ ; ,;-Ѵ-m7Ѵ-m| bm7;uĺ
ou7omķ ĺ !ĺķ Ѵouķ "ĺ ĺķ b;u-m1;ķ ĺķ Ѵl;ķ ĺ ĺķ 77;m_-];mķ ĺķ -|omķĺķĻ(bѴ-ķĺŐƑƏƐѵőĺ);;7ubvh-vv;vvl;m|v-u;-m;==;1|b; 1olrom;m| o= bm-vbom ubvh l-m-];l;m|ĺ Invasive Plant Science and
-uubvķĺķb-m]ķĺķbķ ĺĺķub-mķ,ĺķş;ķĺ$ĺŐƑƏƏƖőĺ$;v|bm]|_;uoѴ;v o=vr;1b;vm-|b;oub]bm-m7=-lbѴl;l0;uv_brbmbm|;m|bom-ѴrѴ-m|bm-|uo71|bomvvbm]muv;u7-|--1uovv|_;v|-|;o=;m|1hĺJournal of
the Torrey Botanical Societyķ136ķƐƑƑŋƐƑƕĺ
;oo7ķ(ĺķşum;Ѵķ"ĺŐƑƏƏƖőĺCode of conduct on horticulture and
inva-sive alien speciesĺ"|u-v0ou]Ĺom1bѴo=uor;ĺ
Ѵl;ķĺĺŐƑƏƐƐőĺ77u;vvbm]|_;|_u;-||o0bo7b;uvb|=uol0o|-mb1]-u-7;mvĺTrends in Ecology & Evolutionķ26ķƐѵѶŋƐƕƓĺ
Ѵl;ķĺĺŐƑƏƐƑőĺ);;7ubvh-vv;vvl;m|Ĺ-=ou-u7ou--v|;o= |bl;ĵJournal of Applied Ecologyķ49ķƐƏŋƐƖĺ
Ѵl;ķĺĺŐƑƏƐƔ-őĺm-vbomr-|_-v-|-1uovvuo-7ĹoѴb1-m7u;v;-u1_ 1_-ѴѴ;m];v=oul-m-]bm]-Ѵb;mvr;1b;vbm|uo71|bomvĺJournal of Applied Ecologyķ52ķƐƓƐѶŋƐƓƑƓĺ Ѵl;ķĺĺŐƑƏƐƔ0őĺ!;voѴbm]_;|_;u0o|-mb1]-u7;mv-u;om|_;uo-7 |o1omv;u-|bomou-r-|_-=ourѴ-m|bm-vbomvĺConservation Biologyķ 29ķѶƐѵŋѶƑƓĺ l-buķ ĺķl-buķĺķ_mķ ĺķş;==;uķĺŐƑƏƐƔőĺŊ1oll;u1;|u-7;bm bm-vb;rѴ-m|vĺConservation Biologyķ29ķƐѵƔѶŋƐѵѵƔĺ
l-buķ ĺķ ;==;uķ ĺķ ş "b;]ubv|ķ ĺ ŐƑƏƐƓőĺu; momŊm-|b; rѴ-m|v r;u- 1;b;7|o0;lou;ubvhĵ -1|ouvbm=Ѵ;m1bm]_ou|b1Ѵ|ubv|vĽubvhr;u1;r-|bomvo=oum-l;m|-ѴrѴ-m|vr;1b;vĺPLoS ONEķ9ķ;ƐƏƑƐƑƐĺ
b-m]ķĺķ -mķ ĺķbķĺ$ĺķ"_bķ"ĺķbķ"ĺĺķb-oķ)ĺĺķş"_ķ)ĺ"ĺŐƑƏƐƐőĺ -|u-Ѵb-|bomo=-Ѵb;mrѴ-m|vbm_bm-ĺBiodiversity and Conservationķ20ķ 1545–1556.
-blķ ĺķ ş ;ѴѴ;uķ "ĺ ŐƑƏƏƖőĺ m-Ѵvbv o= vrrѴŊ1_-bm l-m-];l;m|Ĺ -v;v|7b;vo=|_;l-uh;|=oumuv;uruo71|vbm;ul-mĺmĺĺ rr;m_;blŐ7ĺőķXVI International symposium on horticultural economics
-|_ķĺĺķş;u;ķĺĺŐƑƏƐƐőĺm7v|uvu;o=|_;m-|b;bѴ7=Ѵo;u l-uh;|bm Ѵoub7-ĺHorttechnologyķ21ķƕƕƖŋƕѶѶĺ
;ѴѴ;uķ!ĺĺķo7];ķ ĺĺķş bmmo==ķ ĺĺŐƑƏƏƕőĺ!bvh-vv;vvl;m|=oubm--vb;vr;1b;vruo71;vm;|0bo;1omolb10;m;=b|vĺProceedings of the
National Academy of Sciencesķ104ķƑƏƒŋƑƏƕĺ
;m7-Ѵķ ĺķ )bѴѴb-lvķ ĺ ĺ ĺķ ş )bѴѴb-lvķ ĺ "ĺ ĺ ŐƑƏƐƑőĺ Ѵ-m| |u-b|v Ѵbmh r;orѴ;Ľv rѴ-m| ru;=;u;m1;v |o |_; 1olrovb|bom o= |_;bu ]-u7;mvĺ
Landscape and Urban Planningķ105ķƒƓŋƓƑĺ
-l07omķĺ)ĺķv;hķĺķ-vmoķĺķ;f7-ķĺķub-mo|voķĺķvvѴķ ĺķ ĻѴl;ķĺĺŐƑƏƏѶőĺѴb;m=Ѵou-o=uor;Ĺ"r;1b;v7b;uvb|ķ|;lrou-Ѵ |u;m7vķ];o]u-r_b1-Ѵr-||;umv-m7u;v;-u1_m;;7vĺPresliaķ80ķƐƏƐŋƐƓƖĺ
;_-mķĺĺķur_ķĺ!ĺķ$_ou0umķĺĺķşu-7Ѵ;ķĺĺŐƑƏƐƒőĺ11b7;m|-Ѵ bm|uo71|bomv-u;-mblrou|-m|vou1;o=bm-vb;rѴ-m|vbm|_;1om|b-m;m|-Ѵ&mb|;7"|-|;vĺAmerican Journal of Botanyķ100ķƐƑѶƕŋƐƑƖƒĺ -u1_-m|;ķĺķş-u1_-m|;ķĺŐƑƏƐѵőĺm]-]bm]vo1b;||o=b]_|bm-vb;
-Ѵb;mrѴ-m|vbmou|]-ѴŌm;o=|_;l-bm|_u;-|v|o0bo7b;uvb|ĺmĺ -v|uoķ&ĺĺ;b|;buoķĺ-1;Ѵ-uŊb1oѴ-ķ)ĺ;-Ѵ bѴ_oşĺĺѴ Ő7vĺőķBiodiversity and education for sustainable developmentŐrrĺƐƏƕŋ ƐƑƑőĺ_-lĹ"rubm];uĺ ;u;mѴ;m7;uķĺĺķu-ѴѴķĺ)ĺķ ubѴѴķ"ĺķuv0ķĺķş-ѴѴ-u7ķĺŐƑƏƐѵőĺ -Ѵ-|bm];mbuoml;m|-Ѵ;71-|bomķ1b|b;mv1b;m1;ķ-m7v|;-u7v_br |_uo]_m-|u-Ѵbv|ruo]u-lvĺConservation Biologyķ30ķƐƑƔƔŋƐƑѵƔĺ b;lb;u-ķĺ*ĺķş(omoѴѴ;ķĺŐƑƏƏƖőĺm-vb;rѴ-m|vr;1b;v-m7|_;ou-m-l;m|-Ѵ_ou|b1Ѵ|u;bm7v|uĺmm7;ufb|Ő7ĺőķManagement of invasive weedsŐrrĺƐѵƕŋƐѶƕőĺ;+ouhķ+Ĺ"rubm];uĺ
$ŐƑƏƐƒőĺAnnual review 2012/13ĺ);v|0uĹum-l;m|-Ѵt-|b1$u-7;ĺ ;Ѵ;ķ ĺĺķ)-]m;uķĺĺķbhѴhķĺķ";;Ѵ;Ŋ"1_u;1hķĺķş-;ѴѴķĺĺ
ŐƑƏƐƔőĺ==;1|bm]1olrѴb-m1;b|_bm-vb;vr;1b;vu;]Ѵ-|bomv|_uo]_ o|u;-1_-m7;71-|bomo=Ѵb;rѴ-m|u;|-bѴ;uvĺBiological Invasionsķ17ķ 2707–2716.
ŐƑƏƐƔőĺProduction nurseriesĺ-m0;uu-ķ$ĹѴ-m|;-Ѵ|_v|u-Ѵb-ĺ Ѵ-m|!b]_|ŐƑƏƐƕőĺPlantRight: Promoting noninvasive plants for Californiaĺ"-m
!b77Ѵ;ķĺķouub||ķ ĺķş!;-7bm]ķĺĺŐƑƏƏѶőĺv|u-Ѵb-Ľv;;7ubvh-vv;vv-l;m|vv|;l-m7|_;r;ulb||;7v;;7vѴbv|ĺPlant Protection Quarterlyķ
";|_bķ"ĺĺŐƑƏƐƐőĺ";Ѵ=Ŋu;]Ѵ-|bom|_uo]_oѴm|-u1o7;vo=1om71|ĺm"ĺĺ ";|_bŐ7ĺőķGlobalization and self-regulation: The crucial role that corporate
codes of conduct play in global businessŐrrĺƒŋƐѵőĺ;+ouhĹ-Ѵ]u-;ĺ
$_lķ!ĺĺķ;u1;uķĺ$ĺķş)1bv;Ѵķ ĺĺŐƑƏƐƑőĺoor_oѴ;vbm|_;u;]Ѵ--|bomo=bm-vb;vr;1b;vĹ;m;|b1b7;m|b=b1-|bomvb7;m|b=lbvѴ-0;Ѵbm]o= ruo_b0b|;7-t-ublrѴ-m|vĺBiological Invasionsķ14ķƖƑƖŋƖƒƕĺ &" ŐƑƏƐƓőĺCensus of agricultureĺ)-v_bm]|omĹ&" -|bom-Ѵ]ub1Ѵ|u-Ѵ "|-|bv|b1v";ub1;ĺ (-m7;u_o;;mķ"ĺķbt;u-ķĺķ-Ѵ=ou7ķĺķѴ;mvķĺķ(bm1h;ķĺķş-_ķ ĺŐƑƏƐƐőĺ;u1;r|bom-m7m7;uv|-m7bm]o=bm-vb;-Ѵb;mvr;1b;vbv-v;v0m-|u;1omv;u-|bom-m7_ou|b1Ѵ|u;ruo=;vvbom-Ѵvbm;Ѵ]blĺ Environmental Managementķ47ķƓƑƔŋƓƓƑĺ (;u0u]];ķĺĺĺķ;;mķ!ĺ"ĺĺ)ĺķ-m(-Ѵh;m0u]ķĺĺĺĺķş-m 7;m oumķ !ĺ ĺ ĺ ŐƑƏƐƓőĺ -Ѵ-|bm] v|-h;_oѴ7;u --u;m;vv -m7 bm- oѴ;l;m|bmubvhru;;m|bomo=-t-|b1bm-vb;rѴ-m|vr;1b;v0-m--|bom-Ѵ1o7;o=1om71|ĺAquatic Invasionsķ9ķƒѵƖŋƒѶƐĺ
);0;uķĺŐƑƏƏƒőĺInvasive plant species of the world: A reference guide to