Late Lessons, Jensen Huang and AI
Markdown version

LL2-20 hindsight check: Invasive alien species: a growing but neglected threat?#

Late lessons from early warnings: science, precaution, innovation (EEA Report No 1/2013), Chapter 20 (Sarah Brunel, Eladio Fernández-Galiano, Piero Genovesi, Vernon H. Heywood, Christoph Kueffer and David M. Richardson), report pp. 486–508 (PDF pp. 488–510). The chapter has no panels. Hindsight check carried out on 25–26 September 2026.

Method note. The web search tool’s session budget was used up before this check began. All evidence therefore comes from direct fetches of primary sources and bibliographic databases: - the EU Publications Office (the full texts of the IAS Regulation, the 2013 proposal, the Union list and its amendments, the Commission’s 2021 review, the Plant Health Regulation and CJEU records); - the IPBES assessment on Zenodo; - the IPPC/FAO text of ISPM 36; - the US Federal Register; - GOV.UK; - Europe PMC, Crossref and Semantic Scholar, for peer-reviewed papers and abstracts.

Four gaps remain: - Council of Europe (Bern Convention) site. It blocked automated access. The latest ruddy duck status is therefore taken from a March 2026 peer-reviewed paper that cites the Bern Convention’s 2023 progress report. - Elsevier. It blocked the Pimentel papers. Their attribution rests on how the InvaCost authors cite them and on the papers’ published titles and scope (flagged where used). - European Court of Auditors. I found no report of its own on invasive species, so none is cited. - Some papers. Only titles, not abstracts, were available for a few items; these are marked “title only”.

The chapter was new in 2013. The 2001 volume had no invasive species case, so Annex 3 of the 2013 report holds no update for it.

Insider note. Several of the later syntheses that confirm the chapter involve its own authors: - Genovesi co-authored Seebens et al. 2017 and 2021. - Richardson co-authored Seebens et al. 2025. - Genovesi and Richardson were review editors of the 2023 IPBES assessment. - Heywood’s code of conduct is showcased in the IPBES summary for policymakers. - Genovesi co-authored D’Andrea et al. 2025.

So agreement between the chapter and the later “consensus” is partly agreement of the field with itself. It is not independent confirmation. Where possible I have looked for sources outside that circle.

Overview#

The chapter (drafted 2011–12) makes three kinds of claim: 1. A diagnosis. Invasions are growing without saturation. They are costly, and prevention and rapid response are the most cost-effective remedies. 2. Institutional forecasts. An EU instrument would arrive by end-2012. The ruddy duck would be eradicated from Europe by 2015. Grey squirrels would spread across Europe. 3. Governance judgements. Voluntary codes underperform. Formally risk-assessed biocontrol is safe. Pathway regulation beats species-by-species inspection. New pathways loom (biofuel crops, synthetic biology, assisted migration).

Hindsight divides these sharply.

Claim 1: Invasions “continue to grow at a rapid rate, with no indication yet of any saturation effect” despite growing legislation (pp. 486, 493)#

Original claim. “Despite the growing amount of legislation being adopted at the global scale, biological invasions continue to grow at a rapid rate, with no indication yet of any saturation effect” (p. 486; repeated on p. 493, citing Butchart et al. 2010).

What happened next. - The first global test confirmed the claim. Seebens et al. (15 February 2017) analysed 45,813 first records of 16,926 established alien species. - The annual rate of first records rose over 200 years, with 37% of all first records made in 1970–2014. - “For all taxonomic groups, the increase in numbers of alien species does not show any sign of saturation and most taxa even show increases in the rate of first records over time … past efforts to mitigate invasions have not been effective enough to keep up with increasing globalization.” - Genovesi was a co-author. - New source pools keep opening. A quarter of first records in 2000–2005 were of species never before recorded as alien anywhere (Seebens et al. 2018). This supports the chapter’s “invaders in disguise” worry (p. 486) and its point that past invasiveness is an imperfect predictor (p. 490). - Projections. Established alien species per continent were projected to rise 36% between 2005 and 2050. The largest absolute rise is for Europe (+2,543 ± 237 species). Only Australasia shows declining (still positive) rates (Seebens et al. 2020/21). - The IPBES assessment (4 September 2023) agreed. More than 37,000 established alien species, about 200 new records a year, and a rate “predicted to rise even higher”. The number of alien species “has been rising continuously for centuries in all regions”. By 2050 the total is expected to be about a third higher than in 2005 under business as usual, and probably more (SPM KM-B2, A-section). - The latest global review (Seebens et al., August 2025, with Richardson as co-author): “The numbers of alien species are increasing within all taxa and across all regions, and are often even accelerating.” - Great Britain. The 2023 GB invasive non-native species strategy puts new establishments at 10–12 species a year. It sets a target to cut them by at least 50% against 2000 levels (GOV.UK, 27 February 2023). - Evidence that complicates the claim. - Seebens et al. (2017) itself found first-record rates for mammals and fishes “declined in recent decades”, after peaking around 1950. - Tedeschi et al. (2022) found first records of alien mammals in Europe falling since the 1960s, with “almost no first records” of the studied species in the last decade. They attributed this possibly to stricter rules on fur, game and pet species, “especially since” the EU Regulation, while noting it is “unclear” whether saturation or regulation explains it. - Bonnamour et al. (2021) found insect and plant invasion rates “did not continuously increase” but tracked two waves of globalisation. That challenges the idea of steady acceleration.

Verdict: held up. The core empirical claim of no saturation was tested directly after publication and confirmed at global scale. Later assessments reinforced it. The one refinement: for deliberately traded vertebrates, first-record rates have fallen, which hints that controls on intentional introductions can work.

Implications for weight. This is the chapter’s most robust claim. The general pattern carries full weight: introductions scale with the volume and reach of trade, and case-by-case legislation has not bent the curve. The nuance also matters. Controls work best where the pathway is deliberate and the traded items are identifiable. They work least well for contaminants and stowaways (pp. 498–499), which feeds directly into claim 10.

Claim 2: A dedicated EU instrument by end-2012, “likely … before 2013, to be implemented in the following years” (pp. 492, 493, 501)#

Original claim. “The European Commission is preparing a dedicated legislative instrument to be ready by the end of 2012” (Box 20.1, p. 492). “The EU has committed to presenting a draft dedicated legal tool by the end of 2012” (p. 493). Box 20.4 (p. 501) says one is “likely … before 2013, to be implemented in the following years, but 2013 is twenty years after scientists alerted governments”. The chapter also argued: - governments’ claim that EU free movement barred national action was “a doubtful claim” (Box 20.4); - national efforts would have “limited effectiveness until there is a legal tool that can be applied across the EU” (p. 492).

What happened next. - Timing. - The Commission proposal, COM(2013) 620, was dated 9 September 2013, about nine months after the promised date. - Regulation (EU) No 1143/2014 was adopted on 22 October 2014 and entered into force on 1 January 2015 (Art. 33). - The first “Union list” took effect on 3 August 2016 (Implementing Regulation 2016/1141, 37 species). - Pathway action plans were due within three years of listing (Art. 13). - Measured from the chapter’s “around 1993”, enforceable EU-wide restrictions arrived after about 23 years. - Content: a black list, not a white list. - The Regulation restricts only listed “invasive alien species of Union concern”: no import, keeping, breeding, transport, sale, use, growing or release (Art. 7). - Listing requires a risk assessment and evidence that the species is alien to the Union, can establish in a biogeographic region shared by more than two Member States, has significant impact, and that listing will be effective (Art. 4(3)). - Recital 15 asks that listing be prioritised towards species not yet present or at an early stage of invasion. - The 2013 proposal capped the list at “a maximum of fifty species” (proposal Art. 4(4)). The cap was dropped in the adopted text. - The list was updated in 2017, 2019, 2022 and 2025 (Implementing Regulation 2025/1422 of 17 July 2025). The Commission reports 114 species (65 animals, 49 plants). - Species named in the chapter that are now listed: - listed in 2016: the grey squirrel, the ruddy duck, water hyacinth, signal crayfish, Ludwigia; - added only in 2025: the Asian knotweeds (Reynoutria japonica, R. sachalinensis, R. × bohemica). - The single market. The Regulation handles it the way the chapter wanted. - Uniform EU-wide bans aim to “avoid distortions of the internal market” and to stop “action taken in one Member State [being] undermined by inaction in another” (recital 18 of the Regulation; also the proposal’s problem analysis). - Member States may keep their own national lists and apply equivalent measures, provided these are “compatible with the TFEU and notified” (Art. 12). This vindicates Box 20.4’s view that free movement was not a real bar. - The Regulation is a prioritised list, not a reverse-onus “safe list”. The idea of safe lists has been developed since (Kumschick et al. 2024) but not adopted at EU level. - Effect: the Commission’s first review (COM(2021) 628, 13 October 2021). - The Regulation has “created a coherent framework”, and restrictions (e.g. “removal of species from trade”), rapid eradication and management “deliver benefits”. But it was “premature to draw conclusions on most aspects”. - Early detection (July 2016–March 2021): 135 notifications; rapid eradication was confirmed in 57 cases and judged not achieved in 30. - Management measures on widespread species (2016–2018): 6% achieved eradication, 21% reduced populations, 17% saw populations increase anyway, and 42% had unclear results. - Pathway action plans: only 10 of 22 Member States had submitted them by March 2021, and in June 2021 the Commission opened procedures against 18 Member States. - Listing is slow: at least two years for a risk assessment, then at least another year to decide. The list “by its nature … cannot include all IAS”. - The emergency and regional-cooperation provisions had never been used. - Two Member States were authorised to continue raccoon dog fur farming (Art. 9). - Member States reported compliance costs of about EUR 75 million over 2015–2018, which most consider an underestimate. - Enforcement. - The Court of Justice found that Bulgaria had failed to adopt pathway action plans and a surveillance system (Case C‑165/23, 14 November 2024). - An infringement case against Ireland over penalty provisions (C‑205/24) was closed by court order on 6 June 2025. I could not read the order. - Member States’ second reports were due in 2025. No second Commission review appears in EU Publications Office records to date (September 2026). - Outside view. Kurtul et al. (2024) still describe the EU effort as hampered by weak information exchange and differences between Member States. They argue for a central coordinating authority.

Verdict: partly held up. - The instrument arrived, and its design matched the chapter’s prescriptions: EU-wide trade bans, rapid eradication duties, pathway plans, and national lists allowed. - The timing forecast was optimistic, and “implemented in the following years” proved slow and uneven. - There is still no systematic evidence that the Regulation has reduced invasions or damage.

Implications for weight. The chapter’s late lesson (“do not take the need for European coordination as an excuse for inaction”, Box 20.4) is strengthened by what followed: the coordinated instrument took longer still, and implementation then lagged at Member State level. Several technology-neutral mechanisms are well evidenced here: - The list lag. A risk-assessed list is scientifically defensible but slow, taking three years or more per species. - The prioritised list excludes by design, so harmful but unlisted items stay legal. Japanese knotweed was listed only in 2025. - A higher-level mandate does not produce national delivery without enforcement.

Claim 3: Invasive species cost Europe more than EUR 12.5 billion a year against EUR 40–190 million for action (“a very cost-effective investment”); global costs of up to USD 1.4 trillion a year, about 5% of global GDP (Pimentel et al. 2005) (pp. 491, 494)#

Original claim. “The economic costs of invasive alien species in the region exceed EUR 12.5 billion/year (Kettunen et al., 2009)” (p. 491). “The cost of inaction has been estimated at up to USD 1.4 trillion per year, representing about 5 % of global GDP (Pimentel et al., 2005) … While the cost of inaction in Europe is EUR 12 billion per year, the cost of action is estimated at EUR 40–190 million per year … The management of IAS is therefore, according to this perspective, considered a very cost-effective investment” (p. 494). On p. 488, the chapter calls Pimentel et al.’s count of 50,000 alien species in the US “misleading unless broken down”.

What happened next. - The European figure was conservative. - The Commission’s 2013 proposal used “at least € 12 billion per year”. - InvaCost analysis (Haubrock et al., 29 July 2021): recorded European costs of USD 140.2 billion (EUR 116.6 billion) over 1960–2020. Costs “increased exponentially”, reaching up to EUR 19.64 billion in 2013, with a model extrapolation of EUR 116 billion in 2020. The 2020 figure is an extrapolation and much less secure than the recorded series. - Henry et al. (8 June 2023): only about 1% (259 of 13,331) of IAS in the EU have any reported cost. Filling the gaps raised the estimate of observed costs by about 500%, and costs were projected to rise substantially by 2040. - Both groups stress that European costs are “severely underestimated”. - The global USD 1.4 trillion figure was misattributed and has been superseded. - Pimentel, Zuniga and Morrison (2005) is a US-only update (about USD 120 billion a year). The global 1.4 trillion/5% extrapolation comes from Pimentel et al. (2001), which scaled up from six countries. Both points rest on the papers’ titles and published abstracts, which could not be re-opened for this check (publisher blocked); treat them as not re-verified. The InvaCost authors cite Pimentel et al. 2001 and Pimentel 2011 as “the only available global estimates” and call them “outdated and suffer from methodological flaws that were already highlighted” (Diagne et al. 2020, Scientific Data). - The chapter criticises Pimentel’s species count as “misleading” (p. 488) but uses the Pimentel-group global cost uncritically (p. 494). - Later global estimates on documented costs: - Diagne et al. (31 March 2021): at least USD 1.288 trillion in total over 1970–2017, a mean of USD 26.8 billion a year, rising to an estimated USD 162.7 billion in 2017, with costs tripling each decade. - IPBES (2023): above USD 423 billion in 2019, “likely to be a gross underestimate”; 92% damage and 8% management. - The global figure could rise sharply again. A 2025 preprint using machine-learning extrapolation to 1,419 species in 184 countries puts total costs at USD 10.3 trillion over 1970–2020, “almost six times higher than previous estimates” (Caetano et al., March 2025; not peer-reviewed as far as I could find). - None of these later estimates reaches 5% of world GDP a year. The chapter’s global headline number is not supported by later work, though its direction (large and rising) is. - Cost-effectiveness logic: supported, but the chapter’s comparison was loose. - Cuthbert et al. (2022) found reported global management spending (USD 95.3 billion since 1960) to be 12 times less than damage costs. Pre-invasion spending was over 25 times lower than post-invasion spending. Management lagged damage reporting by about 11 years on average. They estimated the extra cost of those delays at about USD 1.2 trillion. - IPBES: eradication programmes are “generally cheaper than long-term and permanent control cost and impacts” (well established). - However, setting total existing damage (EUR 12 billion) against the cost of a new policy (EUR 40–190 million) does not show that the policy would avert that damage. Much of it comes from species that are already widespread and cannot be eradicated. - The Commission’s 2021 review said benefits are hard to monetise and “it is premature to evaluate the overall impact” of the Regulation. - Political effect. The chapter suggested that monetised costs had helped move EU institutions (p. 491; Box 20.4). The Commission’s proposal and review both lead with the EUR 12 billion figure, which is consistent with that suggestion.

Verdict: partly held up. - The European order of magnitude held up and was probably an underestimate. - The claim that costs are rising was strengthened. - The claim that prevention is cost-effective is supported in direction. - The global USD 1.4 trillion/5% figure was misattributed, rests on a criticised extrapolation, and is not supported by later work. - The damage-versus-action-cost comparison was rhetorically strong but analytically loose.

Implications for weight. - Treat the cost numbers as advocacy-grade: right direction, uncertain magnitude. - The general lesson (spending on prevention is small relative to damage, and management lags damage by about a decade) is now well evidenced (Cuthbert et al. 2022). - One more pattern is worth noting. Monetised totals travel into policy documents faster than their caveats do, and an advocacy chapter can be rigorous about an opponent-style number (species counts) while being uncritical about a helpful one (cost totals).

Claim 4: Prevention or very early eradication is most cost-effective; weed eradication costs rise at least 40-fold with delay and eradication “quickly becomes unfeasible”; Caulerpa taxifolia was a missed opportunity in France (1984) but eradicated in California (2000) (pp. 487, 498)#

Original claim. “The cost of eradicating weeds can increase at least 40 times if action is not taken promptly (Harris and Timmins, 2009), and in most cases eradication quickly becomes unfeasible” (p. 487). C. taxifolia “was detected in France in 1984 at a very early stage … management … only started when it had already expanded to a large portion of the Mediterranean … When the same species was recorded in California in 2000, eradication started only 17 days after its discovery, leading to its successful removal” (p. 498).

What happened next. - The mainstream position now matches the chapter. - IPBES (2023): “Preventing the introduction of invasive alien species is the most cost-effective management option” (C17, well established). - Early detection and rapid response “are effective at reducing rates of … establishment” (C18). - Eradication “has been successful and cost-effective … especially when their populations are small and slow-spreading”, with success in 88% of 1,550 island eradications. But “large-scale eradications are difficult and unlikely to be feasible in many cases”, and “there have been no fully successful eradication programmes for established invasive alien species in marine ecosystems” (C19). - EU law adopted the principle: recital 15 of the Regulation says “prevention is generally more environmentally desirable and cost-effective than reaction after the fact”; Art. 17 requires eradication within three months of early detection. - The cost-of-delay evidence was strengthened by modelling. - Ahmed et al. (2022): for Aedes mosquitoes, a 55-year delay added about USD 4.57 billion compared with acting seven years earlier. - Cuthbert et al. (2022): global management delays averaged 11 years and added about USD 1.2 trillion. - Ahmed et al. (2026), modelling five mammals in Japan: costs “begin to surge 40-80 years after the first record, with 90% of expected long-term damages incurred typically within 10-20 years”. - The specific “40 times” figure (Harris and Timmins 2009) comes from a single source. I found no later test of it. - A qualification on mechanism. Pluess et al. (2012), a global dataset of 136 eradication campaigns, found that “only the spatial extent of the infestation was significantly related to the eradication outcome”. Reaction time, knowledge and insularity “were all unrelated”. Speed matters because extent grows, not in itself. This is consistent with the chapter but shifts the emphasis from days to area. - Caulerpa in California. The 2000 incursion cost about USD 7 million to eradicate (Diaz et al. 2012). The eradication stands as a rare marine success, consistent with IPBES’s point that marine successes come only when detection is early. - Caulerpa in the Mediterranean. The later record complicates the “missed opportunity” story. On the Italian Ligurian coast, C. taxifolia “had an impressive expansion phase from 1984 to 2000 but then … did not persist in areas formerly colonized. Today, abundance … is strongly declined as it disappeared from most of the attained areas”. Meanwhile C. cylindracea kept expanding (Montefalcone et al. 2015). Balearic studies also describe C. taxifolia in regression (Tejada et al. 2013). - The damage was therefore less durable than the chapter’s framing implies. Boom-bust dynamics are a known pattern, though often overstated and “offered as a reason not to manage troublesome invaders” (Strayer et al. 2017). - The underlying lesson is being tested again. In June 2025 a related invader, C. taxifolia var. distichophylla, was found as more than 100 small colonies along about 600 m of coast in the Bay of Villefranche (Alpes-Maritimes). That is more than 500 km from the nearest known record (Meinesz et al., July 2026). I found no public record of whether an eradication attempt followed.

Verdict: held up. The central claim (prevention and very early action are most cost-effective, and feasibility falls with spread) is now the well-established consensus and has been strengthened by cost-of-delay modelling. Two caveats: - the 40-fold figure is a single-source number; - the French Caulerpa case, used as a counterfactual, looks less clear-cut given the alga’s later collapse.

Implications for weight. One of the chapter’s best-supported transferable insights: windows for intervention close as a hazard spreads, so precaution can mean acting fast, not only restricting in advance. The Caulerpa history adds a caution the chapter omits. Hindsight judgements of a “missed opportunity” assume the harm would persist. Some hazards peak and recede for reasons nobody predicted, which weakens retrospective blame but not the case for early action under uncertainty.

Claim 5: UK ruddy duck numbers were down to “a few hundred” by December 2011, with “good chances of eradicating the species from the wild in Europe by 2015” (p. 495)#

Original claim. “By December 2011 the number of birds in the United Kingdom had been reduced to a few hundred and there are good chances of eradicating the species from the wild in Europe by 2015” (Box 20.2, p. 495).

What happened next. - Numbers kept falling. European numbers in 2013 were “less than 7% of the 2000 population”. The authors added that “coordinated action is still required to achieve eradication”, and that the forthcoming EU instrument would be “an early test” with “the potential to achieve the first continental scale eradication of an invasive alien species” (Robertson et al., online 25 June 2014). - The species was on the first Union list (2016), so trade, keeping and release became illegal EU-wide. - The 2015 target was missed. - A Bern Convention progress report on a 2021–25 action plan records that “small populations of Ruddy Duck remain, mostly in Germany, France, Belgium, the Netherlands and the UK”. The report is Cranswick and Hall (2023), cited in Wanders and Hosner (5 March 2026); the CoE site could not be accessed directly. - The same 2026 paper reports a ruddy × white-headed duck hybrid culled in Denmark in February 2022, about 1,700 km from Spain’s white-headed duck population. - In 2023 the GB strategy spoke of “successful eradication programmes in place” for ruddy duck, which implies ongoing, not completed. - England’s general licence GL21 to kill or take ruddy ducks is still issued, for 1 January–31 December 2026 (GOV.UK). - The UK knock-down was real. News reports of 2012–2014 describe the British population cut from about 5,500 (2000) to tens of birds, at a cost of about GBP 5 million by 2012 (secondary sources, cited via Wikipedia; not independently checked).

Verdict: weakened. The UK reduction claim held up. The forecast of Europe-wide eradication by 2015 failed: the target was rolled into a 2021–25 plan, and remnant populations persisted in 2023.

Implications for weight. The case still supports the chapter’s broader points: - values and public reaction shape feasibility (the RSPB’s costly backing, p. 495); - coordinated, sustained culling can cut a continental population by more than 90%.

But it shows the “last mile” problem. Eradication across several jurisdictions stalls when effort is uneven between countries, and the final few per cent take longer than forecast (Robertson et al. 2015 note that control “varied widely between countries”). The general mechanism: under multi-party management, dated eradication targets are prone to slippage, and the laggard jurisdiction sets the pace. That is well evidenced here.

Claim 6: After the court case, the grey squirrel “is now expected to spread across Europe, with huge impacts”; it was still legally sold in Italian pet shops 12 years after the Bern Convention’s 1999 request (pp. 492, 495)#

Original claim. - Box 20.1 (p. 492): despite the Bern Convention’s 1999 request to eradicate and “prohibit the trade in the species”, “twelve years later it is still legally offered for sale in pet shops, while the invasive population continues to grow”. - Box 20.2 (p. 495): the prosecution of the eradication officers ruined the campaign, and “the grey squirrel is now expected to spread across Europe, with huge impacts on biodiversity as well as the economy of the entire region”.

What happened next. - Trade. Sciurus carolinensis was on the first Union list (Implementing Regulation 2016/1141, in force 3 August 2016). Trade, keeping, breeding and release became illegal across the EU, 17 years after the Bern request. I could not confirm whether Italy acted nationally before 2016. - The list’s lag shows up in a related species. Finlayson’s squirrel (Callosciurus finlaysonii) was still being sold in Italian pet shops in 2021, before it was listed in 2022 (Mazzamuto et al. 2021; Implementing Regulation 2022/1203). - A new population after the Bern request. A grey squirrel population near Perugia was founded by an intentional release in 2003 in a private wildlife park inside a Natura 2000 site, four years after the Bern request. It had spread over about 50 km² when an EU LIFE project (U‑SAVEREDS) set out to eradicate it (Cruciani et al. 2022). - Spread within Italy. - “Range expansion of grey squirrels is occurring, at different rates, in some areas in Italy (e.g. Piedmont, Lombardy, Veneto)”. This “generalised expansion” is attributed partly to “the low priority given to it by public administrators and/or politicians”. The Genoa Nervi population is noted as an exception, having been eradicated (Wauters et al. 2021). - New breeding nuclei were found in Tuscany and Veneto (Mori et al. 2016), and surveys continued in Tuscany in 2025 (conference abstract; title only). - Spread beyond Italy. - I found no report of established grey squirrel populations in France or Switzerland to date. - Using the European climatic niche, the potential range in Europe is “primarily Britain, Ireland, and Italy”. The same study found the range could be about 2.45 times larger if the species’ North American niche applied, with unfilled areas “primarily in France, Italy, Spain, Croatia, and Portugal” (Yang et al. 2023). - The spread forecast had a decades-long horizon (Bertolino et al. 2008; not re-read), so it cannot yet be judged failed. - A related Italian invader, Pallas’s squirrel, was recorded in 2021 in Magadino, Switzerland, about 20 km from its Italian population (Mazzamuto et al. 2021). This shows that cross-border movement of Italian squirrel invaders is possible. - An unexpected natural check elsewhere. In Ireland the grey squirrel’s advance “seems to have stopped, or even been reversed, apparently associated with an increase in the pine marten population” (Wauters et al. 2021). Pine marten recovery is now studied in Britain for the same effect (2025 conference abstract; title only).

Verdict: partly held up. - The trade complaint was resolved by EU law in 2016, late but decisively. - Continued spread within Italy was confirmed, as was policy neglect at regional level. - The spread across Europe has not happened in the 13 years since. The latest niche modelling suggests Europe-wide spread is possible but not assured.

Implications for weight. The case remains good evidence for two mechanisms the chapter identified: - Emotive values and litigation can derail an eradication at the critical early moment. The damage then compounds, and new deliberate releases continue (Perugia, 2003). - A harmful item stays legally on sale for years while public money pays to contain it. The listing of Finlayson’s squirrel repeats the pattern.

The strong forecast (“expected to spread across Europe”) should be cited as a projection, not an outcome. The Irish pine marten effect is a reminder that ecological context can change the trajectory in ways that neither side predicted.

Claim 7: Voluntary codes of conduct (horticulture, pets) “have so far had limited effectiveness and buy-in”; they lack sanctions and depend on promotion (pp. 493, 498)#

Original claim. “There is much reliance on voluntary codes of conduct which by definition lack sanctions for non-compliance” (p. 493). “Such approaches have so far had limited effectiveness and buy-in (Drew et al., 2010) … The effectiveness of such voluntary codes depends largely on how well they are promoted” (p. 498). Industry prefers “a voluntary approach with agreed codes of conduct to hard laws”, though some firms see legislation as fairer (p. 499).

What happened next. - Codes kept multiplying. They now cover botanic gardens (2013), hunting, recreational fishing, zoos and aquaria, boating, international travel and others (IPBES SPM Box 1). - IPBES agrees codes are insufficient alone but frames them more positively. Codes “have limits” but “can complement legislation”, and “are intended to complement, not replace, obligations within national legislation” (well established). IPBES also notes that “many agribusinesses do not manage the risk of the plants they trade”. The box showcases the Council of Europe codes, one of which Heywood co-authored. - The code author acknowledged the evidence gap. In 2014 Heywood wrote that codes “are of little value … without an effective ongoing implementation strategy” and that “little is known of the effectiveness of such approaches and critical assessments are needed” (EPPO Bulletin, 26 June 2014). - The EU moved to binding bans for listed species (claim 2). The Commission’s 2021 review credits the Regulation with the “removal of species from trade”. Horticulture and pets were the two pathways most Member States prioritised. - Binding bans also leak. - Belgium has had a voluntary horticulture code since 2009, plus the EU ban from 2015. In 2020 surveys, garden centres still sold four Belgian consensus-list species and three species of Union concern. Nearly all were mislabelled through misidentification or synonyms (Van den Neucker and Scheers 2022). The authors conclude that “regular surveys are essential to assess the effectiveness of voluntary codes of conduct and legal trade bans”. - California banned sale of nine Caulerpa species in late 2001. About four years later, 53% of surveyed aquarium stores still sold Caulerpa and four sold C. taxifolia; the authors concluded “the ban has not been effective” without enforcement and outreach (Diaz et al. 2012). - In the US, state plant regulatory lists are “reactive and inconsistent”, with on average only 16.8% overlap between neighbouring states’ lists (Beaury et al. 2021). - Binding bans can work when applied. Saskatchewan’s 2020 ban on marbled crayfish was followed by a significant fall in crayfish advertisements and sellers in the province, with no such change in other provinces (Faulkes and Xiao 2023, preprint).

Verdict: partly held up. - The claim that voluntary codes alone had limited effect is consistent with later assessments, and policy moved to binding bans as the chapter wanted. - But the evidence base remains thin: few rigorous evaluations exist, as a code author himself conceded. - Later evidence shows that binding bans also underperform without enforcement, monitoring and correct identification. The contrast between voluntary and mandatory is less sharp than the chapter implies.

Implications for weight. The transferable insight survives in a more precise form. Sanctionless self-regulation underperforms, but so does regulation that is not monitored. Compliance depends on detection capacity (inspection, labelling, taxonomy) as much as on legal form. The chapter’s observation that industries prefer codes, while some firms want binding rules to level the field (p. 499), fits the later shift to EU-wide bans.

Claim 8: Formal risk assessment of biocontrol agents “greatly reduce[s] the chance of unexpected behaviour”; the UK release of Aphalara itadori against Japanese knotweed (costing over GBP 150 million a year) was Europe’s first classical biocontrol release against an invasive plant (p. 496)#

Original claim. “The selection of an agent is nowadays carefully studied through formal risk assessment protocols … that greatly reduce the chance of unexpected behaviour of released species.” The knotweed psyllid A. itadori “was released in the United Kingdom … This represents the first classical biological control release against an invasive alien plant in Europe” (p. 496). The chapter also notes that EU rules on releasing agents are “quite stringent” while rules on invasive species were “non-existent” (p. 496).

What happened next. - The safety claim is well supported. - A systematic review found that more than 99% of 512 weed biocontrol agents released worldwide had no known significant non-target effects on plants. The largest impacts came from two old introductions that “would not be permitted today” (Suckling and Sforza, 13 January 2014). - IPBES (2023): risk-based frameworks under the IPPC “have been applied and continue to be effective” (well established). Biocontrol has succeeded in “more than 60 per cent of documented cases” for invasive plants and invertebrates. - The flagship case did not deliver. - Fung et al. (2020): “this potential has not materialised in the field where long-term establishment of A. itadori has been unsuccessful”. - Post-release work in the UK examined how rainfall, competition and generalist predators limit establishment (Clewley 2015, PhD thesis). - North America shows the same pattern: predation and climate limit establishment (Andersen and Elkinton 2022), and “limited establishment from widespread releases” in the USA (Grevstad et al., November 2025; title only). - Climate matching suggests the Kyushu strain first released in the UK came from a source locality with “little-to-no suitability” for European knotweeds (Andersen and Elkinton 2023). - The Netherlands approved release of a new Murakami strain in 2020. In trials it cut rhizome biomass by about 35–50% on two knotweed species (Camargo et al. 2022). I found no field-establishment result. - The knotweeds became regulated. They were added to the EU Union list only in the July 2025 update. - Biocontrol in Europe grew modestly. In 2023 there were “only five active programmes” in Europe (Lesieur et al. 2023). Programmes against aquatic weeds (Azolla, Crassula helmsii, Hydrocotyle) are now in field release in Great Britain and northern Europe (Pratt et al., August 2026). - The regulatory asymmetry the chapter noted persists as a live complaint. A September 2026 paper is titled “Reducing regulatory constraints: Reestablishing classical biological control…” (Urbaneja et al.; title only).

Verdict: partly held up. The general safety claim for risk-assessed biocontrol held up well. The flagship knotweed release had not established in the UK field a decade after release (Fung et al. 2020), and I found no later report of establishment or field control. The chapter presented the release as a milestone without claiming success, but readers should not take it as evidence of efficacy.

Implications for weight. Two lessons, both technology-neutral: - Precautionary pre-release assessment can achieve a strong safety record (over 99% without significant non-target harm). The chapter was right to contrast this with the absence of rules for known invaders. - Assessment for safety is not assessment for efficacy. An agent can pass every safety test and still fail to work. It can also be judged by stricter rules than the harm it addresses; the chapter’s asymmetry point is still being argued in 2026.

Claim 9: Novel biofuel and biomass crops “present a risk of favouring new invasions”; synthetic biology “may in the near future produce still more fundamentally novel species”; assisted migration carries invasion risk; future montane invaders may be mountain specialists introduced directly (pp. 495, 501)#

Original claim. See the heading (p. 495). On p. 501, “in montane areas, future invaders may be mountain specialists directly introduced through human activity between high-elevation habitats”. The chapter expects “a wider and more intense debate” on biofuel crop planting and managed relocation.

What happened next. - Biofuel crops: the risk was recognised in regulation, but I found little evidence of new invasions. - The US EPA approved giant reed (Arundo donax) and napier grass as cellulosic biofuel feedstocks on 11 July 2013. “In response to comments … concerning the potential for these crops to behave as invasive species”, it added registration, record-keeping and reporting requirements (78 FR 41703). - A 2015 CABI volume framed the question as “sustainable resources or the next great invasion?” and called for multi-year, multi-site empirical studies (Quinn, Barney and Matlaga 2015). - A. donax remains one of the “100 worst” invaders that “easily escapes from cultivation” (Kato-Noguchi and Kato 2025). But I found no documented large new European invasion traceable to purpose-grown bioenergy plantings since 2013. - Neither A. donax nor Miscanthus is on the EU Union list. - Synthetic biology: the prediction has not materialised in the form stated, and the direction reversed. - I found no documented invasion by an engineered organism. - Instead, the field has moved to using genetic tools against invaders. IUCN assessed synthetic biology for conservation in 2019 (Genetic frontiers for conservation; not read in full). Island rodent eradication is modelled with gene drives and “self-limiting” genetic biocontrol, whose “ecological and regulatory implications are still in active debate” (Birand et al., April 2026). - This brings the chapter’s own warning about fixes becoming hazards (p. 497) to a new class of tools. - Assisted migration: the debate the chapter expected happened, but it is unresolved. - IUCN published translocation guidelines in 2013. - A 2025 paper co-authored by Genovesi notes that “none [of the existing guidelines] allow case-specific decision-making based on risks and benefits”. It proposes a risk-benefit framework (D’Andrea et al. 2025). - Assisted migration of forest trees is expanding in European forestry practice (Dimitrova et al. 2026). Historical introductions show real hybridisation with native trees (Caucasian × European beech; Stefanini et al. 2026). - Mountains: invasion is increasing, but by the pathway the chapter described as the present one. - Repeated surveys along mountain roads in 11 regions found the number of non-native species rising about 16% per decade, with upward range shifts in 10 of 11 regions (Iseli et al. 2023). This is lowland species spreading up. - A 2026 review notes 771 alien taxa in the Pyrenees (Nualart et al. 2026). - I found no evidence confirming or refuting the specific “mountain specialists” forecast.

Verdict: unclear. These were statements of risk, not firm predictions, and most remain untested: - the biofuel concern was taken up in regulation, but no major resulting invasions are documented in the sources checked; - the synthetic biology concern is still speculative, and the technology is now aimed at invaders; - the assisted migration debate the chapter predicted did occur; - mountain invasion is rising, as the chapter implied, but the specific mechanism it forecast is unverified.

Implications for weight. These are good examples of horizon scanning: they flagged blind spots where policy incentives, such as renewable energy mandates or conservation goals, create new introduction pathways. They should carry weight as prompts, not as evidence of harm. The most useful transferable point: interventions justified by one environmental goal (energy, climate adaptation, pest control) can open new pathways for a different harm. That is the chapter’s “fixes that became hazards” mechanism (p. 497), and it recurs across the post-2013 record.

Claim 10: A shift from species-by-species inspection to pathway-based regulation of plants for planting, modelled on wood packaging, will reduce the risk from unknown as well as known pests (pp. 498–499)#

Original claim. “A species-by-species regulatory approach relying on inspections is more and more difficult … the forest entomology and pathology science communities recommend a pathway approach for regulating nursery stock, similar to that adopted for wood packaging material … best management practices that effectively prevent known IAS will significantly reduce the risk of also introducing unknown pests. In this regard, the IPPC is developing an international standard for plants for planting” (pp. 498–499).

What happened next. - The standard existed before the report appeared. ISPM 36 (Integrated measures for plants for planting) was adopted by CPM‑7 in March 2012. It applies a pathway (“integrated measures”) approach at the place of production (IPPC/FAO text). The chapter’s “is developing” was already out of date on publication. - The EU went further, with a reverse-onus mechanism. - Regulation (EU) 2016/2031 (applied from 14 December 2019) created “high-risk plants” (Art. 42): items that on preliminary assessment pose unacceptable risk “shall not be introduced” pending full risk assessment. - The first list (Implementing Regulation 2018/2019) provisionally prohibited plants for planting of 34 woody genera plus one species (Ficus carica), including Acer, Quercus, Prunus, Fraxinus and Ulmus, from all third countries. EFSA commodity risk assessments to lift or confirm these continue into 2026. - For its genera, this is effectively a “safe until shown otherwise” approach. It goes beyond what the chapter proposed. - Evidence on the model the chapter cites. US interception data showed wood packaging infestation rates fell by 36–52% after ISPM 15 was implemented, a real but partial effect against the goal to “practically eliminate” the risk. The authors noted a “paucity of international interception data” for evaluating it (Haack et al., 14 May 2014). - The plants-for-planting pathway is still leaky. - EU imports in 2005–2014 totalled over 30 billion plants across more than 7,500 genus-origin commodities, and “two-thirds of the imported commodities changed every year”. That supports the chapter’s claim that item-by-item inspection cannot keep up (Eschen et al. 2017). - The Xylella fastidiosa strain devastating Apulian olives (detected 2013) is genetically closest to Costa Rican isolates (Giampetruzzi et al. 2017). That is consistent with arrival on imported live plants, though the paper itself does not identify the pathway. - A 2016 survey reported “widespread Phytophthora infestations in European nurseries” (Jung et al. 2016; title only). - IPBES (2023) finds that pathway management, including systems approaches, has “increased interception rates and slowed the rate of invasive alien species arriving” (well established), citing the brown marmorated stink bug in Australasia. - I found no study isolating the effect of ISPM 36 itself.

Verdict: partly held up. The recommended shift happened in international standards (2012) and, more strongly, in EU law (2019). The rationale (turnover in trade and unknown organisms defeat species lists) was reinforced by later evidence (Seebens et al. 2018; Eschen et al. 2017). Evidence that pathway rules have cut arrivals is real for wood packaging but partial, and specific evidence for plants for planting is lacking.

Implications for weight. This is one of the chapter’s most transferable insights. When risk scales with the volume and turnover of a trade, and many hazards are unknown in advance, regulating the pathway beats inspecting items. Later practice shows the next step the chapter did not name: provisional prohibition pending assessment, which reverses the burden of proof for defined high-risk categories. The evidence caveat also transfers. Pathway rules are adopted on strong logic, but their measured effects are modest and rarely evaluated, because before-and-after monitoring is seldom built in.

What this means for the section as a whole#

Each was tested or strengthened after 2013 and is now the mainstream position (IPBES 2023; the global biodiversity framework’s Target 6). But much of that mainstream was shaped by the chapter’s own authors. - Right in direction, optimistic on timing: the institutional forecasts (claims 2, 5, 6). - The EU instrument came about a year late and was implemented slowly. - Ruddy duck eradication missed 2015 by more than a decade. - Grey squirrel trade was stopped only in 2016, and the predicted spread across Europe has not yet happened.

The chapter’s own late lesson, that coordination and consensus arrive slowly, applies to its forecasts too. - Weakest: - the monetary claims (claim 3), especially the misattributed global USD 1.4 trillion/5% of GDP figure, which later databases do not support; - the showcase examples offered as achievements or missed chances (claim 8’s knotweed psyllid; claim 4’s French Caulerpa). - Refined by later evidence: the claim about voluntary versus binding approaches (claim 7). Codes did underperform, but binding bans also leak without monitoring, enforcement and correct identification. - Mechanisms the post-2013 record adds or sharpens: 1. List lag and list exclusion. Risk-assessed prioritised lists take three or more years per item and leave harmful but unlisted items legal (knotweed listed in 2025; Finlayson’s squirrel sold until 2022). 2. Delivery gaps below the coordinating level. Most Member States had not delivered pathway plans by 2021; there were infringement procedures and a CJEU judgment (2024). 3. The “last mile” in eradication across several jurisdictions. Remnant ruddy duck populations persist in several countries. 4. Safety versus efficacy. A risk-assessed control agent can be safe and still ineffective. 5. Boom-bust dynamics. They complicate retrospective “missed opportunity” judgements without undermining the case for early action. 6. Reverse-onus pathway rules. EU “high-risk plants” provisions go beyond the chapter’s proposals.

Sources#

Global trends and assessments - Seebens, H. et al. (15 February 2017), “No saturation in the accumulation of alien species worldwide”, Nature Communications 8: 14435. https://doi.org/10.1038/ncomms14435 - Seebens, H. et al. (2018), “Global rise in emerging alien species results from increased accessibility of new source pools”, PNAS. https://doi.org/10.1073/pnas.1719429115 - Seebens, H. et al. (online October 2020; 2021 issue), “Projecting the continental accumulation of alien species through to 2050”, Global Change Biology. https://doi.org/10.1111/gcb.15333 - Seebens, H. et al. (12 August 2025), “Biological invasions: a global assessment of geographic distributions, long-term trends, and data gaps”, Biological Reviews. https://doi.org/10.1111/brv.70058 - Bonnamour, A., Gippet, J. M. W. and Bertelsmeier, C. (2021), “Insect and plant invasions follow two waves of globalisation”, Ecology Letters. https://doi.org/10.1111/ele.13863 - Tedeschi, L. et al. (2022), “Introduction, spread, and impacts of invasive alien mammal species in Europe”, Mammal Review. https://doi.org/10.1111/mam.12277 - IPBES (4 September 2023), media release on the Invasive Alien Species Assessment. https://www.ipbes.net/IASmediarelease - IPBES (2023), Summary for Policymakers of the Thematic Assessment Report on Invasive Alien Species and their Control (Roy, H. E. et al., eds). https://doi.org/10.5281/zenodo.7430692 (text read from Zenodo record 11254974, https://zenodo.org/records/11254974) - Convention on Biological Diversity, Kunming-Montreal Global Biodiversity Framework (adopted 19 December 2022), Target 6. https://www.cbd.int/gbf/targets/6 - GOV.UK (27 February 2023), “New strategy launched to protect biodiversity and economy from non-native species”. https://www.gov.uk/government/news/new-strategy-launched-to-protect-biodiversity-and-economy-from-non-native-species

EU law and implementation - European Commission (9 September 2013), Proposal for a Regulation on the prevention and management of the introduction and spread of invasive alien species, COM(2013) 620 final. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:52013PC0620 - Regulation (EU) No 1143/2014 of 22 October 2014 on the prevention and management of the introduction and spread of invasive alien species, OJ L 317, 4.11.2014 (in force 1 January 2015). https://eur-lex.europa.eu/eli/reg/2014/1143/oj - Commission Implementing Regulation (EU) 2016/1141 of 13 July 2016 (first Union list). https://eur-lex.europa.eu/eli/reg_impl/2016/1141/oj ; amended by 2017/1263 (12 July 2017), 2019/1262 (25 July 2019), 2022/1203 (12 July 2022) and 2025/1422 (17 July 2025), https://eur-lex.europa.eu/eli/reg_impl/2025/1422/oj ; consolidated text of 7 August 2025: https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:02016R1141-20250807 - European Commission (13 October 2021), Report on the review of the application of Regulation (EU) No 1143/2014, COM(2021) 628 final. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:52021DC0628 - European Commission, “Invasive alien species” (accessed 25–26 September 2026). https://environment.ec.europa.eu/topics/nature-and-biodiversity/invasive-alien-species_en - Court of Justice of the EU (14 November 2024), Case C‑165/23, Commission v Bulgaria; summary OJ C/2025/130. https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:62023CA0165 - Court of Justice of the EU (6 June 2025), Case C‑205/24, Commission v Ireland, order (text not read). https://eur-lex.europa.eu/legal-content/EN/TXT/?uri=CELEX:62024CB0205 - Kurtul, I. et al. (8 July 2024), “The need of centralized coordination to counter biological invasions in the European Union”, Environmental Sciences Europe. https://doi.org/10.1186/s12302-024-00955-0 - Kumschick, S. et al. (2 February 2024), “Considerations for developing and implementing a safe list for alien taxa”, BioScience. https://doi.org/10.1093/biosci/biad118

Costs - Diagne, C. et al. (2020), “InvaCost, a public database of the economic costs of biological invasions worldwide”, Scientific Data 7: 277. https://doi.org/10.1038/s41597-020-00586-z - Diagne, C. et al. (31 March 2021), “High and rising economic costs of biological invasions worldwide”, Nature. https://doi.org/10.1038/s41586-021-03405-6 ; Author Correction (10 August 2022): https://doi.org/10.1038/s41586-022-05100-6 - Haubrock, P. J. et al. (29 July 2021), “Economic costs of invasive alien species across Europe”, NeoBiota 67. https://doi.org/10.3897/neobiota.67.58196 - Henry, M. et al. (8 June 2023), “Unveiling the hidden economic toll of biological invasions in the European Union”, Environmental Sciences Europe. https://doi.org/10.1186/s12302-023-00750-3 - Cuthbert, R. N. et al. (2022), “Biological invasion costs reveal insufficient proactive management worldwide”, Science of the Total Environment. https://doi.org/10.1016/j.scitotenv.2022.153404 - Ahmed, D. A. et al. (2022), “Managing biological invasions: the cost of inaction”, Biological Invasions. https://doi.org/10.1007/s10530-022-02755-0 - Ahmed, D. A. et al. (July 2026), “Projecting future damage costs of non-native species using combined dynamical and cost-density equations”, Ecological Applications. https://doi.org/10.1002/eap.70252 - Caetano, G. et al. (4 March 2025, preprint), “Global extrapolation drastically increases estimated economic costs of biological invasions”, Research Square. https://doi.org/10.21203/rs.3.rs-5825547/v1 - Pimentel, D. et al. (2001), “Economic and environmental threats of alien plant, animal, and microbe invasions”, Agriculture, Ecosystems & Environment 84: 1–20 (text not accessible for this check). https://doi.org/10.1016/S0167-8809(00)00178-X - Pimentel, D., Zuniga, R. and Morrison, D. (2005), “Update on the environmental and economic costs associated with alien-invasive species in the United States”, Ecological Economics 52: 273–288 (text not accessible for this check). https://doi.org/10.1016/j.ecolecon.2004.10.002

Early action and Caulerpa - Pluess, T. et al. (2012), “When are eradication campaigns successful? A test of common assumptions”, Biological Invasions. https://doi.org/10.1007/s10530-011-0160-2 - Diaz, S. et al. (22 April 2012), “Effectiveness of the California state ban on the sale of Caulerpa species in aquarium retail stores in southern California”, Environmental Management. https://doi.org/10.1007/s00267-012-9860-3 - Tejada, S. et al. (19 July 2013), “A new approach using biomarkers to elucidate the regression state of the invasive alga Caulerpa taxifolia in waters around the Balearic Islands”, Marine and Freshwater Research. https://doi.org/10.1071/MF13012 - Montefalcone, M. et al. (online 26 May 2015), “A tale of two invaders: divergent spreading kinetics of the alien green algae Caulerpa taxifolia and Caulerpa cylindracea”, Biological Invasions. https://doi.org/10.1007/s10530-015-0908-1 - Meinesz, A. et al. (30 July 2026), “Caulerpa taxifolia var. distichophylla … a new invasive species on the French Mediterranean coast”, Cryptogamie, Algologie. https://doi.org/10.5252/cryptogamie-algologie2026v47a3 - Strayer, D. L. et al. (2017), “Boom-bust dynamics in biological invasions: towards an improved application of the concept”, Ecology Letters. https://doi.org/10.1111/ele.12822

Ruddy duck - Robertson, P. A. et al. (online 25 June 2014; 2015 issue), “Towards the European eradication of the North American ruddy duck”, Biological Invasions. https://doi.org/10.1007/s10530-014-0704-3 - Wanders, K. and Hosner, P. A. (5 March 2026), “A Ruddy Oxyura jamaicensis × White-headed Duck O. leucocephala hybrid diagnosed in Denmark”, Bulletin of the British Ornithologists’ Club 146(1), citing Cranswick, P. A. and Hall, C. (2023), Eradication of the Ruddy Duck in the Western Palaearctic: 2023 progress report on implementation of the 2021–25 action plan, report to the Bern Convention (WWT). https://doi.org/10.25226/bboc.v146i1.2026.a6 - GOV.UK (1 January 2026), “Ruddy ducks: licence to kill or take them (GL21)”. https://www.gov.uk/government/publications/ruddy-ducks-licence-to-kill-or-take-them - Wikipedia, “Ruddy duck” (secondary; used only for the 2012–2014 UK news figures it cites from The Guardian, 8 March 2012, and The Telegraph, 8 February 2014). https://en.wikipedia.org/wiki/Ruddy_duck

Grey squirrel and other squirrels - Mori, E. et al. (June 2016), “Alien shades of grey: new occurrences and relevant spread of Sciurus carolinensis in Italy”, European Journal of Ecology. https://doi.org/10.1515/eje-2016-0002 - Wauters, L. A. et al. (2021), “A golden cage for the European red squirrel in Italy? Proposal for a targeted control of the grey squirrel”, Biodiversity. https://doi.org/10.1080/14888386.2021.1927843 - Mazzamuto, M. V. et al. (2021), “Exotic pet trade as a cause of biological invasions: the case of tree squirrels of the genus Callosciurus”, Biology 10: 1046. https://doi.org/10.3390/biology10101046 - Cruciani, D. et al. (12 October 2022), “Health status of the eastern grey squirrel (Sciurus carolinensis) population in Umbria: results of the LIFE project ‘U-SAVEREDS’”, Animals 12: 2741. https://doi.org/10.3390/ani12202741 - Yang, R. et al. (2023), “Climatic niche and range shifts of grey squirrels (Sciurus carolinensis Gmelin) in Europe”, Pest Management Science. https://doi.org/10.1002/ps.7554 - Avetta et al. (2025), “Assessing the presence of grey squirrel (Sciurus carolinensis) in Tuscany: a survey using hair tubes”, conference abstract (title only). https://doi.org/10.20315/evmc.2025.152 - Scopes et al. (2025), “The recovery of pine marten (Martes martes) in Britain and implications for grey squirrel management”, conference abstract (title only). https://doi.org/10.20315/evmc.2025.052

Codes of conduct and trade bans - Heywood, V. H. (26 June 2014), “Voluntary codes of conduct for botanic gardens and horticulture and engagement with the public”, EPPO Bulletin. https://doi.org/10.1111/epp.12112 - Van den Neucker, T. and Scheers, K. (2022), “Mislabelling may explain why some prohibited invasive aquatic plants are still being sold in Belgium”, Knowledge & Management of Aquatic Ecosystems. https://doi.org/10.1051/kmae/2022005 - Beaury, E. M. et al. (2021), “Plant regulatory lists in the United States are reactive and inconsistent”, Journal of Applied Ecology. https://doi.org/10.1111/1365-2664.13934 - Faulkes, Z. and Xiao (6 June 2023, preprint), “Online advertisements for crayfish decrease after a provincial ban”, ARPHA Preprints. https://doi.org/10.3897/arphapreprints.e107487

Biological control - Suckling, D. M. and Sforza, R. F. H. (13 January 2014), “What magnitude are observed non-target impacts from weed biocontrol?”, PLoS ONE 9: e84847. https://doi.org/10.1371/journal.pone.0084847 - Clewley, G. (2015), Post-release assessment of Aphalara itadori as a classical biological control agent of Fallopia japonica, PhD thesis, Imperial College London. https://doi.org/10.25560/23232 - Fung, C. et al. (July 2020), “Effect of humidity and temperature on the performance of three strains of Aphalara itadori”, Biological Control. https://doi.org/10.1016/j.biocontrol.2020.104269 - Andersen, J. C. and Elkinton, J. S. (2022), “Predation and climate limit establishment success of the Kyushu strain of … Aphalara itadori … in the northeastern United States”, Environmental Entomology. https://doi.org/10.1093/ee/nvac031 - Andersen, J. C. and Elkinton, J. S. (12 September 2023), “Climate suitability analyses compare the distributions of invasive knotweeds in Europe and North America with the source localities of their introduced biological control agents”, Ecology and Evolution. https://doi.org/10.1002/ece3.10494 - Camargo, A. M. et al. (November 2022), “A new population of the biocontrol agent Aphalara itadori performs best on the hybrid host Reynoutria × bohemica”, Biological Control. https://doi.org/10.1016/j.biocontrol.2022.105007 - Grevstad, F. S. et al. (9 November 2025), “Limited establishment from widespread releases of the knotweed psyllid Aphalara itadori … in the USA”, BioControl (title only). https://doi.org/10.1007/s10526-025-10362-w - Lesieur, V. et al. (12 April 2023), “Prioritising environmental invasive weeds of European concern for classical biological control: a reanalysis”, Weed Research. https://doi.org/10.1111/wre.12582 - Pratt, C. et al. (17 August 2026), “Classical biological control of invasive aquatic weeds in Great Britain and Europe”, ARPHA Conference Abstracts 9. https://doi.org/10.3897/aca.9.e204108 - Urbaneja, A. et al. (23 September 2026), “Reducing regulatory constraints: Reestablishing classical biological control for management of invasive arthropods and weeds”, Entomologia Generalis (title only). https://doi.org/10.1127/entomologia/4578

Novel pathways (biofuels, synthetic biology, assisted migration, mountains) - US EPA (11 July 2013), final rule approving renewable fuel pathways for giant reed (Arundo donax) and napier grass, 78 FR 41703. https://www.federalregister.gov/documents/2013/07/11/2013-16488/regulation-of-fuels-and-fuel-additives-additional-qualifying-renewable-fuel-pathways-under-the - Quinn, L. D., Barney, J. N. and Matlaga, D. P. (2015), “The bioenergy landscape: sustainable resources or the next great invasion?”, in Bioenergy and Biological Invasions (CABI). https://doi.org/10.1079/9781780643304.0001 - Kato-Noguchi, H. and Kato, M. (14 July 2025), “The invasive mechanism and impact of Arundo donax”, Plants 14: 2175. https://doi.org/10.3390/plants14142175 - IUCN (2019), Genetic frontiers for conservation: an assessment of synthetic biology and biodiversity conservation (not read in full). https://doi.org/10.2305/IUCN.CH.2019.05.en - Birand, A. et al. (19 April 2026), “The LAST Mile: evaluating genetic biocontrol as a supplemental tool for eradicating invasive rodents on islands”, Evolutionary Applications. https://doi.org/10.1111/eva.70238 - D’Andrea, R. et al. (November 2025), “Ecological risk-benefit analysis for assisted colonization”, Global Change Biology. https://doi.org/10.1111/gcb.70613 - Stefanini, C. et al. (10 August 2026), “Hybrid vigor and outbreeding depression after 100 years of replicate introduction of Caucasian beech to European forests”, Heredity. https://doi.org/10.1038/s41437-026-00860-7 - Dimitrova, A. et al. (September 2026), “Towards resilient forest establishment in Europe: functional traits, genetic diversity and multifunctional design”, New Forests (abstract via Europe PMC). - Iseli, E. et al. (26 January 2023), “Rapid upwards spread of non-native plants in mountains across continents”, Nature Ecology & Evolution. https://doi.org/10.1038/s41559-022-01979-6 - Nualart, N. et al. (13 February 2026), “Plant invasions in mountain areas: global and Mediterranean perspectives”, Plants 15: 588. https://doi.org/10.3390/plants15040588

Pathways and plant health - IPPC/FAO, ISPM 36, Integrated measures for plants for planting (adopted by CPM‑7, March 2012). https://www.ippc.int/en/publications/636/ ; text: https://www.fao.org/3/k8114e/k8114e.pdf - Regulation (EU) 2016/2031 of 26 October 2016 on protective measures against pests of plants (applies from 14 December 2019). https://eur-lex.europa.eu/eli/reg/2016/2031/oj - Commission Implementing Regulation (EU) 2018/2019 of 18 December 2018 establishing a provisional list of high-risk plants. https://eur-lex.europa.eu/eli/reg_impl/2018/2019/oj - Haack, R. A. et al. (14 May 2014), “Effectiveness of the International Phytosanitary Standard ISPM No. 15 on reducing wood borer infestation rates in wood packaging material entering the United States”, PLoS ONE 9: e96611. https://doi.org/10.1371/journal.pone.0096611 - Eschen, R. et al. (November 2017), “A risk categorisation and analysis of the geographic and temporal dynamics of the European import of plants for planting”, Biological Invasions. https://doi.org/10.1007/s10530-017-1465-6 - Giampetruzzi, A. et al. (2017), “Genome-wide analysis provides evidence on the genetic relatedness of the emergent Xylella fastidiosa genotype in Italy to isolates from Central America”, Phytopathology. https://doi.org/10.1094/PHYTO-12-16-0420-R - Jung, T. et al. (2016), “Widespread Phytophthora infestations in European nurseries put forest, semi-natural and horticultural ecosystems at high risk of Phytophthora diseases”, Forest Pathology (title only). https://doi.org/10.1111/efp.12239