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Assessing environmental risks of invasive species using ISPM 11: where to start

Mary Megan Quinlan, Nick M. Pasiecznik and Soetikno S. Sastroutomo

M.M. Quinlan, N.M. Pasiecznik: CAB International, UK; S.S. Sastroutomo: CAB International, SE Asia Regional Centre, P.O. Box 210, 43400 UPM Serdang, Selangor, Malaysia; e-mail:


Over the short history of the use of pest risk analysis as a harmonized approach to decision-making in plant health, several relevant international standards for phytosanitary measures (ISPMs) have been endorsed; more are approaching endorsement. Primary among these standards is the revision of ISPM 11 clarifying the scope of coverage for national plant protection organizations to include uncultivated plant systems. Historically, the emphasis of these organizations has been on protecting agriculture from pests. Now, with this suite of current and coming ISPMs to use, many countries will be wondering when and how to apply the expanded guidance on environmental risks. This paper discusses approaches for scoping environmental risks before applying the pest risk analysis process. It also considers more complicated issues that may arise in a pest risk analysis, such as indirect or secondary effects from the introduction of the species in question.


Recent changes to international plant protection guidelines have aimed to bring together common principles relating to biological diversity and the environment with the existing quarantine and plant health frameworks. These developments are of special interest to many individuals and organizations involved in plant health and ecology. This paper focuses on the 2003 revision of an international standard for phytosanitary measures, namely ISPM 11 rev. 1: Pest risk analysis for quarantine pests including analysis of environmental risks, and aims to show how national plant protection organizations that have little experience with environmental issues and limited resources may implement the changes introduced by the revision. (Note that after the date of the workshop on which this publication is based, the 2003 standard referred to in this paper and described here as the “revised ISPM 11” has subsequently been further supplemented and integrated to become ISPM 11 [2004].)

It is also important that the ecology sector appreciates these changes in guidelines and fully participates in implementing them. Many ecologists and others working on environmental issues still fail to appreciate the NPPOs’ wealth of experience in preventing introductions of unwanted exotic species. However, the majority of NPPOs will lack the resources either to conduct their own ecological research or to interpret a mass of information on ecological interactions. NPPOs facing an expanded scope of responsibility need the cooperation of ecologists who are willing to simplify their findings to the most likely scenarios and commonly agreed opinions.

A general framework is well established for evaluating risk and imposing measures to address that risk (see CABI, 2004; Quinlan, 2001). For the purpose of making regulatory decisions regarding trade or other pathways of entry, the process of pest risk analysis requires modification only, rather than any reinvention. While the Convention on Biological Diversity promotes an “ecosystem approach”, for example in decision II/8 (CBD, 1995) and decision V/6 (CBD, 2000), there is no specific guidance that betters that of ISPMs on how to use the information available to make timely decisions about potential threats to plants and plant communities from international trade (Quinlan, 2001).

Current guidelines for pest risk analysis

Pest risk analysis is a framework for organizing biological and other scientific and economic information. From this information we calculate risk, which is essentially the probability of an unwanted event or hazard occurring multiplied by the magnitude of the consequences if it does happen. This assessment of risk is used to identify appropriate measures to reduce risk to an acceptable level.

Even if the probability of an introduction of a pest is the same for two different countries, the risk may vary widely because the consequences for one country may be very different from the consequences in another country. The concept of consequences suggests a value judgement (Mumford, 2001). There is also a value judgement as to when an NPPO conducts a pest risk analysis.

The use of a harmonized approach to risk analysis is still relatively new for plant health, with little more than a decade in practice (see NAPPO, 1993). It is not surprising, therefore, that most of the relevant ISPMs are very recent and somewhat unproven as to the extent of their application, both geographically and topically.

The earliest ISPM on the topic, ISPM 2: Guidelines for pest risk analysis, is now out of date and undergoing revision because of concepts introduced by the Agreement on the Application of Sanitary and Phytosanitary Measures (WTO, 1994) and subsequent other ISPMs.

The original ISPM 11 [2001]: Pest risk analysis for quarantine pests was devised principally for quarantine pests of agriculture and forestry pests. As described in chapter 1, decisions relating to invasive species made by the Third Interim Commission on Phytosanitar Measures (FAO, 2001) led to preparation of a supplement to ISPM 11 on analysis of environmental risks. The version of the supplement that was endorsed (FAO, 2003) provides more detailed guidance on the analysis of the consequences for the environment and biodiversity of the introduction of quarantine pests; this analysis forms part of the assessment of potential economic consequences described in the standard. The revised ISPM 11 addresses the full range of pests covered by the IPPC. Contracting parties now agree that the scope of the convention includes pests that directly affect uncultivated plants, pests that indirectly affect plants and pests that affect plants through their effects on other organisms (as outlined in annex 1 of the 2003 revision of ISPM 11).

The international glossary of phytosanitary terms, ISPM 5, has been supplemented in 2001 with Guidelines on the interpretation and application of the concept of official control for regulated pests and in 2003 with Guidelines on the understanding of potential economic importance and related terms including reference to environmental considerations. These supplements have helped clarify what should be covered by pest risk analysis, and the range of domestic actions that may determine the regulatory status of a pest and the actors who may perform them.

Since September 2003 (the date of the meeting on which this publication is based), issues relating to pest risk analysis continue to feature in further work on development of new standards and revision of existing standards. In 2004, ISPM 21: Pest risk analysis for regulated non-quarantine pests was adopted. As already mentioned, ISPM 2 is under revision. ISPM 3: Code of conduct for the import and release of exotic biological control agents, originally published in 1996, has undergone draft revision and has been sent to members for country consultation under the title “Guidelines for the export, shipment, import and release of biological control agents and beneficial organisms”. Although ISPM 3 was originally very weak on guidance for the risk analysis aspect of a decision regarding import and release of a biocontrol agent, it has been judged to be robust in guidance on responsibilities of the various parties, documentation requirements for decision-making and facilitation of regional decisions (Kairo, Cock and Quinlan, 2003). In the revision, greater guidance on the risk analysis process per se is expected either to become integrated into the main text or to be supported through a separate guideline or an annex approach, such as that now established for ISPM 15: Guidelines for regulating wood packaging material in international trade and ISPM 18: Guidelines for the use of irradiation as a phytosanitary measure, which allow for additions of technical details as they become available (Quinlan et al., 2003).

Finally, there are ISPMs that will support the design of risk management measures or a combination of measures. These will be particularly important as NPPOs look at regulation of environmental pests. Such standards include the existing ISPM 14: The use of integrated measures in a systems approach for pest risk management, a draft standard on equivalence undergoing country consultation in 2004 under the title “Guidelines on the concept of equivalence of phytosanitary measures and its application in international trade” and a draft standard on efficacy of phytosanitary measures. The first ISPM regarding management of a particular pathway is ISPM 15 for wood packaging material in international trade. There will be more of these pathway- or commodity-specific ISPMs as the initial need for standards providing concept guidance is satisfied.

While this paper focuses on the 2003 revised ISPM 11, that ISPM is part of the suite of ISPMs on pest risk analysis. Other ISPMs directly impact or support pest risk analysis in terms of either the level of risk of entry or the options for risk management. For example, ISPM 6: Guidelines for surveillance and ISPM 17: Pest reporting provide critical information for determining risk. Other measures in ISPM 7: Export certification system, ISPM 12: Guidelines for phytosanitary certificates, ISPM 10: Requirements for the establishment of pest free places of production and pest free production sites or ISPM 4: Requirements for the establishment of pest free areas are designed to lower risk in the country of origin. The use of treatments employing irradiation in ISPM 18 or those prescribed for wood packaging in ISPM 15 reduce risk at the onset. The use of a systems approach to risk management (ISPM 14) rather than individual measures broadens the options for mitigation of risk considerably. Notification of non-compliance in ISPM 13: Guidelines for the notification of non-compliance and emergency action provides the feedback for evaluating and improving on risk management measures that are in place.

NPPOs, therefore, cannot apply only one ISPM in isolation from the other guidance. This may introduce the dilemma of when the revised ISPM 11 should be used as the main decision-making tool. It is worth remembering that the pest risk analysis supports the design and focus of an NPPO’s efforts based on actual risk, so that the most can be gained from the resources available.

Identifying species or pathways that pose an environmental risk

Plant health departments have an established system for the classification of pests of potential economic significance, generally arthropods and pathogens affecting agriculture or forestry (Mumford, 2001; Ebbels, 2003). However, this has been tested with the introduction of two relatively new issues: the need to protect the environment, and the need to consider far more complex interactions or impacts than the well-established agricultural costs due to pests. For NPPOs lacking the resources to address these issues fully and immediately, different approaches might be considered for the purposes of developing an overall PRA strategy to the management of invasive alien species. Three approaches, summarized below, are:

Monitor and regulate taxa and pathways not previously covered

One approach to identifying species or pathways that pose an environmental risk is to expand monitoring and regulation to cover taxa and their related pathways that may not have been covered previously (see CABI, 2004). This is particularly pertinent in a country that has not had legislation covering weeds. There is substantial information available about species of plants that have “escaped” their intended use and become countryside weeds. There is also considerable information about characteristics of plants that may cause the species to become more invasive than in its native environment (e.g. Pheloung, 1995; Parker, 2001; National Academies Committee, 2002). These characteristics may be debated, but there is now sufficient information for an NPPO to set up a quick screening process or a partial pest risk analysis on all plant species imported for planting (e.g. Groves, Panetta and Virtue, 2003). If a species is found to be suspicious, a full pest risk analysis may be required. Adding new taxa to the PRA process is a simple approach, familiar to most NPPOs, which can be built upon over the years as resources permit.

It is very important to note that conducting a pest risk analysis for a “high risk” genus or species does not necessarily mean that the NPPO will decide to restrict entry of that potential quarantine pest. This is where, again, the value judgement arises because many invasive plants are valued in the context of a country’s socio-economic conditions. An example is Prosopis, which was considered (using materials prepared by CABI) in 2002 in the regional consultations on the proposed first supplement to ISPM 11. This genus includes many invasive species that compete for water or take over lands when not controlled. Yet it is a useful source of fuelwood and fodder when it is managed for those purposes so countries may still choose to import Prosopis (Choge et al., 2002; Pasiecznik et al., 2001; Pasiecznik, Harris and Smith, 2004).

We have all focused on plants for planting, but in fact any organism intentionally introduced that will establish a breeding population may warrant a pest risk analysis. A species intentionally brought in for the purpose of pest control is not a quarantine species. Some intentionally introduced biological control agents, which are covered by ISPM 3, will establish a breeding population. The revision of this ISPM should address its current weakness on the risk analysis aspect for decisions regarding import and release. The scope of the draft revision has been expanded to cover intentional introductions for plant protection purposes, such as beneficial insects, soil amendments or sterile insects (Quinlan et al., 2003). It does not include plants (e.g. crops genetically modified with plant protection properties such as Bt). Thus some of the future pest risk analysis on intentional introductions other than plants may also be supported by guidance from ISPM 3. The advantage may be primarily psychological: many NPPOs already comment on the awkwardness of using pest risk analysis for “quarantine pests” on an organism that one believes is desirable and a benefit to the country. The assessment may be interpreted as more of an environmental impact analysis rather than a decision on whether a species is a quarantine pest that merits regulation.

NPPOs will need to review pathways that either are not well monitored (whether regulated or not) or are new and are known to be high risk, such as the pathway of Internet sales of plants that arrive in a country by post, generally without any regulatory review or permit.

In some instances, this first approach of expanding monitoring and regulation may require additional authorities to be granted to the NPPO. These legislative issues must be addressed to fully implement the revised ISPM 11.

Identify the most important natural systems/native plants and review all potential threats

For NPPOs with limited resources, a second approach, which may complement or replace the first one, is to work with stakeholders to decide which species or ecosystems that are not already the focus for plant protection efforts are the most important to start protecting. Usually agricultural systems are well protected. In some countries, the question of which non-agricultural systems are most valued will be answered easily.

In California, for example, ecosystems that feature oak as a keystone species have been hard hit by sudden oak death. Initially the source of this devastating damage to an important natural system was not understood. The state’s entire community, however, notes the impact. Oak species are an especially important keystone species in ecosystems in the United Kingdom as well, so when the first sign of this syndrome arose, the plant protection service (now part of the Department for Environment, Food and Rural Affairs, DEFRA) immediately began research on pathways and susceptibility of the British oak and other systems to this threat. Ornamental plants routinely imported were found to be possible pathways for the disease, now known to be caused by a fungus (Jones, Sansford and Brasier, 2003; EPPO, 2003). First the United Kingdom and now the entire European region have implemented measures to reduce the likelihood of entry of this pest. The risk management options identified by the pest risk analysis may change as new information becomes available. A review is worthwhile because the outcome is aimed at protecting a valued natural system.

This approach to implementing the revised ISPM 11 is to work backwards, cooperating with stakeholders to identify what are the most important “natural” systems or “native” plants in the country and then to review all potential biological threats to those plants or plant communities and clarify which are under the jurisdiction of the NPPO. This approach of working backwards is done to some extent with all agricultural crops because NPPOs (possibly automatically) identify the sectors with the most economic importance for the country and tend to focus efforts on those. (Witness the many countries with regulations against citrus diseases.)

While this second approach may very well identify potential pests that are the same as those targeted for agricultural purposes, the added value or weight of protecting a natural system of importance may alter the outcome of a pest risk analysis and require greater risk management. This approach may also alter the endangered area chosen for the pest risk analysis.

The approach initially may prove challenging for an NPPO that is not accustomed to consulting stakeholders (beyond perhaps a few industries) and does not have any additional funding for undertaking the pest risk analyses that will be necessary once the new species and areas of value are identified. Some pest risk analyses may be able to wait until there are applications for permission to import; others, perhaps related to pathways, may need to be undertaken as soon as possible.

This is the case for involving a broader base of interested parties, including environmental non-governmental organizations, so that information is more readily available, factors influencing the risk (e.g. non-biological threats already compromising the system or plant species) are understood, and likely pathways for entry of environmental pests are discovered. Volunteers are particularly helpful for surveillance efforts. Eradication programmes or restrictions to trade must be part of official control (refer to ISPM 5 supplement 1, Guidelines on the interpretation and application of the concept of official control for regulated pests). In some countries, exercises in preparing a national strategy on invasive alien species or similar initiatives, possibly linked with the CBD, will provide the foundation information on which species and systems most need protection.

These partnerships with domestic environmental protection authorities may support an NPPO’s aim to identify all the potential invasive species already known to exist in a country or area, and to assess the risks (with the help of ecologists), including the identification of “triggers” for invasion. This will be extremely useful in considering new import requests when limited published information is available.

Focus on particular geographic areas or areas with specific levels of protected status

A third approach is to focus efforts on particular geographic areas, such as protected areas or parks. In most countries, information on these areas will exist or they would not be protected in the first place. Both national and international experts may have conducted ecological research within the areas. This offers the advantage of baseline information and, in many countries or regions, the additional authorities of other agencies with the mandate of protecting the area.

The disadvantage is that limiting an NPPO’s efforts to one area means that the rest of the country could continue to serve as a reservoir and source of ongoing introductions of the pest in question, so that the efforts are wasted. But with limited resources, or with limited time for those areas under particular threat, this approach may be a good way to start. This will require the use of zones of pest freedom and cooperation with various agencies in the official control of a species that is already present in some parts of the country. The constant threat of re-entry to a protected area or park from the surrounding area would make this approach less cost effective, but it may be an important starting point that allows future prohibition of a species that has turned out to be a “sleeper pest” of natural areas. It may also be appropriate for countries with natural barriers that will reduce the likelihood of internal spread.

If a country begins with this approach, the NPPO will need to:

All three of these approaches to begin implementation of the revised ISPM 11 with limited resources may be employed in the course of developing an overall approach to management of invasive alien species using the authority of the NPPO under the IPPC. In all of these approaches there is a need to involve other agencies, ministries, research centres, universities, ecological societies or other organizations with existing expertise on environmental impact and invasive species issues so that this knowledge is fully accounted for in the decisions resulting from pest risk analyses and in the measures implemented under the management of NPPOs.

Pest risk analysis for pests causing indirect injury to plants

Regardless of the approach chosen to start the implementation of the revised ISPM 11, the third category of pests noted in annex 1 of the standard is likely to be the hardest to cover with a pest risk analysis. These are “secondary” pests, those that indirectly affect plants through effects on other organisms.

In 2002, during regional consultations in Thailand, Trinidad and Tanzania, CABI presented examples of pest risk analyses that might fit under the (then draft) supplement to ISPM 11. This was done to stimulate discussion and add to understanding of the concepts. NPPO participants at these meetings had a single most common concern about the supplement: they worried that an NPPO would be expected to regulate new pests and pathways for pests that were outside the experience, knowledge and training of its officials. The examples raised issues that NPPO staff normally would not know to anticipate. This is especially true for “sleeper” pests, which seem fine when first imported but become invasive after some trigger occurs. Another concern was unforeseen interactions among species.

Some of the organisms in this category of pests that indirectly affect plants through effects on other organisms may be predicted. Parasites of biological control agents or pollinators are examples. Many species of exotic ants may be in this category. For other pests, we will have to rely on ecologists to sound the warning of the potential threat before the NPPO will know to act.

Uncertainty in environmental risk analysis

The PRA framework includes uncertainty, which may be particularly important with environmental risk. Indeed, if there is no uncertainty, there is no risk: there is simply a negative impact or event. As the use of pest risk analysis expands beyond its traditional applications (e.g. to agricultural systems), it is more important than ever to properly document the uncertainty in the prediction of risk. When the uncertainty arises from natural variability in a population, for example, it may not be possible to refine the pest risk analysis. But in those instances where uncertainty arises from lack of information (e.g. about a host range), the results of new research may prompt a revision of the pest risk analysis.

NPPOs need to be able to find this information and reconsider the conclusions in pest risk analyses quickly and efficiently. They particularly need the cooperation of ecologists who are willing to reduce their findings to likely scenarios and provide a consensus of opinions. NPPOs will rely on guidance from pragmatic experts who understand the need to make decisions based on the best available information to date, while always highlighting the areas of greatest uncertainty so that new “facts” can quickly be incorporated into historic decisions.

Conclusions and recommendations

Decisions that are based on pest risk analyses are a reflection of the values of that country (see Perrings et al., 2002). With limited resources, the question is what issues will get the most attention. One of the challenges will be for NPPOs to truly reflect the values of their country, instead of remaining comfortable with their own historic interests.

Cooperation and regular communication between regulators and ecologists is particularly important on the domestic level. We hope that in the future increased interaction with ecological sciences will improve data and methodologies of pest risk analyses. We know that with environmental risks to plants now clearly incorporated into the responsibilities of NPPOs, there will be greater need for capacity building.


A grant to CABI Bioscience, United Kingdom, from the Rockefeller Brothers Fund (RBF), a private foundation, is gratefully acknowledged for supporting the production of this paper.

References and further information

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CBD. 2000. Fifth Conference of the Parties, Nairobi, Kenya, 15-26 May 2000: Decision V/6: Ecosystem approach (available at

Choge, S.K., Ngujira, F.D., Kuria, M.N., Busaka, E.A. & Muthondeki, J.K. 2002. The status and impact of Prosopis spp in Kenya. Nairobi, Kenya, Kenya Forest Research Institute. 59 pp.

Ebbels, D.L. 2003. Principles of plant health and quarantine. Wallingford, UK, CABI Publishing. x + 302 pp.

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Note: All adopted international standards for phytosanitary measures (ISPMs), listed in Appendix 1, as well as draft standards undergoing consultation, are available at

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