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Analysis of environmental risks: How to assess and manage risks of invasive alien species harmful to plants? Gritta Schrader Federal Biological Research Centre for Agriculture and Forestry, Department for Plant Health Invasive alien species A species, subspecies or lower taxon,

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Analysis of environmental risks:

How to assess and manage risks of invasive alien species harmful to plants?

Gritta Schrader Federal Biological Research Centre for Agriculture and Forestry, Department for Plant Health

Invasive alien species

A species, subspecies or lower taxon,


outside its natural past or present distribution

whose introduction and/or spread

threatens biological diversity

(according to the Guiding Principles on invasive alien species, CBD)

Examples for IAS in the context of plant health
  • Horticultural pests (e.g. Phytophthora ramorum)
  • forest pests (e.g. Ceratocystis fagacearum on oaks; Bursaphelenchus xylophilus on conifers)
  • Indirect pests (bee parasites, e.g. Varroa jacobsoni; earthworm predators, e.g. Arthurdendyus triangulatus)
  • Plants (weeds, invasive plants e.g. Kudzu, Lysichiton)
Plants as plant pests

Invasive alien plants can pose serious threats to

cultivated and wild plants

 this provides the chance to regulate them as

„plant pests“

within the framework of the plant health regulatory systems

IPPC and EPPO have adopted statements accordingly

Not all alien plants have to be managed

There are many desirable alien plants, embellishing parks, gardens, and landscapes. Only very few cause problems, but these problems can be massive

Tens Rule:

10 % of introduced species spread, 10 % of these establish, and 10 % of the established species cause problems (= 0,1%)

 PRA is important to identify these few species!

„pest plant“

Invasive alien plants in plant quarantine

Basic requirements(according to ISPM No. 11):

  • plant has to fulfil definition of a pest of plants,
  • criteria have to be clearly documented, consistent and transparent,
  • if invasiveness is suspected, a certain evidence has to be demonstrated
Guidance on PRA: Standards by IPPC and EPPO

Prevention of introduction of invasive alien species harmful to plants or selection of adequate control strategies

if introduction could not be prevented

  • International Standard on Phytosanitary Measures ISPM No. 11 (2004):

Pest risk analysis for quarantine pests including analysis of environmental risks and living modified organisms

  • EPPO Standards PM 5/3(1) and PM 5/4(1):

Revision: PM 5/.. (2) Guidelines on Pest Risk Analysis;Decision-support scheme for quarantine pests (approved by EPPO working party in June 2005)

PRA: Differences in the assessment of plants
  • invasive plants have effects on ecosystems, habitats or species, impacts are generally described in qualitative rather than in quantitative terms
  • unintentional introduction: seeds or other propagules contaminating imported commodities
  • intentional introduction: plants for planting, for agricultural, horticultural or landscaping purposes
  • differentiation intended/unintended habitat
  • from a traditional pest, you know before that it is able to cause damage - from a plant often not
Unintentional introductions
  • introduced unintentionally into a country as e.g. contaminants of seeds, bird seed, oil seed, grain, fodder, wool, soil or other growing medium, or of vehicles, machines or containers
  • Relevant pathways for weeds/ invasive plants to be considered and the associated risk to be estimated
  • no intended habitat
Intentional introductions
  • movement of the plant into a country and subsequently into a certain area is intended
  • very important to consider pathway(s) from intended habitatto unintended habitat
  • often promoted, that the plant establishes in the intended habitat
  • escape into unintended habitat may cause severe problems...
Assessment of (potential) invasiveness
  • Is the species invasive elsewhere?
  • Is it highly adaptable to different environments?
  • Does it have a broad ecological amplitude?
  • Does it have a high reproduction rate?
  • Are propagules highly mobile?
  • Does it build up persistent seedbanks?
  • Is it highly competitive?
  • Does it benefit from cultivation, browsing pressure etc.?
More information on (potential) invasiveness
  • experimental plantings (but time-lag effect difficult to be assessed)
  • surveillance after planting
  • reports from other area(s) that species starts to spread
  • intended use of a plant species to be taken into account
  • volume and frequency of introduction of the plant into new areas
  • invasibility of relevant (intended/unintended) habitats
Invasibility of relevant habitats

The success of a plant in invading a certain area will also depend on the invasibility of the relevant habitats, so this will have also to be assessed

  • sites modified by man
  • strongly disturbed grounds
  • nutrient rich / poor soils (or waters)
  • vegetation close to nature
  • ...


Case study: Lysichiton americanus
  • intentional introduction, easily available (garden centres, internet)
  • pathway intended - unintended habitat: intentional planting
  • biotic and abiotic factors favorable for establishment in PRA area
  • in some parts of PRA area already established and invasive
  • broad climatic amplitude (native area: California to Alaska)
  • high reproduction rate
Case study: Lysichiton americanus
  • propagules highly mobile (moving long distances by water, soil, attached to machinery)
  • seeds viable in soil for at least 6 years
  • highly competitive (large leaves build dense layer)
  • reports from other areas about spread
  • swamp woods highly invasible (vegetation close to nature)
Difficulties of predicting invasiveness
  • certain attributes increase likelihood of invasion, but are not in any case necessary for invasion success
  • plant may have all these attributes without causing any problems
  • no known broad scientific criteria for all (potentially) invasive plants in all relevant circumstances
  • complexity of ecosystems
  • variability associated with organisms, habitats, environmental factors
  • lack of data
Consequences of establishment and spread

Direct effects or primary consequences include:

  • Reduction of the abundance of keystone plant species
  • Reduction of plant species that are major components of ecosystems
  • Reduction of endangered native plant species
  • protection of other plant species against significantreduction, displacement or elimination

Endangered species receive more attention than just normalspecies because of their status

Reduction of keystone species

Important keystone species in European forests: Pinus sylvestris

  • can play a critical role in forest biocenosis
  • has relationships with many plants and animals
  • affects resource availability
  • is very susceptible to the pinewoodnematode Bursaphelenchus xylophilus
Consequences of establishment and spread

Indirect effects or secondary consequences include:

  • significant effects on plant communities (species richness, biodiversity)
  • significant effects on designated environmentally sensitive areas
  • significant change in ecological processes and ecosystems (includingfurther effects on plant species)
Consequences of establishment and spread

Indirect effectsor secondary consequences include:

  • effects on man's use (e.g. tourism, hunting, fishing)
  • costs of environmental restoration
  • effects on human and animal health (e.g. toxicity, allergenicity)
  • effects of eradication, control or other management measures
Assessment of economic consequences

Consideration of "use" and "non-use" values

"Use" values:

consumptive (e.g. fishing)

non-consumptive (e.g. using forests for leisure activities)

Assessment of economic consequences

Consideration of "use" and "non-use" values

"Non-use" values:

  • option value (value for use at a later date)
  • existence value (knowledge that an element of the environment exists)
  • bequest value (knowledge that an element of the environment is available for future generations)
Case study: Lysichiton americanus

Primary and secondary consequences

  • significant reduction of endangered and other species (rare mosses, orchid-species)
  • effects on plant communities and designated environmentally sensitive areas (swamp woods are rare habitats)
  • change in ecological processes and the structure of ecosystems, as huge leaves build a dense layer excluding light
  • use and non-use values affected: non-consumptive, option, existence and bequest values
Management of (potentially) invasive alien plants
  • raising of public awareness
  • surveillance after planting
  • preparation of control or emergency plans
  • restrictions or codes of conduct on import, sale, holding, planting
  • notification before import
  • restrictions on movement
  • obligation to report findings
Management of (potentially) invasive alien plants

raising of public awareness

  • explanation / illustration of risks
  • recommendations what to plant instead
  • recommendations to eliminate invasive plants
  • information of road maintenance departments etc.
  • information of garden centres
Management of (potentially) invasive alien plants

restrictions or codes of conduct on import, sale, holding, planting, or movement…

  • required growing conditions
  • authorisation of habitats
  • prohibition to plant into or move to
    • nature conservancy areas
    • areas otherwise protected
    • areas where not yet widely spread
    • areas where under official control
Case study: Lysichiton americanus

Trade, introduction and movement of L. americanus have negative, irreversible environmental impacts. Without strict prevention, more invasions are foreseeable. Proposed measures/requirements:

  • increase public awareness of the risk posed by this plant
  • prohibition or restriction of import, sale, holding, planting
  • restrictions on/conditions for planting
  • prohibition of movement
  • obligations to report findings
  • monitoring/surveillance
  • emergency plan
  • establishment of an action plan for local eradication when the plant is found
  • Determination whether a plant is (potentially) invasive: How to do an effective pre-screening?
  • How to avoid unnecessary or unbalanced trade restrictions?
  • Thresholds for damage?
  • Increase experience
  • Collection and sharing of data, databases
  • Diagnostic and taxonomic networks
  • How to deal with the work load?

PRA is a useful tool for the assessment of risks posed by invasive alien species harmful to plants. IPPC and EPPO standards are available for this purpose.

The experience for their application and implementation in particular with regard to plants as pests has yet to be increased. Abstraction from ‘traditional pests’.

PRA on environmental risks is difficult due to high levels of complexity in ecosystems, uncertainty about threats to biodiversity, pressure arising from globalisation etc.

PRAs including management options could provide the basis for WTO recognised regulation of specified invasive alien plants, including prohibition or authorisation of import, conditions for introduction or use etc.