A weed risk model for aquatic plants in New Zealand
The weed risk assessment model was primarily designed by the Ministry of Agriculture and Forestry (MAF) for ranking terrestrial plants, but a new model for aquatic plants has been developed. Attributes of the plant ecology, biology and weediness are assessed based on observations of their behaviour in New Zealand, and/or information from other countries. These attributes are listed below, and for each, guidance is provided about the different possible answers:
Versatility (ranked from 2 to 10, summing the different variables)
This relates to the tolerance to a range of environmental variables:
- temperature tolerance: scored from 0 to 3, 0 if the plant is killed during winter, 1 if it dies off during winter, 2 if limited by winter temperatures, 3 if frost tolerant
- salinity: 0 or 1, 0 if cannot tolerate saline conditions, 1 if can
- range of habitat: 1 to 3, 1 narrow range, 2 if able to grow from water to wetland or from shallow to deep (>5 m), 3 if able to grow from water to dry land
- water/substrate type: 1 to 2, 1 if restricted to sandy to muddy substrate, or oligotrophic to eutrophic waters, 2 if tolerant of both.
- water clarity: 0 to 1, 1 if not affected by water clarity (i.e. floating or emergent).
Habitat (ranked from 1 to 9, summing the different variables)
- lentic: rivers, streams, drains, irrigation channels: scored from 0 to 3, 0 if absent, 1 if present but not weedy, 2 if minor weed, 3 if major weed
- lotic: ponds, shallow and deep lakes: 0 to 3 as previously
- wetlands: water margins, swamp, marsh, bog: 0 to 3 as previously
Competitive ability (ranked from 0 to 10, summing the different variables)
- within growth form, i.e. submerged, floating, emergent: 0 to 8, 8 for Hydrylla, Ceratophyllum and Egeria.
- between growth form: 0 to 2, 0 if no interaction, 1 if some suppression, 2 if able to completely displace another growth form.
Propagule dispersal (ranked from 0 to 10, summing the different variables)
- dispersal outside catchment by natural agents, e.g. birds, wind dispersal: 0 to 5, 1 if propagule could be spread in bird crop, 5 if propagule is well adapted to bird/wind dispersal
- dispersal outside catchment by accidental human activity, e.g. drainage machinery, boat trailers, nets: 0 to 3, 3 if spread by the 3 methods
- dispersal outside catchment by deliberate introduction: 0 to 1, 1 if attractive to humans (ornamental fishpond or aquarium)
- effective spread within water body/catchment: 0 to 1, 1 if effective spread within water body by seed or plant fragments
Maturation (ranked from 1 to 3, summing the different variables)
Includes growth rate and time to maturity under ideal conditions.
Seeding ability (ranked from 0 to 5, summing the different variables)
- quantity: 0 to 3, 0 if nil, 1 if <100 seeds/plants, 2 if 100-1000, 3 if >1000
- viability, persistence: 0 to 2, 1 if low viability, 2 if high viability for several years
Cloning ability (ranked from 0 to 5, summing the different variables)
0 if no vegetative spread, 1 for clump forming, 3 for rhizome/stolons, 5 for far-reaching rhizomes/stolons/fragmentation capable of forming new colonies.
Obstruction (ranked from 0 to 10, summing the different variables)
- physical – water use (recreation): 0 to 2, 1 for minor nuisance, 2 for major nuisance
- physical – access: 0 to 2, as previously
- physical – water flow, power generation: 0 to 2, as previously
- physical – irrigation, flood control: 0 to 2, as previously
- aesthetic: 0 to 2, 1 for either a visual or a smell problem, 2 for both
Damage to natural areas (ranked from 0 to 10, summing the different variables)
- reduce biodiversity: 0 to 5, 5 for monospecific stands, reducing score for lessening impact
- reduce water quality: 0 to 3, 3 for major impacts especially deoxygenation
- negatively affect physical processes: 0 to 2, 2 for major effects on substrate stability, hydrology (flooding)
Other undesirable traits (ranked from 0 to 3, summing the different variables)
- health impairment, e.g. drowning, poisonous, sharp leaf edges, mosquito breeding habitat: 0 to 2, 2 for 2 or more effects
- weed of agriculture: 0 to 1, 1 if it is a weed
Extent of suitable habitat (ranked from 0 to 9, summing the different variables)
Available habitat present in New Zealand scored out of 10, amount of available habitat not occupied scored as a fraction, e.g. Alternanthera philoxeroides 4/6 (score 4), Hydrilla verticillata 9/10 (score 9)
Resistance to management (ranked from 0 to 10, summing the different variables)
- ease of implementation: 0 to 2, 2 if accessibility to weed is difficult, e.g. dense tall impenetrable growths
- recognition of problem: 0 to 1, 1 if difficult to recognize weed, e.g. submerged species
- scope of control method: 0 to 2, 1 if only one control option, 2 if no control option
- suitability: 0 to 1, 1 if control method not always acceptable, e.g. unregistered herbicide
- effectiveness: 0 to 2, 1 if partial control, 2 if ineffective
- duration of control: 0 to 2, 1 if control for 3 or more months, 2 if no control method
Problem in other countries (ranked from 0 to 5, summing the different variables)
0 if not adventive elsewhere, 1 if adventive but not weedy in tropics, 2 if a tropical weed, 3 if adventive, not weedy in other temperate countries, 4 if only a problem in some temperate countries, 5 if widespread problem weed in other temperate countries
This weed risk model has been tested using aquatic invasive plants in New Zealand. The scores obtained with this aquatic plant model have been compared to the score obtained with the MAF weed risk assessment (initially for terrestrial plants). Each species has been checked against the Global Compendium of Weeds (GCW) in order to indicate its invasive behaviour elsewhere in the world, as well as in Flora Europaea and the DAISIE Database to determine its occurrence and invasiveness within the EPPO region. This later information remains only indicative, and “/” indicates that no further information could be found.
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Species
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Origin
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Type
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Score model
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Score MAF
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GCW*
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Distribution EPPO
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Phragmites australis (Poaceae)
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Euro-med
|
Emergent, present in NZ
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74.5
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15
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W, NW, AW, EW
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Widespread
|
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Hydrilla verticillata (Hydrocharitaceae)
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Eur., Austr., India, Asia?
|
Obligate submerged
|
74
|
22
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W, SW, NW, AW, EW
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DE, GB, IE, RU
|
|
Zizania latifolia (Poaceae)
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Asia
|
Emergent, present in NZ
|
68
|
14
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W, EW
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GB, LV, RU
|
|
Ceratophyllum demersum (Ceratophyllaceae)
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Cosmop.
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Obligate submerged
|
67
|
22
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W, SW, NW, AW, EW
|
Widespread
|
|
Eichhornia crassipes (Pontederiaceae)
EPPO A2 List
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S-Am.
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Free-floating
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67
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22
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W, SW, NW, AW, EW
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ES, IT, PT
|
|
Panicum repens (Poaceae)
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Africa, Asia, Eur.
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Evaluated for import into NZ
|
66
|
9
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W, NW, AW, EW
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Widespread
|
|
Ludwigia peruviana (Onagraceae)
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S-Am.
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Evaluated for import into NZ
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65
|
13
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W, SW, NW, AW, EW
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Not recorded
|
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Egeria densa (Hydrocharitaceae)
EPPO List of IAP
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S-Am.
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Obligate submerged
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64
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23
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W, NW, AW, EW
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AT, BE, CH, DE, ES, FR, GB, IT, NL, Azores (PT), TR
|
|
Alternanthera philoxeroides (Amaranthaceae)
EPPO Alert List
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S-Am.
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Emergent, present in NZ
|
63
|
22
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W, SW, NW, AW, EW
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FR, IT
|
|
Lagarosiphon major (Hydrocharitaceae)
EPPO List of IAP
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Africa
|
Obligate submerged
|
60
|
23
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W, SW, NW, AW, EW
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BE, CH, DE, GB, FR, IE, IT
|
|
Nymphoides peltata (Menyanthaceae)
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Asia, Eur.
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Water lily
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58
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17
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W, NW, AW, EW
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Widespread, invasive in CH, DK, IE, SE
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Cabomba caroliniana (Cabombaceae)
EPPO List of IAP
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S-Am.
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Evaluated for import into NZ
|
58
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16
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W, NW, AW, EW
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BE, FR, GB, HU, NL
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|
Salvinia molesta (Salviniaceae)
EPPO Alert List
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S-Am.
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Free-floating
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57
|
17.5
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W, NW, AW, EW
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IT
|
|
Myriophyllum aquaticum (Haloragaceae)
EPPO List of IAP
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S-Am.
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Emergent, present in NZ
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56.5
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17
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W, NW, AW, EW
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DE, IE
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Sagittaria graminea (Alismataceae)
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N-Am., S-Am.
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Emergent, present in NZ
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52
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26
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W, NW, EW
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Not recorded
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Vallisneria spp. (Hydrocharitaceae)
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Subtrop.
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Obligate submerged
|
51
|
23
|
/
|
|
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Sagittaria montevidensis (Alismataceae)
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N-Am., S-Am.
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Emergent, present in NZ
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46
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25
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W, SW, NW, AW, EW
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ES
|
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Elodea canadensis (Hydrocharitaceae)
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N-Am.
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Obligate submerged
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46
|
24
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W, SW, NW, AW, EW
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Widespread
|
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Nymphoides geminata (Menyanthaceae)
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Asia, Australasia
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Water lily
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46
|
18
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W, EW
|
/
|
|
Pistia stratiotes (Araceae)
EPPO Alert List
|
S-Am.
|
Free-floating
|
42
|
20
|
W, SW, NW, AW, EW
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Canarias (ES)
|
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Regnellidium diphyllum (Marsileaceae)
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S-Am.
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Evaluated for import into NZ
|
20
|
4
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W
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Not recorded
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* Abbreviations for the Global Compendium of Weeds column:
W: weed; SW: sleeper weed; NW: noxious weed; AW: agricultural weed; EW: environmental weed.
It appears that Zizania latifolia, Ludwigia peruviana, Sagittaria graminea and Sagittaria montevidensis would deserve more attention concerning the risk they represent for the EPPO region.
Sources
Champion PD, Clayton JS (2000) Border control for potential aquatic weeds. Stage 1. Weed risk model. Science for conservation 141. Department of conservation, New Zealand. 48 p. http://www.doc.govt.nz/upload/documents/science-and-technical/sfc141.pdf
Delivering Invasive Alien Species Inventories for Europe (DAISIE) Database. http://www.europe-aliens.org/
Tutin TG, Heywood VH, Burges NA, Moore DM, Valentine DH, Walters SM and Webb DA (1964/80) Flora Europeaea, Vol 1-5. Cambridge University Press, Cambridge (GB).