Weed risk assessment

NIWA has developed a model to assess the potential weed risk of aquatic plants.

NIWA has developed a model to assess the potential weed risk of aquatic plants.

The key variables evaluated in the model are:

  • invasiveness (the ability to establish and displace other plants)
  • potential geographic distribution
  • extent of potential impacts.

Invasive attributes include habitat versatility (sensitivity to temperature, salinity, substrate, flow and water depth), competitive ability compared with other species, and effective dispersal measured as a combination of reproductive output and mechanisms of spread. Potential distribution depends on availability of suitable habitat. Impacts include damage to natural ecosystems, changes to biodiversity, obstruction of water uses, and resistance to management activities.

Reports and papers

Applying the Model

The Aquatic Weed Risk Assessment Model (AWRAM) provides a robust and scientifically defensible decision support tool for managers. The Ministry for Primary Industries (formerly MAF) have used the results obtained for various weedy aquatic plants using AWRAM in their process to decide which species are managed under the Biosecurity Act. These include:

  • Determining species prohibited entry into New Zealand, with eleven species not known to be present in New Zealand classified as Notifiable Organisms

More information on Notifiable Organisms 

  • Determining species that are managed nationally in eradication programmes under the National Interest Pest Response (NIPR) programme, with six aquatic species managed in this way

More information on the NIPR programme 

  • Banning the propagation, sale and distribution of ornamental pond and aquarium plants under the National Pest Plant Accord (NPPA) with 30 aquatic plants currently managed

Find out more about the NPPA 

These management actions assist New Zealand's biosecurity system by keeping risks offshore, prevents future impacts of high risk species and reduces the volume of plant propagules being spread around New Zealand. 

A diver adjacent to a dense weed bed of Ceratophyllum demersum. Credit: Rohan Wells