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  • The Parliamentary Commissioner for the Environment report Space invaders: A review of how New Zealand manages weeds that threaten native ecosystems investigated the growing risk weeds pose to our environment to determine the scale of the problem and what is being done about it.

    The report identified a number of problems and is clear that we will never get rid of all the weeds in New Zealand. We will need to keep weeding some plants for a long time to protect the native ecosystems we value.

    Problems and possible solutions

    Identifying problems in science isn’t always enough. An important part of using science in government is to come up with ideas to fix problems based on that science or other research.

    Take a look at some of the possible solutions and work being done to tackle the problem of weeds in our environment. What solutions can you think of?

    Problem: There are 25,000 exotic plant species already in New Zealand, and hundreds of these are actively causing harm to our native ecosystems. But we don’t know exactly where these weeds are, if they are spreading, what harm they are causing and how they are managed (if they’re managed). Surveillance of weeds is patchy, and reports from the frontline often depend as much on luck as systematic surveillance.

    Solution: Improve monitoring and surveillance of weeds. This could include improving existing weed information systems to provide everyone managing weeds with a single authoritative and publicly accessible database of all exotic plants in New Zealand. This would help by making sure we use the same name for each weed (some are known by many names) and knowing where exactly the weeds are and the best way to remove them.

    Problem: We can’t get rid of every weed in the country – there are simply too many – but currently not enough is being done to prevent exotic plants from escaping from the gardens into the wild or to adequately address the risks from the plants that have already escaped (the plants that have ‘jumped the garden fence’).

    Solution: Work with scientists to prioritise which weeds are the most important to tackle. This could also include establishing an expert team to scan for emerging risks from new exotic plants that may be tomorrow’s weeds and help manage them. This will help nip a new invader in the bud and save a lot of money and hard slog in the long run.

    This prioritisation will be based on science relating to the risk each weed poses to native ecosystems. These risks include:

    • how likely a weed is to invade a given location
    • how well established or spread the weed is in a given location
    • the degree of harm it can cause to ecosystems once there
    • the potential for further spread (how far along the invasion curve)
    • what will happen once a weed has been removed has to also be considered (removing weeds can create “weed-shaped holes” where an empty space from removing one weed can become fertile ground for other weeds to move in).

    Most of these risks are determined by the physical attributes of the plant – such as how the plant reproduces and how it can be dispersed.

    Problem: Weed management is done by a large variety of different groups – the Ministry for Primary Industries manages the biosecurity system, the Department of Conservation manages weeds on government land like reserves and national parks, local government manages weeds on local government land and sets local rules, and landowners and community groups tackle weeds on their properties and in their neighbourhoods.

    But not all groups are focused on the same weeds or are communicating about the problems. Weeds don’t respect property boundaries, and if not managed in some areas, they can continue to provide a constant source of seeds to the surrounding area.

    Solution: Help align national, regional and local weed management efforts so all groups are working effectively together. This means figuring out which weeds to tackle, how each weed should be managed and who is working where.

    Community conservation

    Defeating weeds will not be achieved by top-down policies alone. Much of the weed control happening every day throughout the country is being done by passionate community groups, iwi, hapū and landowners.

    Rt Hon Simon Upton, Parliamentary Commissioner for the Environment

    Central and local government are required to manage weeds that harm native ecosystems across the country – but they are not the only ones weeding!

    Aotearoa is fortunate to have large numbers of passionate individuals, landowners, kaitiaki, hapū, iwi and community groups willing to devote their time and effort to protecting native species and biodiversity. For Māori, there is often an additional layer of management framed by te ao Māori that emphasises connection to the land, multi-generational thinking and considering the needs of Papatūānuku first and foremost.

    One study estimates there are at least 600 community environmental groups restoring degraded sites. Most of these restoration efforts require some control of weeds and planting of natives.

    The report profiles five community groups from Stewart Island/Rakiura to Northland to showcase community and individual action against weeds and some of the challenges these groups face. One case study (from page 201 of the report) looks at the work of rongoā practitioner Rob McGowan.

    Taking action is a valuable addition for science learning. Action taking as part of an inquiry model can provide opportunities for students to develop valuable skills. Action taking provides students with a sense of hope, they are empowered to make a difference and this is linked to wellbeing. Learn about ways in which students and schools can take action for conservation in this recorded PLD webinar. Find a local conservation group here.

    Related content

    Weeds and native ecosystems – a context for learning provides curriculum and pedagogical ideas for exploring this vexing topic.

    The article Weeds – threats to native ecosystems has additional information about the exotic weed problem in Aotearoa.

    Watch the video Pest plants to see some of the key pest plants around the Waikato River.

    Use the Connected article The war on weeds to find out how students at Kaniere School are helping scientists combat the spread of weeds using simple digital technology and the citizen science database iNaturalist.

    Learn about a biocontrol tool used to control a pest plant in Weevils eat pesky buddleia weeds.

    Activity ideas

    In the activity Threats to biodiversity, students research three aspects of biodiversity loss – direct species loss, habitat loss and pests and weeds.

    Use the activity Plant reproduction – literacy and numeracy learning links to record and deepen student understanding of key science ideas.

    Useful links

    Download the Parliamentary Commissioner for the Environment Space invaders report and related publications, including Rob McGowan’s consultant report Mauri tū! Mauri ora! Māori perspectives on exotic plants in Aotearoa here.

    Read more about some of the community organisations from the Space invaders report – Project De-Vine Environmental Trust (Golden Bay and top of the South Island), Stewart Island/Rakiura Community & Environment Trust (SIRCET) and their ‘war on weeds’ project and Weed Action Native Habitat Restoration Trust (Whangārei).

    This New Zealand Geographic article Jungle warfare looks at pest plant species and how people are taking action.


    This resource has been created from Space invaders: A review of how New Zealand manages weeds that threaten native ecosystems and associated resources (including this FAQ) with support from the office of the Parliamentary Commissioner for the Environment.

      Published 7 June 2023 Referencing Hub articles
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