How and why were weeds introduced and spread?

Learning Outcomes:

• Students can give reasons about how and why weeds were, and still are being, introduced into New Zealand .
  
• Students can describe the different ways weeds are spread and suggest methods of how we can help reduce weed dispersal.

Resources Required:

1. The Tale of Old Man Gorse
2. World Map
3. Pest Plant Fact Sheets from DOC or regional council
4. Weedy Web Guide 2
5. Weedbuster Investigation

Activities:

1. Read the story 'The Tale of Old Man Gorse'. In groups investigate the how and why of weed introduction. Use the Pest Plant Fact Sheets and a world map to chart the introduction of some common invasive weeds! Be sure to include the reason behind why each weed was introduced e.g. privet was introduced from China as an ornamental and hedging plant. Make a class wall display with your findings.

2. Investigate how weeds are spread using the Landcare Research website!

   Answer the questions on Weedy Web Guide 2, as you navigate through the site. You may like to work in small groups. Discuss as a class and add any new ideas to your Pool of Knowledge.

3. Conduct investigations into seed transport! Use the 'Weedbuster Investigation' to look at how humans and livestock can transport seeds. (note: socks simulate the hairy feet of livestock (sheep, cattle etc) that transport seeds while an additional investigation into how cars can carry seeds shows how humans can transport seeds too!) Go on to create your own investigation.

4. Design a poster that shows the ways in which humans spread weeds around. Suggest how we can help to halt the spread of weeds, for example, by taking garden rubbish to the dump.

5. Getting Creative! Use your knowledge gained in the previous activities to create a story, poem or cartoon strip that shows how a particular weed has come to New Zealand and how it has spread around. Share your learning with your class - you may be able to turn someone's creative ideas into a class play!

Extra Activities:

Why do weeds do so well in New Zealand ? Investigate the climate and terrain of the countries where some of our weeds originally came from. Are there similarities between our countries that could suggest why they like it here?

Why are they not a problem in their home country? See www.landcareresearch.co.nz - 'Why do some weeds grow better than native plants?'

Put yourself into the shoes of an international traveller who has visited a farm in England and has bought his/her gumboots back home! What would you have to consider when bringing your gummies home? Go to the school section at www.protectnz.co.nz and check out the 'New Wicked Biosecurity Website' link made just for kids! Design a pamphlet or brochure to inform other people about what to do when you arrive back in New Zealand from an overseas trip!

Reflection:

How have weeds been introduced into New Zealand ?

How could you and your family help to stop the spread of weeds?

Add any new ideas to your Pool of Knowledge.

Teachers' Notes:

Weeds have been introduced into New Zealand in a variety of ways.

Historically, settlers coming to New Zealand missed the familiar plants of home so they brought some with them for crops, food for livestock (e.g. wheat and barley) and for their gardens (e.g. gorse, woolly nightshade and privet).

The large movement of troops and equipment during World War II also accounts for weed introduction.

More recently weeds have been introduced for agriculture (pasture grasses) forestry (pine trees) and horticulture (kiwifruit). Many people grow plants in their gardens that are from other countries because they are pretty while over half of New Zealand 's aquatic weeds were introduced as ornamental plants for fish tanks!

Seeds are spread into new areas in four main ways;

Wind - some seeds have a shape adapted for being carried in the wind e.g. pampas seeds are like feathers).

Water - seeds and fragments of stems from plants living close to waterways are transported by rivers and streams to new areas e.g. wandering jew.

Animals - animals such as birds and lizards eat the fruit of weeds and fly/run off with the seeds inside their gut. Eventually the seeds are passed out of the gut unharmed in the animal's poo! E.g. wild kiwifruit and woolly nightshade.

The plant itself - some plants have seed pods or seed heads that burst open, dispersing the seeds into the environment e.g. gorse and moth plant pods.

Weeds can also be spread by vegetative dispersal where stems break off and re-root where they land e.g. wandering jew, or some have long roots or runners that can produce shoots from the mature plant e.g. blackberry, kiwifruit.

Humans are also responsible for weed transport by dumping garden rubbish on roadsides and in the bush, selling weeds in nurseries, dumping fish tank plants into local waterways, picking up weeds or part of plants on vehicles and boats and by trampers carrying seeds in their boots.

Source: Landcare Research website

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