Tuesday, 26 May 2020

Autumn Leaf Study in New Zealand - leaf art, leaf scavenger hunts and more

Autumn around the world is a time that lends itself to investigate leaves, through making leaf art, going on a leaf scavenger hunt and learning about trees and their leaves.

Yet in New Zealand where almost every native tree is evergreen, the emphasis on trees changing colour and losing they leaves could seem to favour introduced trees over native trees. Here are some activities and ideas for studying native tree leaves in New Zealand. Autumn is still a good time to study leaves as it is interesting to compare deciduous and evergreen trees.

ACTIVITY: Go on a leaf hunt to find different colour leaves and identify whether trees are evergreen or deciduous. 

Deciduous trees - those that lose their leaves in autumn - do so to survive a cold winter, saving energy and getting rid of leaves that might pick up diseases. The trees draw back into their branches and trunk all the goodness that was in the leaves, such as water, nutrients and the green substance chlorophyll. So the leaves change colour, dry out and fall.

There are some parts of New Zealand where many deciduous introduced trees have been planted. Even in a warmer climate they continue to loose their leaves in autumn.
Autumn leaves of deciduous trees in Nelson, New Zealand
Generally it isn't cold enough in New Zealand for our native trees to have adopted this method of survival. Instead, evergreen trees lose a few leaves all year round - discarding old leaves and making new ones. Here's a collection of pōhutukawa leaves I picked up in my garden. The discarded leaves show just as much of an array of different colours as the autumn deciduous leaves, and all while the tree itself is covered in green leaves. So don't be tricked by the colour of the leaves on the ground, check to see whether all the leaves on the tree are changing colour.
Pōhutukawa leaf collection - despite the range of colours found, pōhutkawa is
not a deciduous tree, always look up into the tree itself to see whether the leaves
are all changing colour
ACTIVITY: hunt for a leaf skeleton

Dead leaves form leaf litter on the forest floor. Eventually these leaves rot and breakdown along with other plant matter to form soil. The last part to rot is often the vein structure.
Leaf litter under mahoe and kohekohe trees
In skeleton leaves, the leaf's structure of veins is really obvious.
The fine detail of a skeleton leaf

ACTIVITY: Making Leaf Art - clay impressions, leaf rubbings, leaf prints

If you look closely you'll see how different trees have quite different arrangements of veins in their leaves. Veins carry food and water back and forth. The green substance in leaves - chlorophyll - turns the sun's energy into food. The tree also gets nutrients and water from the ground some of which would go to the leaves.

Some leaves have very clear veins,
 sunshine through a pukanui leaf highlights the vein structure
This structure also means you can make interesting art out of leaves!
Leaf impressions in clay used to create pottery bowls and plates
Leaf impressions can be used to decorate clay or even cookie dough (to be safe use leaves that are edible if making impressions in something that will be eaten).
Leaf rubbings in a nature journal, the pencil colours match the colour of the leaves
To make leaf rubbings, choose leaves that lie flat and which have clearly defined veins. Put the leaf under the paper so that its underside faces upwards. Start by carefully rubbing a crayon or a coloured pencil along the outline of the leaf and then, keeping the leaf in one place, move inwards until the whole leaf has been covered.
Rangiora leaf print

Kawakawa leaf print
To create leaf prints, cover the underside of the leaf with paint, and then press it down onto the paper. Experiment with different paper, some is more absorbent than others and also with different amounts of paint.

ACTIVITY: Go on a leaf scavenger hunt to find leaves of different shapes and textures 

Did you know?
Did you know tough leaves of mutton bird scrub were used to write letters or postcards and mailed from Ulva Island in Rakiura/ Stewart Island? The ferry to Ulva Island still uses these leaves as tickets today. The underside of the leaf is soft and white, making a perfect writing surface.
Reusable ferry tickets (and compostable when they get too worn out)
Rangiora is related to mutton bird scrub. It has a similar white underside, and is a softer leaf. It is found around other parts of New Zealand, and is often jokingly called 'bush toilet paper'. You could also use its underside for writing messages.
Rangiora leaves have many uses but they are poisonous
The Meaning of Trees by Robert Vennell has interesting information about what different leaves have been used for over the years, such as medicines, tea, for making toys, for weaving. This book is a good place to check whether trees/leaves are poisonous.

Trees and shrubs that live by the sea, such as mutton bird scrub and pohutukawa, often have tough or shiny leaves to enable them to survive the salt spray and strong winds. Another common example is taupata.
Taupata can survive salt winds
Some trees have leaves that are made up of several leaf blades grouped together, the general name for this is compound leaves. When they look a bit like fingers, the name for this is palmate. An example, is five finger, here all five leaf blades count as one leaf.

Five finger or whauwhaupaku
Another tree with compound leaves, is kowhai, in this case the leaf blades are grouped lengthwise and are called pinnate
Some trees have leaves that are not all the same shape, young horoeka /lancewood trees have one shape leaf and as they get older the leaves change. Occasionally you can see both types of leaf on the same tree.

Kotukutuku, native tree fuchsia is one of the few native trees that is deciduous.
Trampers walk through bare kotuktuku trees in the spring
Kotukutuku flowers and leaves

More information about trees and native plants:
On Science Learn for schools
On NZ Plant Conservation Network clear training module on plant ID
iNaturalist for identification of your observations

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