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Water Wise Plants
Teacher notes to accompany the Water Wise Student Work Sheet to be completed
at Alice Springs Desert Park
BEFORE YOUR VISIT
To prepare your students for a visit to the Desert Park to complete this task, you may
like to do some preliminary work on the requirements of plants, in particular their
need for water. You may then go on to discuss how plants that live in the desert
need to be very Water Wise to ensure their survival.
FACTS
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70% of Australia is arid, which means that it is hot and dry, rainfall is highly
unpredictable so you never know if or when it is going to rain.
The shortage of water available to plants is usually combined with high
daytime temperatures and low humidities, which tend to cause rapid loss of
water by evaporation.
Water intake must equal water loss if the amount of water in the plant is to
remain sufficient to support life
Despite the uncertainty of rainfall there is a rich diversity of plant life in the desert
because these plants have many strategies for collecting and conserving water.
Water is one of the most important factors triggering plant growth.
In order to survive, desert plants have developed many strategies to survive.
Desert plants can be divided into 2 major groups according to their strategy.
These are the Drought Dodgers and the Drought Tolerators
Wildflowers are the drought dodgers. They are masters of the 'boom and
bust' strategy. After the rain the seeds germinate and the plant grows, develops
and sets seed very quickly, they then die and when the next rain comes the
cycle continues. They are opportunists.
A second group of plants are drought tolerant, containing fewer species, but
making up a larger proportion of the vegetation. Many of these are Acacia
species. Acacia cope with harsh conditions by minimising the water lost to the
atmosphere through evaporation. Most plants have large leaves and small leaf
stalks that attach them to the stem. Things are the other way around on
Acacia. They have very small leaves and large, flattened leaf stalks called
phyllodes. Plants sweat through pores, just like us, the phyllodes have fewer
pores, (stomates) than leaves so they sweat less and save water. All the
leaves drop off when the plants are still very young. The phyllodes have the
same function as a leaf; they make food for the plant by photosynthesis using
sunlight, water and carbon dioxide.
During your visit to the Desert Park you will look at a number of different plants and
investigate their strategies. Most of these plants will be Drought Tolerators. This is
because we cannot guarantee a big rain followed by a wildflower bloom just prior to
your visit.
A Desert Park Guide will be able to help you plan a route around the Park, which
enables you to see the following species. The information here is in the same order as
the plants appear on the student worksheet. Students are expected to complete the
sheet, adding sketches of the leaves and the whole plant shape where required, and
information on the Water Wise strategies adopted by each plant.
You may find as you come to a plant that utilises a strategy that has been discussed
before, that students will be able to identify the strategy without being told. For this
reason after the first couple of examples it will always be worth asking the student what
they think the Water Wise strategies of this particular example are, rather than telling
them immediately.
Witchetty Bush (Acacia kempeana)
A multi-stemmed shrub growing to 4m high, the witchetty bush is well adapted to
the desert. It survives the heat by the way it’s built. The phyllodes are broad and
form a dense crown of foliage. They are covered with a waxy coating to protect
them from the sun and from losing too much water. Rather than being shaped like
trees that live in wetter areas ( with an ‘umbrella’ shaped canopy to keep the area
around the roots dry and prevent waterlogging), The witchetty bush and many
other desert plants are shaped more like funnels, catching the rain which runs
slowly down its branches to the base of the tree.
River Red Gum (Eucalyptus camaldulensis)
The River Red Gums are the very large shady trees that line the river bed. The
leaves are covered in a waxy coating to protect them from the sun. The trunks are
lightly coloured with white and grey (with some red patches) which helps them to
stay cool by reflecting the sunlight. River Red Gums also drop their branches
during drought times, which reduces their need for water.
Mulga (Acacia aneura)
Mulga is the most dominant acacia in the arid zone. It’s very small, waxy
phyllodes help it to minimise water loss. If you look closely you may be able to
see that they are aligned so that the narrow edge is towards the mid day sun, so
only a small surface is exposed to the heat. These phyllodes also point upwards
when it rains, maximising the ‘funnel effect’ to collect as much water as possible.
Mulga also has a hard rough bark which protects it from the sun and a deep root
system to capture underground water.
Desert Oak (Allocasuarina decaisneana)
Like many desert trees, Desert Oaks are very slow growing. This is because most
of the growth is going on under the ground. A 20 year old Desert Oak may be only
one metre high, but its roots would go down 10 metres under the ground. Desert
Oaks drop a lot of leaves and this makes a mulch under the tree that helps the soil
retain moisture. This carpet of needles also inhibits other trees, shrubs and grasses
growing under the tree that would compete with it for the limited water resources.
Blue Mallee (Eucalyptus gamophylla)
The bark of the blue mallee is smooth, often whitish; this waxy coating is to
protect the mallee from the harsh sun of central Australia. Their blue-green
leaves are mostly rounded and joined in pairs, encircling the stem. This leaf
structure helps to protect the branch underneath (like a wide brimmed hat) and
enables it to catch water easier, even in light showers.
Parakeelya (Calandrina balonensis)
The Parakeelya is the example of wildflowers that you are most likely to see.
Wildflowers are the drought dodgers. Drought dodgers produce large amounts
of seed as quickly as possible. Small birds such as Zebra finches, Crimson chats
and Budgerigars can eat many of these. However there are enough seeds that
have not been eaten, to produce a new crop of plants when the next heavy rains
fall. Each seed is equipped with a hard case to protect the embryonic plant inside.
They also contain germination-inhabiting chemicals to make sure the seed only
sprouts after a heavy rainfall and not after a light shower. Only a heavy fall of rain
will produce enough moisture to soak the seed and leach out these chemicals.
The seeds then quickly germinate and produce vast carpets of colour: purple
Parakeelya, pink Minuria daisies, Poached Egg daisies, yellow Billy Buttons,
Yellow Top, Wild Tomato, Pink Mulla Mulla and peas of many colours.
Spinifex (Trioda and Plectrachne species)
Spinifex grass occupies a major part of Central Australia and is a great water
saver. It rolls its leaves into hard tubes to protect to leaf surface from the hot sun.
This minimises the effects of evaporation. Their root systems are very deep to
tap into underground water and when growing on sand dunes they hold the dune
together and provide a stable footing for other plants to get established.
Bush Tomatoes (Solanum coaltilferum)
Bush tomatoes have furry leaves. The hairs on these leaves create a
microenvironment over the sweat glands (stomata), this keeps the humidity around
the leaf higher and thus reduces water loss by evaporation.
Native Fig (Ficus platypoda)
The native fig trees have very shiny leaves that reflect the sun. The leaves also
have a think waxy coating that that reduces water loss.
Native Pine (Callitrus glaucophylla)
Has small needle like leaves, which reduces the area exposed to the sun and the
area through which water loss can take place.
Concluding notes
You may like to summarise all the different Water Wise strategies that you have seen
today and then link them in to human behaviour. For example ‘unlike the plants of the
desert we are not adapted to the dry conditions, we need to protect ourselves from the
sun with hats, sunglasses and sunscreen, and we need to drink water frequently in the
heat.’
Links for further study
If you have not already connected with the Water Wise Project Officer, you may
like to talk to them about further Water Wise activities that your students can do.
[email protected]
If you wish to create a Water Wise Garden the following wiki may help
http://aridzonegardens.wikispaces.com/