Thursday, June 26, 2008

Sex and the Cassowary Trees

Casuarina and Allocasuarina species
I noticed my first casuarinas of the season in flower this week.

Strictly speaking, the above photo doesn't belong on this blogsite, whose subject is plants of our local basalt soils, as this red flower is on a  thready-barked she-oak, Allocasuarina inophloia a lovely shaggy-barked species found on granite soil at Crows Nest. The female trees were decked out with their tiny red flowers, waiting for the wind to blow pollen across to them from the brown catkin-like flowers on the nearby “he-oaks”.

It is the time to be on the lookout for the flowers of all our local species.
I checked my forest she-oaks (Allocasuarina torulosa) when I got home, and found that I had missed the flowering (they tend to be an early species), and the little seed capsules were already forming. All four of them have turned out to be females, fertilised by males on (developer-owned) nearby bushland.
As our suburbs spread out and take over the bush, our forest she-oaks are disappearing. Some of them, I have discovered, fall victim to people who are unaware that there are different species of Casuarina, and mistake our very inoffensive, modest-sized locals for some more aggressive species. (Casuarina glauca is a plant native to coastal catchments. It doesn't belong on the Darling Downs, and is proving to be distressingly invasive, with very difficult-to-control suckers, where it has been planted.)

Casuarinas of all kinds are favourite trees of mine, with their “cassowary-feather” branchlets that catch the wind and sing.

Best of all, to my mind, are the forest she-oaks, with their fine weeping foliage that is red in the springtime (mine are just beginning to show red now), and their corky, fissured trunks (pictured at right). The exaggerated ridges of these twenty-year-old trees will modify with time but the trunks are always pretty.

Saturday, June 21, 2008

Mountain Coolibah

Eucalyptus orgadophila
This is a handsome tree of the fertile basalt hillside soils to the west of the dividing range, and is common in the outskirts of Toowoomba. It prefers a neutral pH, and a good proportion of phosphorus. Where it occurs naturally it is an indicator that these conditions occur. There are some Australian plants which really don’t like phosphorus at all – so the natural occurrence of Mountain Coolibah may tell you that Banksias and Grevilleas, for example, just won’t do well in your garden.
Mountain coolibahs are “half-barks, whose grey fibrous bark persists on the lower trunk. The beautiful smooth pale grey branches shed their bark every spring.
They are outstanding trees for wildlife. Koalas love the leaves. Old trees make good hollows (see article below), which are safe havens for gliders and other shy bush creatures. And it's a good honey tree, flowering in late winter.
Our most drought-hardy orchid, the beautiful black orchid of the west (Cymbidium canaliculatum) survives drought by sending its great mass of roots deep into its cool hollows - sometimes as far as 10 metres!
These are middle-sized eucalypts, still too large for our closer suburbs, but very suitable for small acreage gardens, and are drought and frost hardy.
In our original mountain coolibah woodlands, kangaroo grass Themeda triandra, which is now so fashionable for landscape gardening in the cities, was the dominant grass. Overgrazing has caused it to be supplanted by other grasses on our farms, but planting kangaroo grass with this tree in a garden setting would be a nice touch. Its bird attracting seeds would add to the wildlife appeal of your coolibah corner.

Hollows for Wildlife

I was told an interesting “tree-fact” recently - that mountain coolibahs (Eucalyptus orgadophila) form hollows younger than most trees.
This is a matter of great interest to much of our wildlife. 17% of Australian bird species need hollows to breed. 42% of our native mammals cannot survive without them to shelter in. 28% of reptiles need them. So do tree frogs, and bees, both native and introduced. And our most drought-hardy orchid, the black orchid Cymbidium canaliculatum could not exist in the wild without them.
The hollows they will use range in size from ones with openings from 2cm to 75cm diameter, and useful depths might be anywhere from 10cm to 10m.
We modern Australians have been very hard on our hollow trees. Clearing them has been seen as part of good forest management, and, on a smaller scale, as good housekeeping. There is good reason to clear them, of course, where a weakened tree might fall on a roof, but it’s a pity to see them disappearing on the “acreage allotments” which are expanding the borders of our suburbs so far into the bush. Their perceived untidiness counts against them.
Yet even dead trees should be retained where possible because of their high habitat value. Some of our wildlife actually prefer them to live ones, and they can be statuesque and beautiful things, deserving of a place in a garden. A good many gardeners who have no naturally-occurring dead trees seem to wish they had them, as they choose to enhance their landscaping by careful placing of interesting and good-looking stumps which they have collected from somewhere in the bush. How much luckier are those who have naturally occurring dead trees on their places!
A healthy environment has about 30 hollows per hectare. It would be possible to reproduce these conditions in our suburbs by retaining existing trees with natural hollows, and by supplementing them with sturdy, well-designed nestboxes. Each species has very specific requirements about shape and size, so variety is important.
We can also think about planting for the future.
It is true that even something like a mountain coolibah is unlikely to form hollows for its first seventy years of life, and most other trees take from 120 to 300 years to do it - but good gardening is not just about short-term results, after all.
Here is a list of particularly good hollow producing local species: Angophoras, Eucalyptus albens, E. moluccana, E. camaldulensis, E. melliodora, E. microcarpa, E. orgadophila, E. populnea, E. saligna, E. tereticornis, E. viminalis, and Lophostemon confertus.
Rainforest and scrub species also make valuable hollows, and cater for a different range of wildlife. Some good ones are: Castanospermum australe, Flindersia species, Gmelina leichhardtii, Siphonodon australe and Ficus species of the strangling type.

Friday, June 13, 2008

Irongate Environmental Reserve

I visited this reserve, which is between Pittsworth and Mt Tyson, last week and was delighted with the mee-meei (Pittosporum angustifolium/phylliraeoides) which were heavily in fruit.
The mee-meei at this site are the best of any I’ve seen, with large brilliantly coloured capsules, the colour of a really good ripe apricot, both inside and out. They were just beginning to open and reveal the deep red, sticky seeds inside. Do click on the photo for a really good look at its lovely details.
Irongate reserve is a good example of the dry rainforest / vine scrub vegetation typical of the black soil slopes west of the dividing range. Many of the plants are labelled, and they include the native ebony, (Diospyros humilis).

There was also a good population of the heavy vine called gargaloo (Parsonsia eucalyptophylla), which would make the reserve well worth a visit in summer when this plant is in flower. It is the showiest of the Parsonsias, having masses of highly perfumed white flowers. The insects which they attract - and the birds which THEY attract - are something else to attract us to this valuable reserve.
I love the beautiful trunks on old specimens. (Photo below)

Here it is growing on the stump of an old, dead bumble tree (Capparis mitchellii).
Mature bumble trees with their large edible fruits that smell like rotten oranges when ripe, are also common in the reserve and attract clouds of butterflies in spring and summer.

Also worth seeing are the Hovea longipes, which are common there. This species is a much more substantial woody shrub than we usually expect a Hovea to be. It produces its deep purple pea-flowers sometime between August and October, and is a good ornamental species to grow in blacksoil gardens.

Irongate Reserve is remarkably weed-free.
We need to protect our relatively uninvaded bits of bush - not just because they are the areas that give our native plants the best chance, but because they are reasonably easy to restore to their pristine state. Far better to begin caring for these areas when infestation is sparse, than to wait until they get to a state where a “friends” group has to spend enormous long hours on what, in many of our local “bushland” areas, may well be a hopeless task.
I was sorry to see a few plants of the horrible introduced blackthorn there. It’s such a nasty weed.
There was also a small amount of mother-of-millions. Our little group weeded out the bits we saw, which was an easy, one-plastic-bag sized task. No doubt more will come up from seed, though. If you go there, could you carry a plastic bag with you and spend five minutes doing the same?
Go to Mt Tyson, and head west out the main street. Near the property called Adora Downs the road makes a right-angled turn to the left (south). Follow this until it hits a T-intersection. Turn left, and in about 200 metres you see the Irongate Hall on the left. Turn right (south) almost immediately after that, and follow the road )which makes a bend to the left) for something like 3.5k until you come across the reserve on your right. Keep your eye out for the iron gate that marks the place.

Three Hundred Year Old Ebony Tree

Diospyros humilis (D. ferraea subsp humilis)
The most interesting plant I saw this week was a native ebony, pictured at left, at Mt. Tyson.
It’s estimated age is three hundred years. It’s a good example of the size-for-age typical of our local dry rainforest/vine scrub tree species. Relatively small when mature, they are well suited to suburban planting. We can have our trees, confident in the knowledge that we won’t find ourselves with a future monster in need of expensive removal.
There are four local species of ebony, all potentially good garden specimens. As with many rainforest tree genera, they have one species which is better adapted to dryness, and this is it. (Photo at right is another specimen in Irongate Environmental Park.)
It’s a slow-growing tree, the smallest native ebony and its well-formed canopy and deep green, shiny leaves, (red when new), make it pretty at every stage of its life - the perfect thing to pop into the garden among faster-growing but perhaps shorter-lived plants. Its deep roots mean that it lives in harmony with close neighbours, neither suffering from competition nor causing others to suffer, and needing no care at all once it has passed the baby stage.
Typically of dry-adapted plants, it has the littlest leaves of all the ebonies and may lose them in dry weather. A bit of help from a gardener in the form of mulch and perhaps supplementary watering will help keep the canopy dense all year round.
The little acorn -like fruits are produced in generous quantities. They are edible, but at that size are hardly worth the trouble. They are best left for the birds, which love them.
The heartwood is black. This is one of the best ebony timbers - another good reason for putting some of these trees for future generations to enjoy.

Thursday, June 5, 2008

Floating Ferns

Azolla species
There’s nothing like a bit of rain to cheer us up, is there?
A plant which is pure delight after rain is the little floating fern, Azolla filiculoides. Each frond carries a drop on its waterproof back, as if it’s holding it up for us to examine, saying, as a cat does with a mouse, “see, look what a precious thing I have caught!”
As children, my brothers, cousins, and I were fascinated by the expression “cats always land on their feet”. Being scientifically inclined, we tested the aphorism with the help of my cousins’ very patient ginger mog, and established its truth to our satisfaction. Old Pickles allowed us to drop him, upside down, three times before deciding that his interests lay elsewhere. Being kindly and considerate children, we had been careful to drop him from a good height to give him time to turn over. We performed the experiment by standing on a bed and dangling him by his legs over the floor, before letting go.
A similar trick can be done for the edification of children, and without incurring disapproval from those who think that dropping cats, from whatever height, is not the way to treat the family pets. Azolla ferns have water repellent backs. If you push them, upside down, under the water, they always float to the surface, triumphantly right-side up and dry.
Each plant consists of a single frond not much more than a centimetre long, with roots on the underside. In the shade they are green, but sunshine brings out the pink in them. They are annuals. No individual plant lives for longer than a season. They reproduce by division - an unusual method among plants.
Our two locals are members of widespread species, native to Australia and elsewhere.
Pacific Azolla, Azolla filiculoides (above) grows best in winter.
“Filiculoides” means “like little threads”, and each plant of this species has a generous bunch of threadlike roots which you can see below the water in the top picture. (Click on it for a close-up look. Note that each root is a SINGLE thread, like a strand of sewing thread - no little fluffy side branches.) It is the less vigorous of the two local Azolla species, and is a delight in a garden pond, ornamenting the water’s surface with pretty dapples of coral pink and green.

Ferny Azolla Azolla pinnata (below, both pictures) has a reputation for being “the weedy one”. Gardeners who are delighted by its delicate-looking and well-mannered cousin may shudder at the thought of growing this vigorous, summer-growing plant.
You can identify it by the different roots (its hanging threads have fine side-threads) - but you usually know if this is the one you have, just because it grows so fast. If you have a smothering blanked of fern, this is your species. It's the one that forms a brick-red sheet in the summer sunshine.
On a sheet of natural water, this fern is not a problem. It provides habitat for a multitude of little creatures, which become food for fish and birds. It reduces water temperature and evaporation, so our wetlands last longer into the dry season. It does no harm to stock which drink the water.
It can be a weed, though. 
It is often seen reproducing at a crazy speed in summer, doubling its biomass every two days and making a brick-red sheet which can cover dams, impede water flow and navigation, clog pumps, and starve other plants of light and oxygen.
The cause of out-of-hand growth is usually a high nitrogen level in the water - a common modern problem of agricultural techniques which don't necessarily get the mix of chemical fertilisers just right, or animal husbandry techniques where animal wastes make their way into the environment.

Added to this, Ferny azollas don’t just guzzle the nitrogen that’s available to them in the water. They  have the ability to fix more of it, from the atmosphere - part of the secret of their rapid growth-rate. They do need help from a friend to achieve it. A nitrogen-fixing bacterium of the blue-green alga type (Anabaena azollae) lives in little cavities on the backs of their leaves.
The side effect is that those little plants convert themselves into what can be used as a rich, high-nitrogen fertiliser - and they do it for free.

Rice farmers in Vietnam add chemical fertiliser to their flooded paddy fields, when the little rice plants are newly planted out. This produces such a thick bloom of Azolla pinnata that it smothers weeds, and is said to prevent mosquitos from breeding. When the fields are dried out, the fern dies, making a rich mulch which releases its nitrogen to the crop as it decays.
We could adapt the technique, scooping plants off dams and ponds to add to the compost heap or use as mulch. Killing the plants is not a problem. As soon as they dry out, they’re dead.
Meanwhile, Azolla’s ability to draw such a lot of nitrogen out of the water, doubling its leaf area every week, has another useful function. It has proven to be a valuable tool in control of the blue-green algae which have become such a problem in our inland waters.
 Azollas can clean up infected dams and waterways, starving the algae by their aggressive removal of nitrogen. The task needs to be completed, of course, by removing the ferns from the water. Leaving them to die in situ only lets the nitrogen be released back into the water. Harvesting is a relatively easy chore because of these little ferns' surface-floating habit. There's no need to remove it completely. The bits left will keep doing their job until a slow-down indicates that there's just not so much excess nitrogen in the water any more.
This practice can also help clear up nasty-looking (and perhaps nasty-smelling) water in garden ponds.
Azolla is also used as a nutritious fodder for cattle, pigs, ducks and chickens.

Both Azolla species are very tolerant of pH variations, thriving in water from 5.5 to 7.5.