Mulga; face of the inland

This is another in an irregular series on (mostly Australian) trees. It's been a while since I posted one of these, but you can find some past ones here, here, and here. 

It is a remarkable fact that some 20-25% of the entire continent comprises semi-arid woodland dominated by just one tree - the hardy Mulga, Acacia aneura. 

Map of Mulga range from Atlas of Living Australia; in fact this map implies a greater even than
25% coverage, but I think the significant word is 'dominated'. This map includes more scattered stands,
in addition to the vast areas with just one dominant species.
(And I think we can discount records from Brisbane, Victoria and Adelaide, as well as up towards
the Top End, as being either errors or plantings.)

A drive through the inland of Australia can involve hundreds of kilometres of this habitat; these three photos show Mulga plains in different parts of Australia.

From Chambers Pillar, south-east of Alice Springs, central Australia.

Near Quilpie, south-west Queensland.

Idalia National Park, central Queensland.

Having made the claim about 'one species' however, it may not be quite that neat, as nature is wont to do to our attempts to create tidy little boxes. It is certainly a very variable species (which is perhaps not surprising over such a vast range), with very different foliages.

Mulga near Windorah, south-west Queensland; note the slender foliage.

Mulga near Cobar, central western New South Wales.
Here the foliage is much broader, giving a quite different aspect.

One thing that is consistent however is the distinctive form, which has been described as like an upside-down umbrella. 

Mulga near Windorah, south-west Queensland.

The erect phyllodes (modified leaf stems in acacias, which function as leaves) direct rain down the stem and ultimately down the trunk, so that virtually all the water which hits the canopy enters the soil less than 50cm from the trunk in old trees, and even closer in small ones. 25mm of rain can, in this fashion, be equivalent to a fall of 140mm where the water enters the soil; it follows the trunk down through the soil to the roots, which take the water deeper and thus hold it longer than can be done by other more shallow-rooted plants. In addition of course any plant which grows under the Mulga canopy is going to be robbed of rain by the tree.

Another constant, as we'd expect from a species, or even a species complex, is the flower, which forms a spike of clustered little flowers, as opposed to the sphere of many acacias.

Mulga flowers, near Windorah, south-west Queensland.
Mulga produces heavy crops of flowers following spring and summer rain,
but only produces seed after late summer rains.
Moreover for actual seed set to occur, follow-up winter rains are needed too. The seeds drop after October-November,
then need more summer rain to germinate. This set of circumstances may only come along once a decade or so.

Mulga grows in a range of habitats (so the long drive through the Mulga lands can never be boring) but one constant factor seems the iron-rich red soils, as you've probably already noticed in the photos above; here are some more examples.

In sandy clay plain, Idalia NP, central Queensland.

Growing on a harsh stony plateau, above Trephina Gorge, East MacDonnell Ranges, central Australia.
Below them, in the relatively sheltered creek bed, is a River Red Gum E. camaldulensis.

On a stony escarpment above Palm Valley, central Australia, with spinifex hummock grassland Triodia sp.

On a lunette sand dune above a dry salt lake, Great Sandy Desert.

I'm sure that you've noticed too that Mulga is tough, with regard to its ability to survive very harsh dry conditions. Drought is part of its every-day existence, but somewhat counter-intuitively it doesn't grow where either summer or winter are always dry - perhaps here other species are better adapted, though I've not worked through this one properly yet. 

Mulga in severe drought, near Lightning Ridge, northern New South Wales.
The Mulga is surviving, where not much else is.

 One thing that Mulga does not cope with well however is regular fire; it can regrow to some extent from underground buds, but not from trunk buds, as eucalypts do so well. It regenerates well from seed, but if the next generation of seedlings is killed by another fire before setting seed the population is in trouble.

The next two scenes of burnt Mulga are from central Australia.

Plenty Highway; some regeneration from underground buds.

Watarrka (Kings Canyon) National Park; a very intense fire and no regeneration here yet.

The term 'mulga' is also used widely as a name for the habitat; 'mulga lands' is a common descriptor. We've stressed the prevalence of dry conditions in these lands, especially when El Niño grips the lands, but there are good times too, when the rains do come and the mulga lands burst with life.

Massed flowering in (and of) the Mulga, Paynes Find, inland Western Australia.

A reflection of this use of the term is in the other organisms with mulga in the name; here are a couple.

Mulga Parrot Psephotus varius; a beautiful bird, which in fact can be found in pretty much
every arid habitat across southern Australia.

Mulga Ant nest, Polyrachis sp.
These big nests, protected from cross-ground flooding and erosion by carefully placed mulga litter,
are common in the mulga lands. Other Polyrachis species built turret nests for the same reason.

And just in passing, other acacia species are also referred to as 'mulga', with an adjective, including Red Mulga A. cyperophylla.

Red Mulga, Mount Magnet, inland Western Australia; also known as Miniritchie, along with
other species with similar bark.

I hope this has brought back some good Mulga memories for you, but if they are still in your future, perhaps this can encourage you to bring your trip forward in time.

To assist with it, here are the start and end of a day in the mulga lands, this time in the Great Sandy Desert, in eastern Western Australia.

Sunrise on Mulga...

... and sunset through it.

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Boodjamulla (Lawn Hill) National Park; a remote and superb oasis

Boodjamulla is remote, over 200km from the nearest small town, Burketown, with the latter half of that journey on sometimes trying corrugated dirt roads. It is tucked away in the arid far north-west corner of Queensland, not far from the border of the equally sparsely populated Northern Territory. And it is worth the undoubted effort of getting there, tens of times over. Veritably an oasis preserving a remnant of a distant moister time, in a stark and beautiful semi-arid woodland landscape that is known as the Gulf Savannah, it is one of the most beautiful parks in the continent.

A section of the gorges, with fringing monsoon forest and arid spinifex hummock
grassland and woodland on the raised escarpment.

Approximate location of Boodjamulla NP, in the hinterland of the Gulf of Carpentaria.

The camping area is basic, without power but with a modern toilet and shower block, and is just metres from Lawn Hill creek whose deep aqua-green waters provide safe swimming - a rare commodity indeed in the Australian tropics. From here some 20 kilometres of walking tracks fan out across the surrounding countryside, up onto ridges with grand views, and along the creek and its gorges. I'll start however with the context, the rocky hills and woodland plains in which the cool green gorges are such a delightful surprise.

The walk up and across the nearby Constance Range, south-east from the campground, is an excellent introduction.

Constance Range walk, one best done early in the day.
The trees are Ghost Gums, probably Corymbia (Eucalyptus) aparrerinja, though there
are also some very similar species with more limited distributions here.

The bloodwood Corymbia (Eucalyptus) dichromophloia is another which thrives in this apparently
harsh landscape of broken stones.

The plains below, hinted at in the previous photo, stretch far into the distance from various lookouts along
the loop walk. The access road cuts across the foreground.

From the other side of the range, the view is back to the narrow green strip of monsoon forest that follows the creek; it is in striking contrast to the dry hills on which we are standing, and to the plain between us and the creek.

Looking over the spinifex to the creek line in front of the cliffs; the brighter green of a patch
of the palm Livistona rigida, a species scattered in north-west Queensland and the Top End, as well as,
unexpectedly, in the ranges of central Australia where it has been suggested that humans may have
been responsible for their appearance.
At Lawn Hill they are part of the relict environment from more humid times that survives in the sheltered gorges.

On the hills the plants are very different.

Turkey Bush Calytrix exstipulata (Family Myrtaceae) is a widespread shrub across drier tropical Australia,
and always a delight (above and below).

 

The equally attractive Grevillea dryandrii is likewise widely scattered across the north.

Mulla Mulla Ptilotus sp. (Family Amaranthaceae) and spinifex Triodia sp.,
two important components of the herb understorey.

Animals are less obvious out on the dry rocky tops, but of course they are here, even in the daytime.

Grasshopper, as usual unidentified (by me...).

Ring-tailed Dragon Ctenophorus caudicinctus, a lizard with a huge range across the arid
north-west third of Australia.

Another series of walks heads west from the campground, and provides a series of access tracks north across the low escarpment to the gorges. Before doing so the route gives a taste of the plains and the cliffs, the other side of which is the gorge.

Stand of Ghost Gums with termite mounds.

The gorge is just beyond these cliffs, above and below.

A short climb and the contrasting view is breathtaking.

Indarri Falls, from above (with palms),
and from down at waterlevel.

 

Fish are abundant in the limpid waters.

Sevenspot Archerfish Toxotes chatareus.

It would not be possible to exaggerate the pleasure of this arrival on a hot morning! When we finally leave refreshed we re-ascend the escarpment to more stunning views, including the one at the beginning of this post and this one, looking back to Indarri Falls.

Another excellent way of seeing the waterway is by canoe, which can be hired at the camp ground. It's a different perspective again.

Dense riverside vegetation.

Figs on rockface; the one on the right has managed to reach the water via its roots, with obvious benefits!
The one on the left is still striving for nirvana...

Freshwater Crocodile Crocodylus johnsoni; it is wonderful to be able to approach these somewhat timid fish-eaters
so closely. It is unfortunate that when the excellent 19th century zoologist Gerard Krefft named this animal for
naturalist-policeman Robert Johnstone (who brought it to Krefft's attention) he misspelt the name. Oops...

Back at camp we can walk downstream where the water isn't backed up, through the riverine forest; we were there at the end of the dry season.

Walking track through tufa, a form of calcium carbonate (like limestone, but much less dense)
deposited from mineral-rich water

Flood debris, an impressive reminder of what goes on during the wet season in our absence!

Big Leichhardt Tree Nauclea orientalis (Family Rubiaceae).
The species is usually found along watercourses, from northern Australia to south-east Asia.

These graceful big paperbarks, Melaleuca fluviatilis, are found only in northern Queensland.

Nearer to camp the much wider stream is flanked by palm-dominated monsoon forest.

Open streamside forest (the water is visible behind) of Livistona rigida and Melaleuca fluviatilis

Some rather special birds live in this forest, including these two.

Buff-sided Robin Poecilodryas cerviniventris. John Gould in the 19th century recognised this as a separate species from the east coast
White-browed Robin P. superciliosa, but 20th century ornithologists disagreed; it was only 20-odd years ago that opinion swung back to Gould's position. This elegant little robin loves the streamside monsoon forests.

Purple-crowned Fairy-wren pair Malurus coronatus; he (on the left) is just coming into
breeding plumage. Later he will have a glorious rich lilac crown, with a little black patch in the centre.
This lovely bird is restricted to paperbark and stream-fringing vegetation in two populations,
straddling the western and eastern borders of the Northern Territory.
It is threatened by clearing and burning of its habitat.

The campground itself is amazingly rich in birdlife, assisted by the dripping taps, fed from the creek; here are some in and around our site.

Crimson Finch Neochmia phaeton, a beauty from northern Australia and New Guinea.

Bar-shouldered Dove Geopelia humeralis, a common dove of northern and eastern Australia with
Double-barred Finch Taeniopygia bichenovii and Crimson Finch.

White-gaped Honeyeater Stomiopera (until recently Lichenostomus) unicolor.

Female Red-winged Parrot Aprosmictus erythropterus, a truly beautiful bird;
the male is considerably more striking still.

The same bird a moment later; try to think of it as arty rather than blurry...

Great Bowerbird Chlamydera nuchalis.

Great Bowerbird at his bower, only metres from the campground.

It is a spectacularly special place. One warning though. Some years ago the hitherto sensible Queensland Parks Service (presumably under some political pressure to reduce on-ground staffing) introduced what I see as a very inappropriate booking system, requiring us to book online before arriving, with no flexibility and no possibility of spontaneity. There is no option to extend a stay if you're enjoying yourself unless you can get online (not likely in most parks!) and can't just drop in. Moreover you have to nominate a site number without seeing the setup! (Mind you, at Boodjamulla you'll find when you get there that your carefully selected site is irrelevant...) So, make sure you're very organised before you go, and err on the side of caution if you think you might want to stay on for a day or so.

It's worth it though; there are not many lovelier places to pass some time.

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