Lush Life

An Australian sand plain with wretched soil mysteriously yields more diversity than a rain forest

By Tim Flannery, Martin Mischkulig|Wednesday, December 03, 2003

In Australia’s sandy southwestern corner, a barely perceptible topography stretches as far as the eye can see. Even spiny, knee-high bushes can’t cloak the skeletal soil, and in summer the heat is so intense that haze swallows the horizon, and wind is the only sound to be heard.

The kwongan is a biological marvel in southwestern Australia that bursts into bloom each spring. This habitat has been designated one of the world’s 25 most biodiverse regions and is home to more than 3,600 plant species. About 2,700 species here cannot be found anywhere else on Earth. The photographs on the following pages were taken in two areas within 100 miles of Perth.

But a closer look reveals one of the most diverse plant communities on Earth. In spring the land bursts into uncountable blooms of breathtaking color and shape. The Nyungar natives of Australia named this region the kwongan, and today its blossoms attract tourists from around the world.

My first view of this bizarre ecosystem came in 1973 from the seat of an Italian Moto Guzzi motorcycle I had ridden from my home in Australia’s southeast, more than 2,000 miles away. For several days I traveled relentlessly across the featureless Nullarbor Plain on a national highway that had not yet been paved. As I entered the better-watered southwest, the scenery refused to improve. The monotonous kwongan baked under a harsh sun. Many of the plants were perched on stilt roots that held their main stems a few centimeters above the surface, as if the soil had eroded under them. It hadn’t, but like most things here, no one has a satisfactory explanation for it.

Most of the bushes looked almost dead, but I could see taller growth ahead. When my eye caught a flash of brilliant orange, I eased the throttle and came up on blooms of orange banksia (Banksia prionotes), six-inch-long cones packed with hundreds of tiny spiraled flowers that turn the snowy white structure flame orange as they open from the bottom up. The cones were dripping with nectar and had attracted beetles, flies, and other insects. Beneath the flowers grew strange, stiff leaves that looked as if they had been cut with pinking shears. The flamboyance seemed out of place on this parched, dusty roadside. Why did this struggling plant expend so much precious energy on flowers, and why was it wasting so much moisture producing nectar in the midst of summer?

A

(A) Australia is home to many carnivorous plants, including members of the genus Drosera (called sundew). The plant’s sticky glands trap insects, which are slowly digested and absorbed. (B) The blossoms of Gastrolobium, a pea called prickly poison, contain toxic compounds.
In the years following my motorcycle journey I became a biologist and found myself pondering that strange vegetation once again. But the more I learned, the more baffled I became. Many of these plants are carnivores, for example, that eat insects. Some others, like a type of mistletoe that grows here, are imposing trees that suck the life from nearby, lesser plants. Still, it was the flowers that captivated me and posed the most difficult questions. Some looked as if they had been crafted in enamel, while others had great fuzzy heads, like torches. Some, I learned, bloom deep underground. This is a world of diversity, abundance, and downright outrageousness.

The mystery deepened as I learned about the strange pollinators that serve some of the flowers. One is a mouse-size marsupial that eats nothing but nectar, pollen, and small insects—the ecological equivalent of a flightless hummingbird. Why has such a marvel evolved? At first I believed the curiosities were unrelated, but research has shown that many stem from a single strange attribute of the region’s soils.

C

D

(C) A landscape of wildflowers—including a species known as paper daisies—stretches into the distance at Coalseam Conservation Park in southwestern Australia. (D) The nectar-tipped blossoms of Banksia prionotes unfurl from the bottom up to look like a bottlebrush. The plant is one of 76 species of Banksia in Australia. The genus is named after Joseph Banks, the botanist who traveled with Captain Cook on his voyage to Tahiti, Australia, and New Zealand. The taxonomist Linnaeus later suggested that Australia be named Banksia in honor of Banks's contribution to Australian natural history.

The kwongan is one of only a few habitats on earth with a Mediterranean climate—hot, dry summers and cold, wet winters. Others are found in South Africa, California, and of course, southern Europe. These regions depart from the dominant pattern of plant biodiversity: They support so many plant species they can rival rain forests, which are widely accepted as the richest areas of flora on our planet. The rain forests of Panama, for instance, have about 8,000 species of plants, and the rain forests of Africa’s Ivory Coast support about 4,000. That diversity can be matched in Mediterranean climates. South Africa’s fynbos sand plain, for example, has about 8,000 species, and the kwongan has 3,600. There is another surprise in this desert: The kwongan outdoes any rain forest anywhere in its diversity of species per square foot. In just 500 square feet of kwongan a biologist can find as many as 100 species of woody plants.

Paradoxically, the kwongan’s diversity is provided by only a few plant families. Just three—

E

F

(E) A Banksia prionotes bush in bloom. (F) The fruit of the woody pear (Xylomelum angustifolium) is encased in a hard, velvety shell about the size of an ordinary pear. Each pear contains two edible seeds.
the myrtle, pea, and protea families—account for half the species in any one area. Researchers have argued for years about the causes of this peculiarity, but recently a remarkably counterintuitive argument has gained ground: Poor soils can foster the growth of rich plant communities. In Australia’s case, the southwestern province encompasses some of the most ancient continental crust on Earth. The landscape has remained unchanged for hundreds of millions of years, without mountain building or volcanism or glaciers. The region has experienced only a slow leaching that stripped the soil of almost everything except quartz.

The soil is so infertile that agriculture here is best described as hydroponics—farmers add nutrients to a sterile medium, and when

G

H

(G) Two Xanthorrhoea drummondii shrumbs called grass trees rise above the sand plain. Aborigines named them balga, meaning "black boy," because fires often burn away the bottom leaves, leaving a humanlike silhouette. Usually balgas grow little more than an inch a year; after a fire, they can grow almost five inches in a season. The shrubs are old; they were dominant Australian vegetation when dinosaurs roamed the continents. (H) A lizard basks in the sun with Verticordia chrysanthella, a type of wildflower, in the background.

the rains come, the crops grow. The strategy works only in the short term, for under the sandy kwongan soil lies salt. When deep-rooted native vegetation is destroyed during attempts to farm, a salty water table forms that slowly rises, killing all.

Far too little phosphorus is another significant problem. No nutrient may be more essential to life than phosphorus, but the levels here are so low that few plant families can cope. Nonetheless, those that do survive tend to be spectacularly successful. In the 1970s David Tilman of the University of Minnesota published a fundamental insight into this mystery. He argued that in specific ecological niches, such as wetlands or hardwood forests, plant species that grow most rapidly come to dominate because they monopolize resources. Cattails and sugar maples are examples of those species, which Tilman called superspecies. In areas where soil nutrients are limited, such species cannot take hold. Instead, a series of specialist species may learn to coexist.

On the monotonous sand plain, for example, the terrain varies just enough to offer options for specialists. One species can flourish around tiny hollows where a bit more phosphorus accumulates; another can tolerate the dryness of a slightly higher elevation; and yet another may thrive on the midslope.

I

J

(I) A species of Drosera proffers its sticky glands to prospective insect victims. (J) A bush flower, Conostylis canteriata, blooms in bunches.
The poor soil promotes other survival strategies. Take, for example, the delicate, glistening carnivorous sundews (Drosera). Sixty-eight of the more than 160 sundew species in the world thrive in Australia’s southwest. During the wet winter and spring, their sticky leaves are astonishingly effective at trapping insects. One species found near Perth (Drosera erythrorhiza) eats an average of 80 tiny arthropods a day in spring. Another similar carnivore (Byblis gigantea), which belongs to an entirely different plant family found only in Australia, can trap four flies per centimeter of each leaf’s length. Insects provide the plants with an essential supply of nitrogen, phosphorus, potassium, sodium, and zinc.

Still, most kwongan plants cannot trap insects. So they obtain a portion of their nutrients from mycorrhizal soil fungi, which live on the roots of plants and help import nutrients. The fungus

K

L

(K) The carnivorous Drosera erythrorhiza lies close to the ground in order to trap insects as they walk over it. (L) Black kangaroo paw (Macropidia fulginosa) looks black because a dense layer of black fibers covers the green stalk and the flowers. The kangaroo paw, named for its distinctive shape, is Western Australia's floral emblem.
generally derives some benefit from the relationship by drawing on carbohydrates manufactured by its plant partner during photosynthesis. But a few plant species have managed to so thoroughly exploit the fungus that they no longer make any of their own food. For example, the underground orchid (Rhizanthella gardneri) has given up photosynthesis; it flowers and fruits deep in the earth, where it must be pollinated and dispersed by burrowing invertebrates.

The orchid is not alone in its thievery. At least 42 other kwongan plant species get by as outright parasites. One is the Christmas tree (Nuytsia floribunda), which earns its name from the great masses of flame orange flowers that appear around it each summer. The blooms of this type of mistletoe look like great clusters of brilliant orange grapes and can seem hallucinatory in the summer heat. It lives by sucking the life out of grasses and lesser plants growing within its reach. The roots are armed with structures called haustoria, which throw a collar around the rootlets of neighbors. Spigotlike outgrowths from the collar pierce the roots

M

(M) Dryandra nobilis, or golden dryandra, has thistlelike blossoms and barbed leaves. The plant is named after Jonas Dryander, an English botanist who described many Australian plants that Captain Cook brought back to England after his first voyage around the world. Although Dryander was originally slated to be aboard with Cook, he decided to remain in England with his family, and botanist Joseph Banks joined the crew instead. Perhaps Dryander made the prudent decisions: Only two of the eight men Banks took along survived the voyage. (N) Lachnostachys eriobotrya is called lambswool or lamb's tail.
and drain off nutrients and moisture. Its discarded leaves, which contain considerable nitrogen and phosphorus, create a niche for herbs growing under the tree’s canopy.

Other plants rely on less predatory methods. The banksia and other members of the protea family extend roots across the soil surface to collect the tiny amount of nutrients that come with rainfall or decaying plant matter. To fund extravagant summer blossoms, an extraordinary taproot penetrates deep into the earth to reach sweet groundwater and less-weathered rock.

In spring, after a wet winter, the kwongan goes berserk. Some bushes obscure foliage with red, white, and blue flowers, while others produce compound flowers that look like pinecones, toothbrushes, even feather boas. At first, the astonishing floral exuberance seems puzzling, given the limited conditions. But plants actually expend little of their nutrient store to make flowers. All that is needed to produce nectar is sunlight and water, and during the Australian spring both are abundant in the southwest. The real challenge is spreading pollen. Without nutrients, potential pollinators such as insects and birds are scarce, and the appetites of carnivorous plants compound the problem. Each plant must therefore compete intensely to attract a pollinator. Only the most handsome and nectar-filled blooms win out.

Against a backdrop of scarcity and struggle, the features of the honey possum—an important pollinator—no longer seem strange. Tarsipes rostratus is the sole surviving representative of an ancient marsupial family found only in the southwest of Western

O

(O) This close-up of lambswool shows the flower's fuzzy blooms.  (P) Drosera micrantha offers pink blossoms to pollinators while trapping other potential pollinators, such as the insect seen on the right, on its sticky glands.
Australia. It is also the only land mammal on Earth that subsists mostly on flower nectar and pollen, which it probes for with an elongated muzzle. Many aspects of its biology are even more surprising. The male’s huge testes make up 4 percent of its body weight (human testes of this proportion would weigh about two kilograms, or 4.4 pounds each), and the tiny animal’s sperm are larger than those of the blue whale. With the abundance of protea and myrtle species and their diverse flowering schedules, the honey possum thrives year-round, sometimes extracting all the food it needs from just 430 square feet.

Some kwongan plants have evolved chemical defenses and manufacture poisons to keep their leaves from being eaten. Gastrolobium peas produce fluoroacetate, a poison so deadly that just one mouthful of leaves can kill a sheep. Acidic compounds such as tannin and phenolics also are favored, and their presence in shed dead leaves prevents their consumption by soil invertebrates.

 

Q

R

(Q) A single white blossom tops Drosera marchantii. (R) The many sticky, insect-trapping glands of Drosera stolonifera glisten like a fringe of dewdrops.

The accumulation of leaf litter in a dry climate sets the stage for periodic fires. Every few decades the kwongan is reduced to ashes. Although a few species resprout from woody, underground rootstocks, most plants are killed. Then woody, hard seed capsules created by many of the plants open, sometimes after years of dormancy, to release seeds into a rich bed of ash. With the winter rains, the seedlings emerge, and the cycle begins again.

The kwongan is slowly yielding its secrets, but the ecosystem remains poorly understood. As taxonomic studies are undertaken, puzzling new species are coming to light. The secrets here are as old as time itself—and may take just as long to uncover.

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