IT HAS been called the botanical find of the century: a lonely stand of
conifers, the last of their kind and thought to have been extinct for
aeons鈥攗ntil three bushwalkers came across them one sunny winter
afternoon.
The 23 odd-looking pines, stretching up to 40 metres through the canopy of a
deep and inaccessible gorge in Australia鈥檚 Wollemi National Park, are from a
group that once covered the southern supercontinent of Gondwana. The trees were
thought to have disappeared long before humans walked the Earth鈥攗ntil
David Noble and his companions stumbled upon them. 鈥淭hey just looked a bit out
of the ordinary,鈥� says Nobel. 鈥淪o I popped a cutting in my pack and took it back
home to try and identify it.鈥�
Back at his Blue Mountains home west of Sydney, the keen canyoner and student
of botany was unable to match the sample with anything in the textbooks, so he
later showed it to Wyn Jones, a colleague at the National Parks and Wildlife
Service. Jones has spent most of his life studying rare plants of the Blue
Mountains. 鈥淚 thought that it was just a fern,鈥� he says recalling that morning
in August 1994. 鈥淯ntil Nobel said, `It鈥檚 a bloody great tree!鈥�. And that sort of
shocked me.鈥�
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A month later the two retraced Nobel鈥檚 original route back to the site to
collect more specimens. This was no easy task: the Wollemi National Park is a
sandstone massif covered in eucalyptus woodland and scrub, peppered with
isolated patches of rainforest. Its 496 000 hectares are criss-crossed with
hundreds of densely vegetated canyons ranging from a few metres to many hundreds
deep. To reach the site, the search party had to abseil 400 metres down the side
of a precipitous gorge in stages, and then pick their way through thick foliage
alongside a creek.
Once there, Jones realised that he had surveyed this area from the air some
five years before, coming within a few hundred metres of the pines but not
noticing them. Up close, however, they were distinctly unusual. Strange nodules
covered the trunks, making the bark look like bubbling chocolate. The tallest
tree had a single trunk measuring about a metre in diameter, but many had
between 10 and 20 smaller trunks sprouting from their base. The trees had a
unique branching pattern, with successive whorls of primary branches emerging
from the trunks. And to top all this, there were the odd, fern-like leaves which
Jones had commented on鈥攕tiff and yellowish green on the mature trees but
dark green and with a waxy underside on the juvenile trees.
What has astonished botanists above all, however, is that these prehistoric
giants were living within 150 kilometres of Sydney, Australia鈥檚 largest city, in
a country with a well-developed scientific infrastructure and a long history of
botanical research. Many researchers have marvelled at the fact that a new genus
of pine could be uncovered on the doorstep of a city of four million people.
鈥淭his reminds us that we don鈥檛 know as much about the world as we keep thinking
we do,鈥� says Don Blaxell, senior assistant director of the Royal Botanic Gardens
in Sydney, which has been responsible for most of the research into the new
genus.
What that research reveals is that the trees, named Wollemia nobilis
鈥攑artly in homage to Noble and partly because of their majesty鈥攁re
both surprisingly unusual and remarkably ordinary. The Wollemi pine is a
conifer, a group of seed-bearing trees dating back to the Carboniferous era more
than 300 million years ago. It is a member of the ancient conifer family of
Araucariaceae, until now thought to include only two surviving genera:
Araucaria and Agathis. In many ways, the new genus appears to be
somewhere between these two.
The Araucariaceae family first appears in the fossil record in the Triassic,
250 million years ago鈥攁round the time that the sandstone massif of the
Wollemi National Park emerged. It seems to have been most widespread between 200
and 65 million years ago, from the Jurassic to the Cretaceous periods, when it
grew all over the planet. Then, at the end of the Cretaceous, just when the last
big wave of extinctions claimed the dinosaurs, it began a dramatic retreat and
disappeared from the northern hemisphere altogether.
Missing records
Nonetheless, the family remained an important part of the forests of the vast
southern supercontinent of Gondwana until the middle of the Tertiary, some 30
million years ago. Then began a slow decline in range and diversity, as
flowering plants came into their own.
The fossil record contains no Wollemi pines. The closest match yet found is
between Wollemi pollen and fossilised pollen that was previously something of a
mystery. Known as Dilwynites, it had been considered part of the ancient conifer
family of Araucariaceae, but no one could agree on which genus. The pollen is
abundant in the fossil record of Australia, New Zealand and Antarctica from
about 94 million years ago until the middle of the Tertiary period. Its range
and diversity plummets after Australia鈥檚 split from Gondwana and its drift north
30 million years ago. It was probably affected by the dramatic change in the
Australian climate that followed, from uniformly wet to drier and highly
erratic, as it is today. The last known occurrence of the pollen in the
subsequent sporadic record comes from oil drilling in the waters between
northern Tasmania and the Australian mainland, dated at two million years.
From then on, the fossil record is silent. Everyone had assumed that the
genus to which Wollemi pines belong had been extinct for millions of
years鈥攋ust one more curiosity for botanists to argue over. So how did this
single stand of trees survive? And why? Here the mystery deepens.
Secret gorge
Since the pine鈥檚 discovery, botanists have scoured the park for more of the
ancient trees. In three years they have uncovered just one more stand of 17
trees, at an even more secluded spot about a kilometre upstream from the
first鈥攖he exact whereabouts of the gorge is kept secret to protect the
trees. If they were once abundant throughout the continent, why have they
survived the millennia in this one rainforest nook among the many rainforests in
the southeast and northeast of Australia? And why in this one isolated
gorge?
鈥淚t鈥檚 just there, and we have no real understanding of why,鈥� says plant
pathologist Brett Summerell of the Royal Botanic Gardens. 鈥淚t鈥檚 in a very deep
gorge, but there are others next door that are just as deep and just as
inaccessible; there are similar soils, similar light regimes and similar creeks
running in the same direction. Apart from the Wollemi pines being there, it鈥檚
like any other gully in the Wollemi National Park or the [nearby] Blue Mountains
National Park. It鈥檚 very puzzling.鈥� Summerell suggests that unlike its closest
relatives in the same genus, the Wollemi pine may never have been very
widespread. If it was highly specialised to fit a particular ecological niche,
it could have been confined to the wet eastern rainforests of Australia. Such a
limited distribution would have made eventual isolation more likely.
Whatever the history of the genus, there is no doubt that the remaining trees
have been isolated for a very long time. To find out exactly how long,
ecological geneticist Rod Peakall and his colleagues at Canberra鈥檚 Australian
National University have spent the past year studying the genetic diversity of
the genus. Because inbreeding reduces genetic diversity over time, establishing
how much variation there is between members of a particular group allows
scientists to estimate how long a species has been reproducing within that
narrow population.
So Peakall鈥檚 team analysed genetic markers in eight adult trees from the
first stand and four from the second. Using a standard assay, allozyme
electrophoresis, the team searched the DNA for differences in allozymes, the
genes that code for enzymes. They compared between 30 and 40 sites on the
genomes of each of the 12 samples. The result: zero variation. This was
surprising, but not astounding: small, isolated populations tend to have limited
genetic diversity, and their assay has on rare occasions failed to find any
variation. For a more detailed look, the team used a recent version of DNA
fingerprinting called AFLP (amplified fragment length polymorphism), which
compares thousands of points on a genome. This technique, which is 50 times more
powerful than the allozyme method, has always turned up trumps.
Complete clone
But not this time. Peakall was left stumped. With no differences in the
genes, and without baseline data on normal levels of variability, it was
impossible to establish how long the trees had been isolated. 鈥淗ow can you put a
comparison on zero?鈥� says Peakall.
While the search for genetic variability is not over yet, the results
strongly suggest that the pines have been a small population isolated for
millennia. The other possibility is that trees are in reality clones of a single
remnant organism that has been propagating purely through coppicing for a very
long time. Here, the tree extends its roots horizontally and grows another stem,
which then develops into a fully fledged tree that loses the original root
linkages over time. At one of the sites, a group of 160 stems appear to be part
of a single individual. Such trees may be extremely old. 鈥淭here鈥檚 no doubt that
with the Wollemi pine, there鈥檚 local cloning caused by this root coppicing,鈥�
says Peakall. 鈥淭he question is whether it goes beyond that: is there an
underground root system, and were they once all the same organism?鈥� But proving
this latter theory might require uprooting some of the trees, which are
considered too precious.
If they are indeed clones, the fact there are two sites some distance apart
makes it hard to imagine that all the trees came from one individual. The lack
of genetic diversity may be a combination of both isolation and clonality. And
the cloning process itself gives a clue about how old the stands may be:
non-sexual propagation on this level would take many generations to develop.
Assuming similar growth rates to that in related genera, the oldest trees are at
least 1000 years old. Peakall鈥檚 best guess is that they have probably been
isolated for between 6000 and 10 000 years. 鈥淲hether this stand has been
isolated for two million years or less we just cannot tell,鈥� says Blaxell. 鈥淚鈥檇
say it鈥檚 probably tens of thousands, if not hundreds of thousands of years.鈥�
Seeds of success
What has confused researchers is the ease with which they have been able to
cultivate new pines from seed. They had feared that the decline of Wollemi
pines, and their apparent enthusiasm for asexual reproduction, might be the
result of poor seed viability. But over the past two years, more than 1300
seedlings have grown successfully at various greenhouse sites. Many of the
saplings are more than a metre tall and show no difficulty coping with
conditions outside the Wollemi National Park.
If sexual reproduction functions adequately, why does the Wollemi pine
endlessly clone itself? 鈥淭his natural clonal capacity is interesting,鈥� says
Peakall. 鈥淵ou can actually force some of the other conifers to do the same thing
by chopping them down or causing other major disturbance. But they won鈥檛 do it
naturally, which this seems to do. It鈥檚 meant that it has been able to hang in
there for a very long time and not be reliant on sexual reproduction.鈥�
The clonal nature of the trees, if proven, makes it even more imperative that
they are protected because any introduced disease that killed one would probably
kill them all. The State of New South Wales has special laws protecting the
pines, as well as a big recovery plan. 鈥淭here are a number of programmes under
way looking at what conditions they grow best under, what sort of pH in
the soil, what sort of fertilisers and light conditions,鈥� says Summerell. 鈥淚t
grows quite well from both side-shoot cuttings and top-growth cuttings, and
grows quite well from seeds, which can be stored using relatively conventional
迟别肠丑苍颈辩耻别蝉.鈥�
When the recovery programme began, little was known about the Wollemi.
Botanists feared that climbing the trunk with spiked boots to collect cones from
near the tree鈥檚 apex might be damaging. So seeds were collected from treetops by
volunteers swinging from helicopters. This proved dangerous and not very
effective: when the helicopters came close, the downwash blew away many cones,
and when they moved higher, the volunteers on wires would sway precariously.
Finally, the botanists put nets beneath the trees to collect the seeds.
It has all been such a success that the Botanic Gardens are turning over the
mass production of the pines to private horticultural companies so seedlings can
be sold internationally. The Gardens will control the rights to the progeny,
putting money earned by selling seedlings back into research. By late 1998,
production could reach hundreds of thousands per year.
鈥淧art of the conservation and preservation strategy is to get it out as
widely as possible, so anyone can buy one,鈥� says Blaxell. This is not just a
money-making venture; it鈥檚 also the best guarantee that the original site will
remain protected. 鈥淭he Wollemi has generated so much interest that unscrupulous
collectors might go to the site and damage the trees or introduce some disease.
We don鈥檛 want to lose it,鈥� Blaxell says.
For now, anyone curious to see this biological time capsule from the Jurassic
can go to the Royal Botanic Gardens in Sydney, where two juvenile pines are
growing behind glass. In September, London鈥檚 Kew Gardens received a pair of
saplings that will eventually go on display, and gardens around the world will
be sent specimens in the next year. The Wollemis, only a few years ago staring
at the abyss of extinction, now have a second chance.
