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I've been a Canberran since moving here from Adelaide on the first day of 1980. I now live in suburban Duffy with my partner Louise Maher, ABC 666 radio and on-line journalist. Among my early memories is following Sleepy Lizards (Shinglebacks) around the paddocks north of Adelaide, guarded by the faithful bull terrier. I have always been passionate about the natural world, trying to understand how it works, how the nature of Australia came to be, and sharing those understandings. My especial passions are birds, orchids and mammals. For much of my life I have been a full-time naturalist, running bush tours, writing books etc, doing consultancies, presenting a regular radio slot on local ABC, chairing a government environment advisory committee and running adult education classes. Recently I have eased back somewhat, but am still writing, teaching, doing some radio work and running overseas tours - as part of my fascination with our Gondwanan origins I've been running tours to South America for the past decade. I was awarded the Australian Plants Society Award in 2001 and the Australian Natural History Medallion in 2006, both for services to education and conservation.

Tuesday, 17 June 2014

Featuring the Fabulous Figs

This is another in a sporadic series on my favourite tree groups, triggered perhaps by seeing the beautiful  Desert Figs growing on rock faces in the central desert ranges recently.
Desert, or Rock Fig Ficus brachypoda (formerly known as F. platypoda), John Hayes Rockhole, East MacDonnell Ranges, central Australia.
This species also grows in wetter tropical areas to the north, but survives in the relatively humid situations
of the desert ranges.
Desert Figs often grow in apparently impossible situations, sending roots down for metres
from where the seed lodged to find soil and eventually a water table. This distorted tree
is at Ellery Creek Big Hole, West MacDonnell Ranges.
This stunted specimen has sent roots out, mostly in vain, searching for sustenance.
Kings Canyon Rim Walk, George Gill Range.
And this one is in an even more exposed situation, surviving somehow in sand on top of the plateau
above Palm Valley.
This is just one species - and in terms of habitat an atypical one - among some 900 Ficus species, found throughout the world's tropics. This makes it one of the largest plant genera in the world and it is an ancient one, hence its very wide distribution. One characteristic is the milky latex, which in Ficus elastica produces a rubber (though this is not the Rubber Tree Hevea brasiliensis, from Brazil).

Another is the fruit, which apparently led figs (specifically Ficus carica) to be the first cultivated plant, known from sub-fossils of sterile figs (which could only have been produced by cultivation) from 11,000 years ago in what is now Palestine. 
Desert Fig fruits, Kings Canyon, George Gill Range, central Australia.
These fruits are not what they seem; in fact they are a cluster of numerous tiny fruits, enclosed, like the flowers from which they form, on the inside of the 'fruit'.
Fallen fig 'fruit' - the actual tiny fruits and flowers are visible on the inside of the casing,
which is comprised of the fused stems of the fruit.
The pollinating wasps hatch inside the infructescence - to give it its formal name - and feed on special infertile flowers before mating. The males die, never seeing the world outside their fig. As the females leave they collect pollen from the male flowers near the entrance, and take it to another fig which they pollinate while laying their eggs. It's up to you if you want to think about that when you next bite into one...

Many fig plants, including the Desert Fig, belong to a fig group called Banyans, or Strangler Figs. Stranglers are mostly rainforest figs which start life when a fruit is deposited by bird or fruit bat on a tree branch or rock face high above the ground, then sends down roots to find ground. They are not parasites, but will eventually kill the host tree, not by 'strangling' but by shading out its canopy, denying it essential sunlight. 
This Small-leafed Strangler Fig Ficus obliqua still contains the trunk of its host tree,
clearly visible through the root network.
Chichester State Forest, New South Wales.
More Small-leafed Stranglers from Chichester State Forest (above and below).
They have become huge dominant trees in their own right, with their own massive crown and load of epiphytes, especially (in the photo above) Birds Nest Ferns Asplenium sp.

Eventually all trace of the doomed host tree disappears, as its trunk rots and the fig 'fills in' the gap.
Small-leafed Strangler Fig buttresses, enclosed now so that the host is completely gone.
These aerial roots can become massive if they simply descend vertically without following the host's trunk. One of the most famous such trees is the Curtain Fig Ficus virens near Yungaburra on the Atherton Tableland, tropical Queensland.
Curtain Fig; the remarkable curtain formed when the host tree toppled sideways to lean against a neighbouring tree.
The fig went with it, putting down roots to the ground from all along its angled trunk
and eventually taking over the new host.
In some banyans these aerial roots provide props which allow the tree to spread out to cover vast areas. One specimen of the Indian Banyan Tree Ficus benghalensis was recorded as growing on a palm tree in the Kolkata Botanic Gardens in 1786. By 1911 the palm had long gone and the banyan covered nearly a hectare, supported by over 500 trunks.
Roots becoming supporting trunks, Moreton Bay Figs or Banyans Ficus macrophylla, Lord Howe Island.

So far all the illustrations are of Australian figs, but as I mentioned there are species throughout the tropics.
Figs and Euphorbias dominating woodland east of Masindi, Uganda.

Fig fruit, Inca Track above Machu Picchu, Peru.
Almost wherever you are reading this there are likely to be figs, either natural or cultivated. They deserve our unreserved appreciation.



Flabmeister said...

A thought provoking post as always. A couple of questions.
What is a sub fossil? My guess is something that has got some mineralisation but hasn't yet turned completely into rock.
You (and many others) describe the aerial roots of the Banyan as 'trunks'. From the depths of my brain, and A-level botany 50 years ago, I recall that the arrangement of tissues (xylem, phloem etc) is rather different in in trunks and roots, and wonder which model is found in the supporting structures of the Banyan?


Ian Fraser said...

Hi there and thanks for that. Firstly, subfossils - you're right. They comprise old (but usually not 'very old') organic material which hasn't had time to fossilise, or which has been preserved in the absence of appropriate conditions for fossilisation. I imagine that the subfossil figs were dried, enabling ready DNA extraction.
I'll need to delve further into the other, but my memory is that the xylem and phloem are continuous from root to trunk to branches to leaves. On the face of it it seems reasonable, given that water and dissolved nutrient has to flow from roots to the rest of the plant - but as I say, I should check that.

Flabmeister said...

Your comment has caused me to look into a few things about the structure of stems and roots. http://www2.estrellamountain.edu/faculty/farabee/BIOBK/biobookplantanatii.html has some pictures which illustrate the differing structure for small stems and roots. What I haven't been able to find anywhere is a cross section of a secondary root structure such as the aerial roots of a Banyan.