Our research focuses on the population dynamics of plants and how they are influenced by impacts of natural disturbances and global environmental change. We are particularly interested in the interactive effects of fire, grazing and drought in grasslands and woodlands in southern Australia, and how climate change, fragmentation and shrub encroachment affect ecosystems.

Monday, 16 May 2011

Observations as the starting point for understanding the ecology of species and ecosystems

Mountain Ash - the tallest flowering plant in the world;
some trees have been measured  as being up to 150 m tall, but sadly
logging and fire has removed these magnificent forest giants
(Photo: John Morgan)
David Ashton was a plant ecologist who is best known for his observations and experiments on the regeneration ecology of the world's tallest flowering plant (Eucalyptus regnans, Mountain Ash). He dedicated his entire working life (from his PhD studies right up till his death in 2005) to the dynamics of the Ash forests - a period spanning over 50 yrs. Most of what we know about this species, and the community it towered over, is due to Dave's committed study of this ecosystem - you can read a summary of this work in The Big Ash Forest - changes in one lifetime. Rarely has a scientific paper's title reflected the subject matter so well.

Dave was a mentor of mine and I once asked him what he thought made a good ecologist. In his gentle, penetrating way he responded:
"a tape measure, a spade, a good set of eyes, and an inquiring mind".

While the tape measure and spade are still very important components of the ecologists toolbox, and the toolbox might now include things like a GPS, a laptop computer, a digitial camera and dataloggers, etc, I think it is valuable to reflect on the last two points, for without them, all the technology doesn't really have a purpose.

All good ecology starts with observations. And careful ones at that. Having made some observations, it then requires the ecologist with a sharp mind to interpret what they have seen. Indeed, I often think of ecology as involving detective work, putting all the pieces of the puzzle together.

I'll give a recent example to illustrate the point.

I've just returned from the Otway Ranges where Phil Keane, Pete Green, David Cameron and I (along with a bunch of undergraduate students) have been observing the ecology of cool temperate rainforests. CTR are dominated by Nothofagus cunninghamii (Myrtle Beech), a tree with a Gondwanan origin. The genus Nothofagus occurs in New Zealand, in South America and, formerly, in Antarctica when it was ice-free, and provides evidence that the southern continents were once connected before continental drift led them to seperate and move far apart. Today, Nothofagus occurs in the Otways in the deepest of the moist gullies where fire is very rare. This part of the story is well-known.

Myrtle Beech in the Otways - dead trees are clearly visible
(Photo: John Morgan)
 One of the major causes of mortality of Nothofagus is the Myrtle Wilt, an air-borne fungal disease caused by the naturally occurring native pathgenic fungus Chalra australis. The fungus infects trees that have been wounded in the outer bark - perhaps by windstorm and falling branches. Following infection, 'wilting' of the canopy occurs; this is easy to observe because leaves first turn yellow, the tree dies, and then brown leaves shed over the following 18 months. This part of the story is well-known.

Or is it? While observing Nothofagus that were recently infected (evidenced by the yellowing of leaves) or had been infected some time ago (evidenced by brown leaves to completely defoliated canopies), we observed something that throws a spanner into this ecological story.

On one clearly infected tree, we noticed that nearer the base, new shoots with green leaves were growing quite vigorously. This is not supposed to happen. As David put it:
"Myrtle Wilt is a death sentance for a Myrtle Beech tree".

We then made a second and a third observation to the same effect. Hence, this is not an isolated occurrence. Perhaps Myrtle Wilt is not always fatal as it was once thought to be?

At another site in the rainforest, we observed very large trees that had been defoliated some time ago, presumably because of the fungus. There again was vigorous regrowth from the base, casting further uncertainty on the well-known "fact" that Myrtle Wilt always kills Myrtle Beech. Our observations have confused us - we are observing a phenomenon that is not supposed to occur. Perhaps the story is more complicated than was originally thought. Perhaps the disease is not always lethal. Perhaps there are circumstances where the tree can survive infection.

Of course we have a lot more work to do before we can definatively re-write the story here. But it demonstrates two things. By making observations of nature (and these are very simple observations) - do Nothofagus die or regrow after Myrtle Wilt - and thinking about what we are observing (i.e., the implications of these observations in light of current understanding), we have gained some rather profound insight into the ecology of this rainforest. This means sometimes questioning the accepted wisdom on the topic.

And we haven't yet got our technology out of its toolbox.

Secondly, it highlights that long-term observations of natural systems are crucial to understanding them and making correct decisions about their wise use and management. Dave Ashton knew this - he repeatedly tested ideas about the regeneration and succession of Ash forests over a lifetime. For most of us, we don't have a lifetime to answer the pressing questions such as climate change impacts on biodiversity. But we can gain such insights if we cleverly use revisitation studies and historical datasets (such as herbarium records & quadrat data), use chronosequences (space-for-time substitution), and establish permanent plots for monitoring with specific questions in mind.

I look forward to us further unravelling the Myrtle Wilt story, a story that was once thought written. In the meantime, we need to go off and make a few more observations!

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