Fire in Australian forests: The Phoenix from the ashes

The bushfires of the last week on the east coast, particularly those in Victoria, have been tragic and devastating. Loss of human life and property, as well as death and injury among the fauna of the burnt areas are tragic and immediately confronting.The landscape itself seems completely dead in much of the area affected by the fires.

But the native vegetation we have come to love in this country not only responds well to fires, but in the case of many plant species, relies on fire for survival. Although the trees look black and dead now, and the understorey is completely gone in some places, it will not take long before signs of life begin to emerge.

Underneath the bark of many large trees, Eucalypts in particular, but other species also, are dormant buds. These epicormic buds are not actively growing for most of the life of a tree, but in times of stress, for example, when the tree is defoliated by animals or fire, the epicormic buds spring to life, and grow leaves and small branches to provide energy to the roots of the tree. This is very important, as when tree roots die, they cannot support the canopy. This epicormic growth will allow for the surviving branches to re-grow all their foliage and re-establish themselves much faster than new seedlings are able.

Some trees, especially among the Eucalypts, also have lignotubers below the ground, the soil providing even further protection from heat of passing fires. These trees will sprout new major limbs and trunks from ground level, and multi-stemmed trees in the forest are often the result of such a fire response.

Of course not all trees will survive, but even the dead stags provide shelter for animals, from wood feeding insects, to larger creatures such as birds and mammals, who may also feed on the insects. These animals take some time to return to burnt out areas, and their numbers will be slow at first to increase, but neighbouring populations and survivors will eventually recolonise the fire stricken areas.

At the soil level, the ash bed after a fire provides a fertile nursery for seed germination, of understorey shrubs, herbs and grasses, as well as new trees. The so called "soil seed bank" is an accumulation of seeds dropped every year by most plants, which have not been given the appropriate conditions for germination. Warmth and moisture in just the right quantities will germinate most seeds, and the clearing of the overshadowing plant canopy enhances this. This includes thousands of Eucalypt species which will eventually fill in the gaps in the canopy left by the trees that do not survive.

But even more reliant on fire, are the Wattles. Most Acacia species have a very hard seed coat. While occasionally passing through an animals gut will break it down enough to allow it to germinate, more effective is the application of heat. A bushfire will weaken or crack the dormant wattle seeds in the soil, and allow them to begin growing. The importance of wattles as a "pioneer species" can not be underestimated. The roots of all wattles are covered in nodules, which provide habitat for Rhizobium bacteria. These bacteria suck nitrogen out of the air and fix it in a form that plants can use for their nutrition. After a fire, nitrogen levels may be significantly depleted, and the wattles help restore levels to a productive state. They also provide shelter from sun and evaporation that allow smaller species to re-establish beneath them, before dying in a relatively short period of usually 20-30 years.

Banksias also rely on the heat from fires to crack open their seed cases, famously characterised by May Gibbs as Banksia Men. The seeds are held tightly in woody follicles and only released when heat is applied, most naturally by fires. The flowers of these trees provide a nectar source for birds and insects, and even some tiny marsupials. Allocasuarina species, sometimes called native pines, retain their seeds cases, or cones, on the tree, often until fire events cause them to fall, where they open and deposit seeds on the ground for germination. These trees also fix nitrogen in the soil, and are another important pioneer species after fires.

While it may look at present like a desolate and barren landscape, invisible to our eyes, processes are already underway to restore the bush to its familiar beauty. A beauty that actually relies on this periodic ordeal. Rather than point fingers at forest management practices as scapegoats for these occurrences, it would be far more useful to spend time and energy minimising their impact on the people who live with the dangers of the Australian forest environment, and protecting human life from these essential, and inevitable fires.

Just the facts #4

Recently I was asked

Why are trees tall?

The simple answer to the question is

Because other trees are tall

but I think this deserves some qualification.

Most people are familiar with the theory of evolution by natural selection, in which the individuals most suited to their environment successfully produce more offspring than less suited individuals. The concept is most commonly reduced to a truism "Survival of the fittest", and is just as commonly misunderstood.

Many people have the idea that fitness means the strongest, fastest or largest individuals will be favoured in selection. This is obviously not the case, as there are far more species smaller than a tennis ball than larger. In fact, there are vastly more species of life on earth smaller than the eye can register than those we humans can view. So clearly bigger is not necessarily better when it comes to natural selection. Except when it is.

The fiercest competition for survival is not between species, for example the rabbit and the fox, or the antelope and the lion, but within species. Because each individual of a particular species is competing directly with every other member of their population for all resources: food, shelter, territory, mating partners, etc; the competition is far more direct and consequential than the occasional dodging of a potential predator.

This brings us back to the tall trees. In certain forest systems, trees tend to be taller, and with fewer low branches than where trees are spaced further apart by natural means (for example water availability) . The trees which germinate and grow tall the fastest are favoured, and contribute to the failure of their immediate competitors by blocking essential sunlight to slower growing trees of the same species.

This fast growth is influenced by environmental factors, such as rainfall, and physiological factors, such as the natural etiolation (or elongation, a process separate to actual growth) of stems in shade. But it is fundamentally coded for in the genes of the tree species. So, even when grown outside the forest, forest trees retain some of the height of their counterparts in natural environments. The genetic information of the species is known as the genotype,, and this, in combination with environmental factors, goes on to produce the final shape of the individual, referred to as the phenotype.

Growing species outside their natural environment does not always result in similar looking specimens, however. A famous example is the Lesser Flamingo (Phoenicopterus minor), the common, pink wading bird from the Rift Valley in Africa. In its natural environment, the bird feeds on a kind of algae or cyanobacteria which are metabolised by the birds, and give them their distinctive colour. removal of the natural food source of the bird results in their feathers fading to white over time. The genotype of the bird allows for their pink plumage, but the phenotype is influenced directly by environmental factors.

A century of destruction: the death of the Murray Darling basin

In the 1870s, Victoria's second largest Port was not where most would place it today if asked to pinpoint it on a map. It was not Geelong, or Portland, nor was it in the sheltered Westernport Bay, or Port Welshpool on the Gippsland coast. It was 96 metres above sea level, and over 200 kilometres to the nearest sea at Port Phillip Bay. It was Echuca, on the Murray River, where a fleet of over a hundred paddle steamers navigated the river on a daily basis transporting wool and other agricultural produce, as well as manufactured goods between inland towns along the Murray and Darling rivers, and many of their tributaries.

By the dawn of the 20th century, much of this transport load had moved on to the railways, and though it had begun in the 1880s, irrigation with water drawn from both these rivers began in earnest. This opened up huge areas of the inland to farming, particularly for water hungry crops, orchards, and vineyards. And the flow of the largest river system in the country was gradually, but consistently reduced to a trickle. The once navigable river has all but dried up, and in most summers would be difficult to travel along in more than a kayak.

The effect of this drastically reduced water flow on the natural environment has obviously been immeasurable. And now, it seems that concerned scientists have given the river less than six months to live, before it becomes little more than a drain, carrying the run-off effluent from the farms that have profited from it for over a century.

It seems almost incomprehensible that such a dramatic tragedy could take place before the eyes of a population so supposedly concerned with the environment. But there it is. For once, the government is faced with a decision which is as straight forward as it has always been, though in this case probably much more obvious: economy vs environment.

In this particular case, at this time, the choice is either/or. The time for compromise has clearly passed, and if the river is to be saved, then massive amounts of water need to be released from facilities upstream. This water will cost money, and in no way do I expect the farmers who rely on it will wish to go without compensation.

But the clock is audibly ticking, and a lack of decision will ultimately be the final nail in the coffin for this once mighty river system.

Just the facts #3

Today's questions:

What is the line between artificial and natural?

and, in relation to tomato sauce:

At what point does a tomato cease to be a fruit?

In response to the first question, i would contend that "artificial" means that it has been constructed or manufactured by human beings, while natural means it may be found already existing in nature without human interference. What this means in actual fact is really a question of context. For example, a food product may claim it contains "no artificial colours or flavours", but obviously, it may be coloured or flavoured with "natural" agents. The same goes for artificial sweeteners, preservatives, and so on.

In this context, it usually means the difference between a naturally occurring chemical, which is extracted directly from a plant or animal, and a synthetic chemical, which is obtained by chemical reaction in a laboratory or factory. There is no guarantee that a naturally occurring chemical is any safer than a synthetic one, and some of the most toxic substances known to science come directly from natural sources. In fact, in certain cases, synthetic versions of chemicals may be safer than their "natural" alternatives, having potentially toxic, carcinogenic or mutagenic compounds removed or converted into harmless forms.

As for the second question, this requires a brief foray into botanical terminology. In botanical terms, a fruit is the seed of a plant, together with the ripened ovary. So, a grain of wheat is a fruit, as is a coconut, and at least part of what we call a Tomato. The tomato is formed when the ovules in a tomato flower are fertilised by pollen. The ovules are contained within an ovary, which swells after fertilisation to become the flesh of the tomato fruit. However, tomato sauce is usually made with only the fleshy parts of a tomato, known as the carpel, excluding the seeds. So in my opinion, a tomato ceases to be a fruit when it is de-seeded, as the seed is the defining characteristic of a fruit.

However, while this is a botanical explanation of when a tomato ceases to be a fruit, legally, in the United States at least, it ceased to be a fruit in 1893, as a result of a court ruling on tariffs covering fruit and vegetables. According to the US supreme court, the tomato is a vegetable.

Cerebrity of the Week #1: Andrew Merchant

These days it seems that much of the media is saturated with "celebrity news". Reports of births, deaths, marriages, affairs, and general gossip about people who, were they not so spotlighted by the media, would be otherwise relatively unimportant to the world at large. Actors, musicians, models, and people who are just obscenely rich may have no actual influence on the lives of anyone but for media reports flooding our senses on a daily basis. That politicians and increasingly other actual professions are now compelled by necessity to "market" themselves, their ideas, or their organisations in order to "compete" for attention is somewhat disturbing.

So, in my own small way, I have decided to award a weekly prize to the person who I feel has the most to offer the world on account of who they are, what they think, and what they have achieved. It is the reverse of celebrity in a way, as these faces may not be known to the masses, but in their own way, they have contributed more to the world than all the hotel heiresses, former game show hosts, reformed child actors, celebrity brothel keepers and other miscellaneous media spakfilla combined.

This week, in order to highlight the cumbersome-but-descriptively named (the Department of Agriculture, Fisheries and Forestry don't like acronyms, because it makes them look daffy) Science and Innovation Awards for Young People in Agriculture, Fisheries and Forestry entries for which close on July 14th, I wanted to name one of last years winners as cerebrity of the week. Please, put your virtual hands together for Andrew Merchant!



Andrew's project involved trying to figure out what cellular processes allow Australian tree species greater tolerance of their harsh environmental conditions. He hopes to use this information in order to breed tougher trees, more capable of withstanding future climatic extremes, and current marginal environments.

Congratulations, Andrew, for being the Survival of the Fittest Cerebrity of the Week, Number 1.

The benefits of climate change?

I was reading the other day on Science Daily about the positive effect of climate change on the range and population of a species of butterfly in Great Britain, the Brown Argus (left). The article stated that the butterfly had increased it's range over the last thirty years much further north than it had been previously known, all the way into Scotland.

The article then went on to explain how this extension of range had allowed the caterpillars of the butterfly to escape their usual parasites, which were not present in the more northerly habitat. Now obviously for the Brown Argus butterfly, this is largely a beneficial outcome, and as the geographic shift was allowed by warmer temperatures, at least in part due to climate change then surely this is a "benefit of climate change"?

I can't say I agree with the assessment of Science Daily that "some species benefit". If all species are affected by climate change, the likelihood of predicting the ecological impact of the changes is minimal. In this case, for example, removal of the natural predators of the butterfly also removes the selection pressure on the butterfly to resist them. This means that if interbreeding occurs between individuals from the new range and those from the old, those in the old range have an increased risk of being less fit for their environment. This kind of genetic pollution is at least possible, and at worst could result in the species becoming endangered, or even extinct in it's original range.

More disturbing a prospect, though, is the effect of the caterpillars in their new environments. With no predation, caterpillar numbers could reach much larger numbers than in their old feeding grounds, and could have adverse effects on natural vegetation, or even agricultural crops. The caterpillars may out-compete the local species of larvae, which could lead to their predators being reduced in number. This in turn could lead to serious implications in boom and bust cycles of caterpillars, and their effects on local vegetation.

There is simply no way anyone can claim that an increase in population of any single species is a benefit, no matter what it's cause. All change may be either good or bad, but without appropriate analysis, there is no way to predict which.

Just the facts #2

Okay, so, in response to elaine's question from two days ago, when she asked

"can you please tell me if there are cells that do not contain DNA? If yes, please give me some examples. Also if yes, what is the difference between DNA-less cells and cells with DNA as it what do they do differently and why do some have it and some don't (if it is known)."

The short answer is yes... and no.

In mammals, the red blood cells contain no nucleus or organelles, so contain no DNA. Red Blood cells are primarily for carrying oxygen throughout the body, and removing carbon dioxide from tissues, and are specialised for this function by having little in the way of cellular "baggage" in order to optimise their efficiency for the task. This also ensures the cell itself uses none of the oxygen it carries. This means they are incapable of self repair or cell division. Red blood cells are constructed in specialised regions of an animal body, for example, in the bone marrow, or in the liver in embryos. They may be stored to some extent in the spleen for periods when rapid physical activity requires larger volumes of oxygen to be delivered rapidly to muscle tissues.


Human Red Blood Cells

In plant tissues, the xylem cells, those carrying water and nutrients from the roots to other tissues, completely lack a protoplast at maturity. They also contain no DNA, but are effectively non-living tissues, and comprise the woody parts of plants. Again, this is to increase the efficiency of their primary function, that of conducting water through the plant. They are also incapable of self repair or cell division as a result.

Bacteria contain DNA, but unlike the linear chromosomes of multi-cellular organisms, it is arranged in a ring like structure. Certain organelles of plants, such as chloroplasts; and animals, such as mitochondria; contain their own DNA. Because such organelles are usually inherited directly form the female parent, and because their rate of mutation is very low, this allows certain genetic testing to gauge the rate of evolution between different species.


Bacteria

Viruses are complex organic entities, and though not classified as living, may also contain DNA, or in some cases RNA. They differ from living organisms in that they lack the ability to reproduce on their own, and require a host in order to multiply. Viral infections cause the most trouble to other organisms when they reduce the rate of cellular processes by hijacking the machinery and energy of a cell to make copies of the virus.


An "artificial" bacteriophage virus (electron micrograph)