Monthly archives of “October 2014

Fossil palm from New Zealand Miocene
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The Fossil Palm Swamps of Central Otago, New Zealand

One of the endearing memories I have during my PhD was working on the banks above the Kawarau River near Cromwell (Central Otago, New Zealand), in the middle of the winter. I was belting my way with a pick into a sequence of mud that was frozen solid. This was probably a good thing, as it would have been a quagmire otherwise. But what I was digging out were fossil palms – criss-crossing palm fronds, layers of seeds, and even some flower-heads (Pole 1993, and see the featured image above). The area was clearly a palm-dominated swamp at the time (around 17 million years ago, Miocene period). Mud and lignite at the Kawarau River is full of palm pollen and probably correlates with similar layers tens of kilometres away at places like Clyde,  St Bathans, and even Te Anau and the Waitaki River. Clearly these palm swamps may have been huge. The palm fossils I was digging out were not a new discovery – one of the earliest students of New Zealand plant fossils, Baron von Ettingshausen, published a fragment of fossil palm frond in 1887. It probably came from the Kawarau River locality.

The original Ettingshausen palm fossil, now in the Otago Museum, New Zealand

The original Ettingshausen palm fossil, now in the Otago Museum.

Central Otago has the most extreme, ‘continental’ climate of the otherwise mainly maritime New Zealand. The summers are blistering hot and dry (In Alexandra the mean is about 10.8 C, the maximum recorded is 37.2 C) but the winters can be brutal. They aren’t quite on the scale of Mongolia or Canada, though once in a while we make a respectable effort. I remember waiting for the school bus in ground frosts down to -13C or so, but the official Alexandra minimum is -11.7 C. Not far away is the village of Ophir with New Zealand’s officially coldest temperature of -21.6 C. But mainly the winters are more just … miserable. During high school and early university I pruned fruit trees in early mornings when every step of tender frozen feet on rock-hard ground was an agony. But when the sun came up – so would the mist. The temperature would rise to about zero, but the ice in the trees, and the ground, would melt, freeze again, and melt, throughout the day. Boots would get wet and near frozen water would dribble up my sleeves. The mist could last for days, or even weeks. Central Otago is emphatically not palm climate. So what goes with the palm fossils?

Clearly things were a bit warmer, but what does that really mean? Was the average mean annual temperature higher? Or was it just that there weren’t cold winters? New Zealand does have the most southerly natural palms in the world – the limit is near Christchurch, not that far from the fossils, so on palms alone the mean temperature of Central Otago need not have been that different from the coast of the central South Island now. The winters were certainly not as cold as they are now – the natural distribution of palms is limited very clearly by the temperature of the coldest month reaching freezing. However, there were almost certainly more than one species of palm in Central Otago, perhaps two or three. This suggests that warmth was well above the limit for palms.

The broader questions that are raised by palm fossils in unexpected places are not trivial. On a larger scale than New Zealand, the presence of palm fossils in the continental parts of North America has been highlighted (Wing and Greenwood 1993). The palms require that conditions had to much more ‘equable’ than they are today. The ‘problem’ was that climate models of the time could not recreate these conditions (Sloan and Barron 1990). Climate models are a distillation of what we know about the physical processes that operate on Earth. When instances are found where the models ‘fail’, climate modellers have their work cut-out to isolate what it is they are missing. Carbon dioxide levels seem to be part, but not all of, the solution (Huber & Caballero, 2011). It’s an excellent example of progress in science, and of course – the relevance of studying plant fossils to the bigger picture.

But temperature is not everything. I find it interesting is that extensive palm swamps today tend to be correlated with distinct seasonality of rainfall – that is, there is a wet and dry season. The “dry” may not mean “drought”, but it might be the difference between water in the swamp being at the surface for part of the year, and being flooded the rest (Pole 2003, 2014). So palms may be giving us an important clue to atmospheric dynamics.

As well as this –the mud around the palm fossils has abundant fine charcoal, implying fire. Palms and fire may strike a kiwi as a bit odd. It wasn’t til I travelled in monsoonal northern Australia and saw a lot of palms in frequently burnt country that it sank in that palms are very fire resistant (and very flammable – recently my guides in the Indonesian forest would delight in putting a match to a palm tree when I wasn’t looking). So Central Otago may have been closer to the highly seasonal, often-burning, ‘fire-forests” of some parts of Australia than more typical rainforests.

Alas, you can no-longer visit the Kawarau River palm-fossil locality in mid-winter and pretend you are in a subtropical paradise. It sits below the waters of hydro-Lake Dunstan.

References

Ettingshausen, C. v. 1887: Beitrage zur Kenntniss der Fossilen Flora Neuseelands. Denkschriften der Akademie der Wissenschaften, Wien 53: 143-194.

Huber, M. & Caballero, R. 2011: The early Eocene equable climate problem revisited. Climate of the Past 7: 603–633.

Pole, M. S. 1993: Early Miocene flora of the Manuherikia Group, New Zealand. 4. Palm remains. Journal of the Royal Society of New Zealand 23: 283-288.

Pole, M. S. 2003: New Zealand climate in the Neogene and implications for global atmospheric circulation. Palaeogeography, Palaeoclimatology, Palaeoecology 193: 269-284.

Pole, M. 2014: The Miocene climate in New Zealand: Estimates from paleobotanical data. Palaeontologia Electronica 17(Issue 2;27A): 1-79, palaeo-electronica.org/content/2014/780-miocene-climate-of-new-zealand.

Sloan, L. C. & Barron, E. J. 1990: “Equable” climates during Earth history? Geology 18: 489–492.

Wing, S. L. & Greenwood, D. R. 1993: Fossils and fossil climate: The case for equable continental interiors in the Eocene. Philosophical Transactions: Biological Sciences 341: 243-252.

Fossil palm from New Zealand Miocene
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The Fossil Palm Swamps of Central Otago, New Zealand

One of the endearing memories I have during my PhD was working on the banks above the Kawarau River near Cromwell (Central Otago, New Zealand), in the middle of the winter. I was belting my way with a pick into a sequence of mud that was frozen solid. This was probably a good thing, as it would have been a quagmire otherwise. But what I was digging out were fossil palms – criss-crossing palm fronds, layers of seeds, and even some flower-heads (Pole 1993, and see the featured image above). The area was clearly a palm-dominated swamp at the time (around 17 million years ago, Miocene period; Mildenhall, 1989). Mud and lignite at the Kawarau River is full of palm pollen and probably correlates with similar layers tens of kilometres away at places like Clyde,  St Bathans, and even Te Anau and the Waitaki River. Clearly these palm swamps may have been huge. The palm fossils I was digging out were not a new discovery – one of the earliest students of New Zealand plant fossils, Baron von Ettingshausen, published a fragment of fossil palm frond in 1887. It probably came from the Kawarau River locality.

The original Ettingshausen palm fossil, now in the Otago Museum, New Zealand

The original Ettingshausen palm fossil, now in the Otago Museum.

Central Otago has the most extreme, ‘continental’ climate of the otherwise mainly maritime New Zealand. The summers are blistering hot and dry (In Alexandra the mean is about 10.8 C, the maximum recorded is 37.2 C) but the winters can be brutal. They aren’t quite on the scale of Mongolia or Canada, though once in a while we make a respectable effort. I remember waiting for the school bus in ground frosts down to -13C or so, but the official Alexandra minimum is -11.7 C. Not far away is the village of Ophir with New Zealand’s officially coldest temperature of -21.6 C. But mainly the winters are more just … miserable. During high school and early university I pruned fruit trees in early mornings when every step of tender frozen feet on rock-hard ground was an agony. But when the sun came up – so would the mist. The temperature would rise to about zero, but the ice in the trees, and the ground, would melt, freeze again, and melt, throughout the day. Boots would get wet and near frozen water would dribble up my sleeves. The mist could last for days, or even weeks. Central Otago is emphatically not palm climate. So what goes with the palm fossils?

Clearly things were a bit warmer, but what does that really mean? Was the average mean annual temperature higher? Or was it just that there weren’t cold winters? New Zealand does have the most southerly natural palms in the world – the limit is near Christchurch, not that far from the fossils, so on palms alone the mean temperature of Central Otago need not have been that different from the coast of the central South Island now. The winters were certainly not as cold as they are now – the natural distribution of palms is limited very clearly by the temperature of the coldest month reaching freezing. However, there were almost certainly more than one species of palm in Central Otago, perhaps two or three. This suggests that warmth was well above the limit for palms.

The broader questions that are raised by palm fossils in unexpected places are not trivial. On a larger scale than New Zealand, the presence of palm fossils in the continental parts of North America has been highlighted (Wing and Greenwood 1993). The palms require that conditions had to much more ‘equable’ than they are today. The ‘problem’ was that climate models of the time could not recreate these conditions (Sloan and Barron 1990). Climate models are a distillation of what we know about the physical processes that operate on Earth. When instances are found where the models ‘fail’, climate modellers have their work cut-out to isolate what it is they are missing. Carbon dioxide levels seem to be part, but not all of, the solution (Huber & Caballero, 2011). It’s an excellent example of progress in science, and of course – the relevance of studying plant fossils to the bigger picture.

But temperature is not everything. I find it interesting is that extensive palm swamps today tend to be correlated with distinct seasonality of rainfall – that is, there is a wet and dry season. The “dry” may not mean “drought”, but it might be the difference between water in the swamp being at the surface for part of the year, and being flooded the rest (Pole 2003, 2014). So palms may be giving us an important clue to atmospheric dynamics.

As well as this –the mud around the palm fossils has abundant fine charcoal, implying fire. Palms and fire may strike a kiwi as a bit odd. It wasn’t til I travelled in monsoonal northern Australia and saw a lot of palms in frequently burnt country that it sank in that palms are very fire resistant (and very flammable – recently my guides in the Indonesian forest would delight in putting a match to a palm tree when I wasn’t looking). So Central Otago may have been closer to the highly seasonal, often-burning, ‘fire-forests” of some parts of Australia than more typical rainforests.

Alas, you can no-longer visit the Kawarau River palm-fossil locality in mid-winter and pretend you are in a subtropical paradise. It sits below the waters of hydro-Lake Dunstan.

References

Links will take you to a downloadable pdf.

Ettingshausen, C. v. 1887: Beitrage zur Kenntniss der Fossilen Flora Neuseelands. Denkschriften der Akademie der Wissenschaften, Wien 53: 143-194.

Huber, M. & Caballero, R. 2011: The early Eocene equable climate problem revisited. Climate of the Past 7: 603–633.

Mildenhall, D.C., 1989. Summary of the age and paleoecology of the Miocene Manuherikia Group, Central Otago, New Zealand. Journal of the Royal Society of New Zealand 19, 19-29.

Pole, M. S. 1993: Early Miocene flora of the Manuherikia Group, New Zealand. 4. Palm remains. Journal of the Royal Society of New Zealand 23: 283-288.

Pole, M. S. 2003: New Zealand climate in the Neogene and implications for global atmospheric circulation. Palaeogeography, Palaeoclimatology, Palaeoecology 193: 269-284.

Pole, M. 2014: The Miocene climate in New Zealand: Estimates from paleobotanical data. Palaeontologia Electronica 17(Issue 2;27A): 1-79, palaeo-electronica.org/content/2014/780-miocene-climate-of-new-zealand.

Sloan, L. C. & Barron, E. J. 1990: “Equable” climates during Earth history? Geology 18: 489–492.

Wing, S. L. & Greenwood, D. R. 1993: Fossils and fossil climate: The case for equable continental interiors in the Eocene. Philosophical Transactions: Biological Sciences 341: 243-252.

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New Zealand – Beeches Invade Paradise!

In the old days in New Zealand, you needed to add the right prefix to telephone numbers to ring the adjacent villages. Our number was a 3-digit figure in the Clyde exchange. To ring Alexandra, 6 km down the road, I think we had to prefix their 4-digit numbers with a 1. To get us, they added a 2. To ring Omakau, about 15 km away, we had to prefix their number with a 3. Anything further than about that – you had to call an operator and get manually connected. I still remember my Mum muttering after the reaction she got when she rang the operator and asked to be  “connected with Paradise.” Apart from New Zealand in general, yes, there is a place called “Paradise”. It’s a large farming property beyond Glenorchy at the head of Lake Wakatipu. If offered (and still does) cabin accommodation in forested surrounds. Our family went there for a few days holiday.

Beech (Nothofagus) forest beside the road to Paradise, New Zealand. The openness here will be partly due to grazing.

Beech (Nothofagus) forest beside the road to Paradise. The openness here will be partly due to grazing.

I took some of my earliest photographs there – trying to catch the yellow-breasted robins on a box-Brownie camera that took 120 roll film. The forest at Paradise is prime habitat for them – it’s beech (Nothofagus) forest.  At about 10 years of age, my experience at Paradise was formative in what I thought a beech forest should look like. At least in the lower, flatter areas, it’s as close to some of those ‘mystical’ forests you see in fantasy images, as you can get (The ubiquitous ‘Lord of the Rings’ filmed Lothlorien near here). Virtually all of the canopy trees are beeches – and they can be very large – the big ones are probably 300-400 years old, and under the canopy its relatively open, you can walk around pretty freely. It’s a natural, promordial forest. And yet….

Spot the yellow-breasted robin! Shot with a box-Brownie camera in about 1970.

Spot the yellow-breasted robin! Shot with a box-Brownie camera in about 1970.

It’s self-evident that much of New Zealand could not have had forests, or any vegetation at all, at the height of the last ice age. That’s because the place was under hundreds of meters of glacier. This applies to Paradise which was underneath the glacier that formed Lake Wakatipu. It was only after the ice melted, around 11,000 years ago, and fresh rock was exposed, that plants could establish. The first plants would have been those grasses and shrubs that could deal with bare rocks – and the still harsh climate with a glacier not far away. Only after these smaller plants had gained a bridgehead could the forest come. The Paradise beech forest looks primordial- but its actually a new-comer.

The road through Paradise, New Zealand. Beech forest covers the glaciated mountains in the distance.

The road through Paradise. Beech forest covers the glaciated mountains in the distance.

The evidence of fossil pollen has shown that Nothofagus-beeches ‘invaded’ many of the valleys of the South Island relatively lately. In the Paradise region, this happened around 2000-1500 years ago (McGlone et al. 2003). So that’s an awfully-long time that the place had some sort of forest, but didn’t have beeches at all. The trigger was probably some sort of climate change. What unsettles me the most about this is that it wasn’t simply an ‘invasion’, as in beeches sort of filtering in and finding their niche, but a kind of genocide. When the beeches came, they took over. The pollen evidence suggests that much of what Nothofagus blitzed was a conifer forest, probably a fairly low one of celery pine (Phyllocladus) and bog pine (Halocarpus). You can still see patches of celery pine in what are probably fairly frosty open-patches in the beech forest. Totara is scattered through the forest today and may have been more prevalent before the beeches. But on the better soils of the valleys, I wonder if taller conifers, like matai and kahikatea were also common. If they were, then ‘genocide’ seems an even more appropriate term, as these species have been virtually extinguished from the area.

A frosty opening in the beech forest with smaller, yellowish celery pines (Phyllocladus). The taller, darker beech (Nothofagus) are in the background.

A frosty opening in the beech forest with smaller, yellowish celery pines (Phyllocladus). The taller, darker beech (Nothofagus) are in the background.

The implications are rather profound – far more than beeches simply ‘invading’. There was certainly a structural change in the vegetation – that a lower, more heterogeneous canopy of celery and bog pine was replaced by a higher and more even canopy of beeches seems certain. But if there were taller confers, then perhaps the plants that usually go with them, like tree ferns and supplejack vines, were also there. While a change from a low conifer forest to a tall beech forest could be seen as something of a ‘progression’, the change from a diverse, complex (some would say ‘tropical’) rainforest to an almost monospecific beech forest (that some would say was not a rainforest) seems more like a step backwards – a regression.

I wonder what kind of bird I would have tried to photograph if the beeches hadn’t invaded? Yellow-breasted robins are not restricted to beech forests (as far as I know), but they are said to prefer “structurally simple forests with dense, even canopies, and ground covered with leaf litter” (Borkin et al. 2008). That about sums up beech forests, chances are, the robins were not at Paradise before the beeches.

References

Borkin, Kerry M. et al (2008): South Island robin (Petroica australis australis) abundance and leaf-litter invertebrates in plantation and native forest.Notornis 54 (2): 65.

McGlone, M. S., Wardle, P. & Worthy, T. H. 2003: Environmental change since the last glaciation. In. Darby, J., Fordyce, R. E., Mark, A., Probert, K. and Townsend, C.  (Eds)  The Natural History of Southern New Zealand. Environmental change since the last glaciation, Otago University Press in association with the Otago Museum.: 108-127.

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Tropical Rainforest in …. South Westland?

At Ship Creek, just a few kilometers north of Haast, in South Westland, New Zealand, there is a wonderful boardwalk though an original swamp forest. The key tree is kahikatea (Dacrycarpus) and the  walk features a nice specimen of that species. There used to be a sign next to it describing it as a ‘dinosaur tree’ with a history back to the time of the dinosaurs. That’s debatable, but I see the sign has now been replaced. A comment on its history is now a little more circumspect, but there is something new:  Ship Creek is a “tropical rainforest”.

Swamp forest at Ship Ck, Westland, New Zealand

Huh? I’m sure the good folks of Haast would be bemused to hear their environment described as “tropical”. The place has an average annual temperature of about 11.3 C, although frosts are rare and light. However, I suspect “tropical” in this case refers to the structure of the forest, not the climate.

Ship Ck boardwalk, Westland, New Zealand

The arguments for this are best developed by J.W. Dawson, but the basic notion goes back to Cockayne (1926), who decribed New Zealand’s lowland forests as “subtropical”. Central to Dawson’s viewpoint was that vegetation types at a world-level be based on structure, not floristics or climate. Dawson (1962) explained that structurally, New Zealands lowland forests have several elements that are in common with tropical rainforests. These are things such as being multi-stratal (several layers of plants) and an abundance of lianes and shubby epiphytes. Some authors also note the abundance of tree ferns. Dawson made a point of distinguishing New Zealand’s Nothofagus forests from the lowland ‘tropical rainforests’. He saw the Nothofagus forests as being more closely related to the temperate deciduous forests of the Northern Hemisphere.  Nothofagus forests, at least the relative pure ones, have a notable lack of epiphytes and tree ferns and a very even canopy.

Dawson concluded that the “New Zealand lowland forest is closely related to tropical rain forest” and that the “use of the term ‘subtropical’ for this [lowland] forest is justifiable”, largely on floristic grounds, despite the confusion with geographic and climatic usage. He made the good point that “unlike the tropical zone the subtropical zone is not geographically defined”. Technically New Zealand is ‘subtropical’, but most people would not apply the term that way. Dawson added that he hoped a “botanist with a knowledge of all types of world vegetation” would come up with a classification “based on the nature of the vegetation itself”.  In fact, a few years earlier, the Australian botanist, L.J. Webb, who certainly would not have claimed that breadth of experience, but who did know Australian forests, had already attempted a classification based on their own features, and which dropped the tropical/subtropical/temperate terms (Webb 1959).

The theme of New Zealand forest classification was again taken up by Dawson & Sneddon (1969). The conclusion was “Ecologically, the New Zealand rain forest is comparable to lowland tropical rain forest in stratification and in range of special growth forms”. However, in this paper, the concept of “subtropical” was dropped, never to be mentioned once.

The swamp forest at Ship Creek has the typical ‘structural’ features that link it with more tropical forests. You can see plenty of lianes, epiphytes and tree ferns. It occurs in the ‘beech-gap’, meaning there are no Nothofagus trees. So is Ship Creek “tropical rainforest”? Yes, but from a tropico-centric point of view where tropical rainforests are seen as a kind of norm. Or we could make the leap and ignore both geographical confusing terms as well as ‘rainforest’. Under Webb’s (1959) classification, New Zealand lowland forests would probably be called “notophyllous vine forests” or “microphyllous vine forests” (in my opinion, much of what have been routinely called notophyll forests in Australia, are actually microphyll). But perhaps the more interesting question is not why New Zealand lowland forest ‘looks like’ tropical forest (why shouldn’t it?), but why pure Nothofagus forest (which surely boils down to the Nothofagus trees themselves) tend not to develop epiphytes and lianes and have tree ferns (dryness, surely).

Ship Ck-88634

Don’t let any of these semantics put you off the highly recommended Ship Creek boardwalk. It will only take 20 minutes from the car park, the path is almost flat, surfaced to about 1.5 m wide, and just in case visitors need to walk six abreast, the vegetation has been trimmed a further half meter or so either side.

References

Cockayne, L., 1926. Monograph on the New Zealand Beech Forests. Part 1. N.Z. State Forest Serv. Bull. 4.

Dawson, J. W. 1962: The New Zealand Lowland Podocarp Forest. Is it Subtropical? Tuatara 9: 98-116.

Dawson, J. W. & Sneddon, B. V. 1969: The New Zealand rain forest: A comparison with tropical rain forest. Pacific Science 23: 131-47.

Webb, L. J. 1959: A physiognomic classification of Australian rainforests. Journal of Ecology 47: 551-70.

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Australia’s Fatal Fire-Flume

The first time I came to Brisbane in the hot part of the year – I couldn’t believe how anyone could survive there. The nights were oppressively, putridly hot, and full of bitey-insects. Then I ended up living there and suffered for years. I would cocoon myself in a mosquito net, and poke a fan through the gap. Trouble with that was the fan just spun – without being able to draw any air. It was ages before I made the conceptual leap – do away with the mosquito net. A fan will keep both the insects and the heat away.

Actually, Brisbane doesn’t get that hot – it’s cities further to the south, like Melbourne and Sydney, that get the really, really hot days. And the killer-fires. In Brisbane, what makes the difference is the humidity. Why should this be? One might think that the further north one goes, things ought to warm up. in general this is true- but as is often the case, its the extremes that get you. And those extremes happen in the south-east.

It all comes down to the broader distribution of vegetation and a particular weather pattern. The most basic vegetation types – desert shrubland, woodland, forest, relate to overall rainfall (seasonality of rainfall is also important, but I’m keeping things simple). That is the amount of rain that occurs over a year or so. This is relatively high in southern regions, where polar fronts repeatedly pass through, in the north, where monsoonal rain and cyclones occur. The east coast is somewhere in between, as trade winds blow moisture across the land from the sea. The deserts are typically in central regions, away from a source of rain, and at latitudes where the high pressure cells remain for much of the year.

If you keep an eye on the weather maps in late spring/summer, you’ll notice that eventually a low pressure zone (a big L on the map) will appear – generally in the NW of Australia. This is a heat-low. Its a sign that the land is getting really hot. Some days at the height of summer, the whole of Australia can even become one big “L”. When that low starts to appear in the NW, watch for the climate scenario in the following diagram.

A typical 'fire-flume' climate scenario. A heat low in the north-west indicates Australia is heating up. A high pressure cell centred off the east coast is directing hot winds across the Eucalyptus forests of the south-eastern corner. Fires have broken out (crowny-things), and a polar front is approaching which will make things worse by creating gale-force winds.

A typical ‘fire-flume’ climate scenario. A heat low in the north-west indicates Australia is heating up. A high pressure cell centred off the east coast is directing hot winds across the Eucalyptus forests of the south-eastern corner. Fires have broken out (crowny-things), and a polar front is approaching which will make things worse by creating gale-force winds.

A high pressure cell centres itself just off the east coast. High pressure cells are bodies of descending dry air – and wind in these systems blows counter-clockwise (in the Southern Hemisphere). This means that in the northern sector, the trade winds can pick up moisture over a long traverse of the ocean – and plaster it against the northern Queensland coast. The Great Escarpment/Dividing range stops moisture from going much further inland, and makes the Cairns area and adjacent mountains, very wet.

Central Australian desert - hot, dry, but not much vegetation to carry a fire. Simpson Desert

Central Australian desert – hot, dry, but not much vegetation to carry a fire.

Eucalyptus forest in the hills above Melbourne. It's over-all wet (spot the tree-ferns), but on a hot, dry day, extremely flammable.

Eucalyptus forest in the hills above Melbourne. It’s over-all wet (spot the tree-ferns), but on a hot, dry day, extremely flammable.

Now consider the western sector of the High. Dry air descends here over a desert. Its not hot enough here to form a heat low – but it’s still damned hot, and there is no sea or lake for the air to pick up moisture. The air can travel across the desert getting hotter and hotter, but there isn’t much to burn there. But them it reaches the SE corner of Australia. It’s in this overall moist area that Australia’s really big forests of Eucalyptus grow.  So you have stinking hot, dry winds blowing out of the hot centre – almost directly onto highly flammable Eucalyptus forest. When this scenario happens, it’s only a matter of time before a fire breaks out. But another factor added to the mix, can make things far worse. A polar front moving into the area from the west, can turn a hot wind into a howling gale. This is when things get deadly. The danger area, roughly defined by Adelaide, Melbourne, Sydney and Hobart, is what Pyne (1998) has called the “Fire Flume”. The Eucalyptus burns – and stimulates more Eucalyptus to continue the cycle..

Keep watching the weather map, it’ll happen.

And Brisbane? It’s in a sort of betwixt and between location.  The amount and seasonality of rainfall there means that dense, tall Eucalyptus forest will not grow. So Brisbane is out of the ‘fire flume’. Being nearer the centre of the high pressure cell, it gets hold, but only gets sluggish winds. Unless an electrical storm forms along the Main Divide and then barrels across the lowlands to the coast, with enough rain to cool the place down for a day or two – it just stays hot and putrid

Reference

Pyne, S. 1998. Burning Bush – a fire history of Australia. Weyerhaeuser-Environmental.

Fossil Ripogonum from New Zealand Miocene
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Supplejack – a survivor from the Miocene in New Zealand

The first time I ever slept-out (sleeping bag, no tent), I was about four years old, and the place was an idyllic spot on the banks of Pipson Creek, just outside of Makarora. Its on the road to the West Coast from Wanaka/Hawea. One of my memories of that family holiday was swinging on a vine – I gracefully arched out before disappearing into a patch of bushes. The plant I was riding would have been ‘supplejack’ – Ripogonum scandens. As a budding young Tarzan or George of the Jungle, I was too young to know that vines don’t hang-down like they do in the movies. They are rooted in the ground and grow up – like most other plants in the forest. To make them swingable, they have to be severed – very ecologically uncool. I swung no more vines in New Zealand – I remember being confused how I never found any more large enough to take me. Truth was, I grew, and supplejacks aren’t that thick.

It was another twenty years before supplejack reappeared on my radar. I did my Honours thesis then my PhD on plant fossils from a region not far from where I grew up in New Zealand. One of the plant-fossil rich beds from Bannockburn contained leaf fossils that, as far as I could tell, were the same as the living species, Ripogonum scandens. That in itself was not surprising – they are a common component in many New Zealand forests. But the plant fossils at Bannockburn are Early Miocene in age (about 20-17 million years), not hugely old in geological terms. When I started my studies at Bannockburn (1980s) the predominant mind-set at the time was that New Zealand was a sort of ‘museum’ of Gondwana. It broke away from Gondwana about 80 million years ago and developed in isolation ever since.

Ripogonum leaf fossil from the Miocene of Bannockburn, New Zealand.

Ripogonum leaf fossil from the Miocene of Bannockburn, New Zealand.

The study of fossil pollen had long made it clear that Miocene New Zealand had many types of plant that have vanished since (Mildenhall 1980). So I expected to find fossil leaves at Bannockburn that were ‘new’, what I didn’t expect was the general lack of the plants that are common in New Zealand today. Other than Ripogonum (Pole 1993a) there was Metrosideros (rata and pohutakawa, Pole 1993b). There were beeches (Nothofagus, Pole 1993c), although with much larger leaves than those of today – and that was about it. If New Zealand’s current flora has existed since Gondwana time – surely I should have found more sign of them than what I did?

It was the first alarm-bell going off in my head that New Zealand’s history was quite different than commonly thought, that rather than being a museum of Gondwana, much of New Zealand’s flora (and perhaps biota) had travelled across the seas since physical isolation (Pole 1993d, 1994).

The Bannockburn fossil started me ‘noticing’ supplejack, not just where it grew, but where it didn’t. It must have been 1989 or 1990 that I spent several days based in Haast on a botany field trip organised by Prof Allan Mark. Supplejack was very much on my mind at the time and when I wrote a little report of the trip (Pole 1990). What exactly is supplejack, and what does it mean when you find it as a fossil? It is a rainforest plant – certainly a very different environment from what is now at Bannockburn, though may extend to more open swamps. It is a sprawling, climbing plant, typically waiting for a tree-fall gap and latching on to the young plants struggling to fill that gap and carry it up to the canopy. It seems to like moist, alluvial soils, but I’m not sure if anyone has had a close look at its ecology. Oddly, it appears absent from the fossil leaf beds at St Bathans. That’s saying something – but what?!

And Pipson Creek? Sadly it is no longer the idyllic glade it once was. The creek has become another disaster zone on the road to the West Coast – a beautiful stream turned into a sterile boulder-run. Climate change? Heavier rain-falls? Whatever is causing it, unfortunately I think it will only get worse.

References

*Some of these are links that will take you to an Academia.edu page where you can download a pdf of the paper.

Mildenhall, D. C. 1980: New Zealand Late Cretaceous and Cenozoic plant biogeography: a contribution. Palaeogeography, Palaeoclimatology, Palaeoecology 31: 197-233.

Pole, M. 1990. A paleobotanist in South Westland. Unpublished notes.

Pole, M. S. 1993a: Early Miocene flora of the Manuherikia Group, New Zealand. 5. Smilacaceae, Polygonaceae, Elaeocarpaceae. Journal of the Royal Society of New Zealand 23: 289-302.

Pole, M. S. 1993b: Early Miocene floras of the Manuherikia Group, New Zealand. 7. Myrtaceae, including Eucalyptus. Journal of the Royal Society of New Zealand 23: 313-328.

Pole, M. S. 1993c: Early Miocene flora of the Manuherikia Group, New Zealand. 8. Nothofagus. Journal of the Royal Society of New Zealand 23: 329-344.

Pole, M. 1993d: Keeping in touch: vegetation prehistory on both sides of the Tasman. Australian Systematic Botany 6: 387-397.

Pole, M. 1994: The New Zealand flora – entirely long-distance dispersal? Journal of Biogeography 21: 625-635.