Spring is here and wattles are out in bloom: a love letter to our iconic flowers



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Gregory Moore, University of Melbourne

Spring has arrived, and all over the country the hills and riversides are burnished with the green and gold of Australian wattles, all belonging to the genus Acacia.

It’s a spectacular sight, but not a surprising one as there are about 1,000 Australian species in the Acacia genus ranging from very small shrubs to tall, longed-lived trees. They occur in ecosystems from the arid inland to the wet forests of the east coast.




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Wattles have been widely used by Indigenous people for millenia, and celebrated by “Wattle Day” on September 1 for more than a century.

But their lineage may be much older. Australian wattles have relatives in Africa, South America, India and parts of Southeast Asia. This distribution suggests the wattles may have originated in Gondwana before the super-continent fragmented about 180 million years ago.

So let’s take a closer look at what makes these iconic flowers so special.

Wattle on a cloudy day
Wattle can always brighten a dreary day.
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Don’t blame wattles for your hay fever

Not everyone welcomes the wattles’ golden blooms — many blame wattle pollen for their hay fever or asthma.

However, many species of wattle have aggregated pollen, which means it’s very heavy and tends to fall straight to ground. You have to be virtually under the plant for it to affect you.

They can cause trouble, but it’s more likely your allergy is due to some other inconspicuous plant, such as grass, that you haven’t noticed compared to the bright yellow of the wattles. It’s worth having an allergy test.




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While a majority of wattles flower in spring and summer, a significant group — such as the sunshine wattle (A. botrycephala), Gawler Range wattle (A. iteaphylla) and flax wattle (A linifolia) — flowers in autumn and winter. This can give the impression in some places that they’re flowering year-round.

What’s more, many species are hardy, and they can help in the process of taking nitrogen from the air and adding to the soil. That means they can be very handy in ancient, nutrient-poor Australian soils.

A mulga in the Australian desert
Mulga grows over about 20% of our continent.
Mark Marathon/Wikimedia, CC BY-SA

Many of the smaller shrub wattles may live for only a decade or so, but some, such as mulga (Acacia aneura) can live for centuries and are crucial to the viability and stability of arid inland ecosystems. They can have surprisingly large and deep root systems for such small shrubs or trees. This is to obtain water, but also binds the soil.

However, mulga-munching horses, cattle and other feral grazers threaten the persistence of mulga-dominated communities. If mulga and other inland Acacia species are lost, the soils can become loose and mobile, which results in stable productive land becoming desert.

By any other name

In the early 2000s, there was fierce debate among plant taxonomists about how closely the African and Australian species were related.

The name “Acacia” rightly belonged to the African group, but because there were so many Australian species that would need to be renamed, Australia was allowed to keep the name “Acacia” in 2011 — much to the chagrin of foreign taxonomists.

This resulted in the genus being divided. Australian wattles stayed as Acacia, but African wattles are now in the genera Vachellia or Senegalia, and those from the middle Americas (around Mexico) are Acaciella and Mariosousa.

The different names reflect long, separate histories and different ecological characteristics. (The name changes rankle still with taxonomists!)

Close-up of black wattle flowers
Black wattle is a pest overseas.
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There are also weedy wattles in Australia and elsewhere. Many of us know from hard experience that the splendid ornamental tree, Cootamundra wattle (Acacia baileyiana), can become a weed if it grows outside its very restricted natural range in New South Wales. And Australia’s black wattle (A. mearnsii) is a significant weed in other parts of the world.

It can come as a bit of a blow to know Australia’s floral emblem, golden wattle (A. pycnantha), can be weedy both at home and when it travels abroad (perhaps like some Australians).




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Interestingly, most of the Australian wattles lack thorns, unlike their relatives in Africa. In Africa, thorns protect the plants from large mammalian grazers such as giraffes.

Ants love wattles, too

If you don’t like ants, it might be worth checking which species of wattle you have in your backyard, or intend to buy.

Many wattles have a very special relationship with some insects. In Central America, ants penetrate the thorns of Bulls Horn wattle trees and establish their colonies. They then defend the tree against other insects, and if branches of another tree touch the host tree, the ants will cause such damage that the other tree will die back.

There are more than 1,000 species of wattle in the Acacia genus.
Shutterstock

In Australia, the relationship between ants and wattles is based on food. The hard wattle seeds have a tasty and oil-rich outgrowth called an “aril”, which is irresistible to some ant species.

The ants harvest the seeds and take them back to their nest, where they’re safe from other hungry grazers until it is damaged by fire or flood and the seeds germinate.




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Some wattles, the mulga among them, have little glands at the base of their phyllodes (the modified leaf stalks). These glands secrete a form of sugary syrup that attracts feeding ants. These ants may also protect host trees or perhaps leave the flowers alone to allow a greater seed set to grow.

It’s clear wattles have a lot going for them. They are diverse in number, habit, size, longevity and flowering season — there’s a wattle for every occasion. For all of these great traits, it’s still that green and gold that endears them to Australians.The Conversation

Gregory Moore, Doctor of Botany, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

The winter was dry, the spring will likely be dry – here’s why


Jonathan Pollock, Australian Bureau of Meteorology and Andrew B. Watkins, Australian Bureau of Meteorology

Winter still has a few days to run, but it’s highly likely to be one of Australia’s warmest and driest on record. While final numbers will be crunched once August ends, this winter will probably rank among the top ten warmest for daytime temperatures and the top ten driest for rainfall.

While it was drier than average across most of the country, it was especially dry across South Australia, New South Wales and southern Queensland. Small areas of South Australia and New South Wales are on track for their driest winter on record.




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In contrast, parts of southern Victoria, western Tasmania and central Queensland were wetter than usual.

Preliminary winter 2019 rainfall deciles.
Bureau of Meteorology

Thirsty ground

Soil moisture normally increases during winter (except in the tropics, where it’s the dry season), and while we saw that in parts of Victoria, for most of Queensland and New South Wales the soil moisture actually decreased.

Dry soils leading into winter have soaked up the rain that has fallen, resulting in limited runoff and inflows into the major water storages across the country.

A glass half empty

Sydney’s water storages dropping below 50% received considerable public attention, and unfortunately a number of other regional storages in New South Wales and the Murray Darling Basin are much lower than that.

The winter ‘filling’ season in the southern Murray Darling Basin has been drier than usual for the third year in a row, and storages in the northern Murray Darling basin are extremely low or empty with no meaningful inflows.

Some rain in the west

Some regions did receive enough rainfall to grow crops this cool season. However, northern New South Wales and southern Queensland didn’t see an improvement in their severe year-to-date rainfall deficiencies over winter.

In fact, the area of the country that is experiencing year-to-date rainfall in the lowest 5% of historical records expanded.

In better news, the severe year-to-date deficiencies across southwest Western Australia shrank during winter.

Indian Ocean Dipole the culprit

Sustained differences between sea surface temperatures in the tropical western and eastern Indian Ocean are known as the Indian Ocean Dipole (IOD). The IOD impacts Australian seasonal rainfall and temperature patterns, much like the more well known El Niño–Southern Oscillation.

Warm sea surface temperatures in the tropical western Indian Ocean and cool sea surface temperatures in the eastern Indian Ocean, along with changes in both cloud and wind patterns, have been consistent with a positive Indian Ocean Dipole since late May.

International climate models, some of which forecast the positive IOD as early as February, agree that it is likely to continue through spring.

Typically, this means below average rainfall and above average temperatures for much of central and southern Australia, which is consistent with the current rainfall and temperature outlook from the Bureau’s dynamical computer model. The positive IOD is likely to be the dominant climate driver for Australia during the next three months.

Comparison of international climate model forecasts of the IOD index for November 2019.
Models from the Australian Bureau of Meteorology, Canadian Meteorological Centre, European Centre for Medium-Range Weather Forecasts, Meteo France, National Aeronautics and Space Administration (USA) and the Met Office (UK)

A dry end to 2019 likely

Chances are the remainder of 2019 will be drier than normal for most of Australia. The exceptions are western Tasmania, southern Victoria and western WA, where chances of a wetter or drier than average end to the year are roughly equal.

The spring 2019 outlook showing low chances of above average rainfall for most of the country.
Bureau of Meteorology

Warmer than average days are very likely (chances above 80%) for most of the country except the far south of the mainland, and Tasmania.

Nights too are likely to be warmer than average for most of the country. However, much of Victoria and Tasmania, and southern parts of South Australia and New South Wales have close to an even chance for warmer than average minimum temperatures.

Due to the warm and dry start to the year, the east coast of Queensland, New South Wales, Victoria and Tasmania, as well as parts of southern Western Australia, face above normal fire potential this coming bushfire season.

More outlooks more often

The term weather describes conditions over shorter periods, such as from minutes to days, while the term climate describes the more slowly varying aspects of the atmosphere.

From today, the Bureau of Meteorology is closing the forecast gap between weather and climate information with the release of weekly and fortnightly climate outlooks.

For the first time, rainfall and temperature outlooks for the weeks directly after the 7-day forecast are available. One- and two-week outlooks have been added to complement the existing 1-month and 3-month outlooks.




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The new outlook information for the weeks ahead also features how much above or below average temperatures are likely to be, and the likelihood of different rainfall totals.

The Bureau’s outlook videos explain the long-range forecast for the coming months.
Bureau of Meteorology


You can find climate outlooks and summaries on the Bureau of Meteorology website here.The Conversation

Jonathan Pollock, Climatologist, Australian Bureau of Meteorology and Andrew B. Watkins, Manager of Long-range Forecast Services, Australian Bureau of Meteorology

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Not just heat: even our spring frosts can bear the fingerprint of climate change


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Frost affected many crops across WA during September 2016.
WA Department of Primary Industry and Regional Development

Pandora Hope, Australian Bureau of Meteorology; Andrew King, University of Melbourne; Eun-Pa Lim, Australian Bureau of Meteorology, and Michael Grose, CSIRO

In recent years, scientists have successfully identified the human fingerprint on hot years, heatwaves, and a range of other temperature extremes around the world. But as everyone knows, climate change affects more than just temperature.

The “signal” of human-induced climate change is not always clear in other weather events, such as cold snaps or episodes of extreme rainfall.

Three new studies, released today as part of a special edition of the Bulletin of the American Meteorological Society, take a closer look at two such events, both of which happened in southern Australia in mid-2016: the frosts that hit Western Australia’s South West, and the extremely wet weather that hit much of southeastern Australia during that year’s winter and early spring.

Perhaps surprisingly, WA’s frosts showed a fingerprint of climate change, due to changes in weather patterns. Meanwhile, there was very little climate change signal in the extreme rainfall that hit the southeast.


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While there is a clear human-driven upward trend in Australia’s average temperatures and the future of southern Australia is projected to be dry in the cool seasons, last year Australia experienced its wettest winter and September on record. Meanwhile, September in WA’s South West brought up to 18 frost nights across the region – the most on record in some locations.

An increasing temperature trend would limit the number of extreme cold events, and broadly speaking this is true for Australia. So what caused the record frost risk in South West WA in September 2016?

For the northern hemisphere, a “wobbly” jet stream has been proposed as the cause of periodic blasts of extreme cold weather. In this theory, human-driven changes to atmospheric circulation cause Arctic air to temporarily extend southwards over populated areas, bringing Arctic weather in spite of the background warming trend. But this kind of theory hasn’t been examined in depth for Australia.

During southwestern WA’s bout of September frosts, the atmospheric pressure was generally very high, and the skies were clear. What’s more, that month featured a particularly persistent weather pattern of slow-moving high pressure west of Australia, which brought in cold air from the south.

Persistent high pressure off the west coast brought cold, dry nights to WA’s southwest.
BoM, Author provided

The question is whether human-induced climate change is altering the circulation to make these conditions more likely. Research led by Michael Grose addressed this question by comparing climate models that describe the current, human-altered climate, and ones that leave out the influence of human-produced greenhouse gases.

Their results suggest that human-induced climate change is indeed changing the circulation patterns in our region, making this particular pattern more likely. They also suggest that it’s a fine balance between increasing average temperatures and these altered circulation patterns in this part of Australia.

In the models, daily minimum temperatures were not colder in the current climate than in those models without a human influence. This suggests that the two effects may cancel out (as far as extreme frost is concerned), although more work is needed to understand this intriguing possibility.

Record wet winter

Raising the global temperature can also make air more humid and therefore can result in more extreme rainfall events. The wettest day of the year is projected to become wetter by the end of the century. Are we already seeing an increase in extreme rain, and does it also hold true over the course of a month or a whole season?

September 2016 was by far the wettest September on record in Australia’s southeast, including the Murray Darling Basin, Australia’s food bowl. The amount of moisture in the air column during that month was extremely high. The question is whether this could have happened in a climate without global warming.

It was a soaking September for much of Australia’s east, including the Murray Darling Basin.
BoM, Author provided

Researchers led by Pandora Hope analysed the local conditions for rainfall generation in forecasts of the event, under both the current climate and in a model that did not feature human greenhouse emissions. Air moisture levels were very high in both forecasts, but no higher in the current human-influenced climate than it might otherwise have been.

But there is more to rain generation than simply how much moisture there is in the air. Other factors are also important, such as weather patterns that cause moist air to accumulate in certain areas, and local atmospheric instability which is important for storms to form.

The results showed that under current climate conditions, those circulation factors were not as favourable to producing rainfall as they would be in a world without increased levels of carbon dioxide.

In other words, the local environment is generally becoming more stable, so it will be harder for these sorts of extreme rainfall events to develop.


Read more: Is the tropical Indian Ocean to blame for southern Australia’s wet winter?


During July to September 2016 the eastern tropical Indian Ocean was extremely warm, a result of the coincidence of the year-to-year variability of the tropical oceans and a strong ongoing upward warming trend. Rainfall in southeast Australia is often increased when ocean temperatures to the northwest of Australia are unusually high.

Research by Andrew King found that this association is indeed strong, and very important for the heavy rainfall through these months in 2016. But by analysing climate models both with and without the human influence on the climate, he found that human forcing had little influence on the intensity of this extreme rain event, consistent with the findings of the other study described above.

The ConversationThere is clearly still much left to learn about attributing the causes of extreme weather events. But these studies show that examining the effects of climate change on atmospheric circulation can help us better understand humans’ influence on Australian weather extremes.

Pandora Hope, Senior research scientist, Australian Bureau of Meteorology; Andrew King, Climate Extremes Research Fellow, University of Melbourne; Eun-Pa Lim, Senior research scientist, Australian Bureau of Meteorology, and Michael Grose, Climate Projections Scientist, CSIRO

This article was originally published on The Conversation. Read the original article.

Yacaaba Headland Walk


Kevin's Daily Photo, Video, Quote or Link

I ran out of time yesterday to post about my walk up Yacaaba Headland and how I only just avoided being in a storm that was moving in. So today (it’s actually the 27th July 2012 as I type away) I must get two days of posts done, even if I slip this one in back in time, so to speak (as you can with the post time when posting).

BrunchSo I decided to do the Yacaaba Headland walk just before lunch and had lunch in the carpark, while reading the paper. Nothing too healthy – I tend to eat far too much junk when I’m on holidays. So it was a bacon & egg roll, as well as a couple of potato scallops and some chips (and coke of course) See Picture at Left. It was really brunch and I needed the energy boost to accomplish the walk. Sounds…

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