Welcome to the first edition of Beating Around the Bush, a series that profiles native plants: part gardening column, part dispatches from country, entirely Australian. Read more about the series here or get in touch to pitch a plant at email@example.com.
The Bunya pine is a unique and majestic Australian tree – my favourite tree, in fact. Sometimes simply called Bunya or the Bunya Bunya, I love its pleasingly symmetrical dome shape.
But what I really love about it is that there are just so many bizarre and colourful stories about this tree – the more you learn, the more you find it fascinating. (That is, unless the tree has harmed you; they come with some hazard warnings.)
Curious Kids: Where did trees come from?
Can you grow it?
Bunya pines (botanical name: Aracauria bidwilli) are living fossils. They come come from a fascinating family of flora, the Araucariaceae, which grew across the world in the Jurassic period. Many of its “cousins” are extinct. The remaining members of the family are spread across the former landmasses of Gondwana, particularly South America, New Zealand, Malaysia and New Caledonia, as well as Australia.
This family includes one of the most amazing botanical discoveries of the 20th century, the Wollemi pine (Wollemia nobilis).
Bunyas used to be much more widespread than they are now. Today they grow in the wild in only a few locations in southeast and north Queensland. One such area, the Bunya Mountains, is the remains of an old shield volcano – about 30 million years old, with peaks rising to more than 1,100 metres. The Bunya pines grow in fertile basalt soils in this cool and moist mountain environment.
If you want to grow a Bunya, I would suggest that you need a large garden. The tree needs fertile and well-drained soil, and regular watering in drier climates. A shaded position will also help – it can struggle in direct sunlight in its youth.
Bunyas also produce highly valued timber, which is used for musical instruments. It is particularly valued as “tonewood” for producing stringed instruments’ sound boards. Saw logs for Bunyas come from plantations only, as they are protected in their national park wild habitat.
Stand well back!
While many people love Bunya pines, this love affair comes with a health warning. They are best regarded with both distance and respect!
The trees are big and typically range from 20m to 50m in height. Their leaves have strings of very rigid and sharply pointed leaves. If you come into physical contact with its leaves or branches, you must wear protective clothes and carefully handle them to avoid pain or even cuts. As a child, the swinging branch of a Bunya made a formidable garden weapon.
But that is nothing compared to this tree’s ability to hit you on the head, possibly with serious consequences. When in season (generally December to March) they can produce dozens of massive cones weighing up to 10 kilograms. These can drop from up to 50m without warning.
I first learned of this when a fellow university student in the 1980s scored an impressively large Bunya cone dent in the roof of his battleship-solid FB Holden ute. My university campus has beautiful gardens displaying dozens of massive Bunyas, but one was perhaps a bit close to the car park. My university friend was lucky not to get hit. Many people have not been so lucky and some have even been hospitalised.
Bunya pines are beautiful trees in large gardens and are a feature of parks around Australia, but their habit of “bombing” people and property causes considerable angst. Many local councils erect warning signs or rope off the danger zone during cone season. Others hire contractors to remove the cones to protect their residents (and perhaps limit their own legal liability). Sadly, some Bunya pines have been cut down to remove the risk.
The cultural connection of the Bunya pine to Aboriginal Australians is very powerful. The Bunya Mountains in southeast Queensland used to host massive gatherings of Aboriginal groups.
People came to visit the Bunya pines and feasted on the nuts in their abundant cones. Some travelled from hundreds of kilometres away, and traditional hostilities were dropped to allow access. The seed in the Bunya cone is a delicious and nutritious food, a famous and celebrated example of Australian bush tucker.
Today some trees remain marked with hand and foot holes that Aborigines made in the trunks of older Bunyas. The climbers must have been brave and agile to harvest the cones from such heights.
Sadly, the last of the Aboriginal Bunya festivals was held in about 1900, as European loggers came to the area for its many timber resources.
But even those European timber pioneers realised the significance of the Bunya Mountains area. The Bunya Mountains National Park was declared in 1908, creating Queensland’s second national park.
New South Wales’ proposed brumby legislation – which abandons plans to cull feral horses in Kosciuszko National Park – is a dangerously reckless policy that will escalate environmental impacts, escalate costs, and put horses at risk of extreme suffering.
But the evidence regarding feral horse (brumby) impacts on the environment in the Australian alps makes it clear that large numbers of feral horses are incompatible with maintaining the ecological values of Kosciuszko National Park.
Reports to both the Victorian and NSW governments have expressed concern over the impact on threatened species unless horses are culled. In NSW, horses directly destroy the habitat of already threatened species, including two species of critically endangered corroboree frogs, the critically endangered smoky mouse, endangered reptiles like the alpine she-oak skink and Guthega skink, and several plant species.
In its report, Parks Victoria suggested that native mammals such as wallabies and kangaroos are also out-competed and driven away by feral horses.
The threat posed by feral horses to native species and communities is so great that the NSW Threatened Species Scientific Committee has released a preliminary determination to list feral horses as a key threatening process. This report demonstrates that feral horses have well established environmental impacts and that action to reduce this threat is now urgent.
What’s more, there may be no “safe level” of feral horse numbers, below which the environment can cope with the damage. In a new report for the Victorian government, the impacts of feral horses on the Bogong High Plains was found to be cumulative, meaning that the damage caused by even a small number of horses accumulates over time, because the rate of recovery in alpine conditions is extremely slow.
Contrary to the “brumby bill” which would leave thousands of feral horses in Kosciuszko National Park, and contrary to the draft management plan that would reduce feral horses down to 600 over 20 years, to prevent horse damage, all of the horses must be removed.
Removing all of the feral horses from Kosciuszko National Park is also a value judgement. NSW sets aside only 9.2% of its land in protected areas. That’s less than 10% where nature conservation has priority, and more than 90% where people and our livestock and crops take precedence. This is already an extreme compromise, and does not even reach international targets under the Convention on Biological Diversity to have 17% of land area in protected areas.
The brumby bill will worsen this already below-par compromise by reneging on commitments to protect Australian native species, and transforming our national park into a playground for escaped exotic livestock.
The bill proposes to move horses from sensitive areas into less sensitive parts of the national park. But this is likely to fail, for two reasons. First, there is no clear way that this could be achieved without great cost and horse suffering.
Trapping horses has been experimented with since 2008, with, on average, 450 horses removed from Kosciuszko each year, at a cost of more than A$1,000 per horse. This was from open woodland habitat with good road access. But many of the most sensitive environments are in the least accessible areas, such as the main Kosciuszko range.
Without culling, it is not clear how parks staff could remove horses from these areas. At best, it would be expensive because it would be so labour-intensive. It would require new infrastructure in remote areas (which is undesirable for several reasons), and could require mustering with helicopters, also very costly. Mustering, trapping and trucking horses have serious animal welfare concerns, making them a crueller alternative than culling.
Second, moving more horses into areas that are already overrun by these quadrupeds places the horse population at risk of ecological collapse. Horse populations can increase at 20% or more every year. There were 6,000 horses in Kosciuszko National Park in 2014, so there could be more than twice that number by now.
By moving horses from one part of the park to another, the brumby bill will inevitably lead to unprecedented horse densities relative to the food available. There would be a real risk of mass horse starvation. By ignoring these basic ecological processes, the bill is likely to preside over more horse suffering than would be caused by a cull.
The proposed legislation is bad for horses, disastrous for the environment and, if relocations are actually implemented, extremely expensive. There are less cruel, cheaper, and more environmentally friendly solutions to this problem. Cull the horses in the national park (the least cruel of the range of viable methods), constrain brumby herds to the many private properties around the park to foster innovation in ecotourism, and invest in other environmentally friendly cultural activities to celebrate brumby culture, such as horse events outside the park, signs such as those around Victoria’s alpine huts, sculptures, poetry and movies.
This is the win-win solution we should be aiming for, not the reckless version on the table at the moment.
This article was amended on May 22, 2018, to clarify that the brumby population in Kosciuszko National Park was 6,000 in 2014, not 2016 as previously stated.
Microplastics in the ocean, pieces of plastic less than 5mm in size, have shot to infamy in the last few years. Governments and businesses targeted microbeads in cosmetics, some were banned, and the world felt a little better.
Dealing with microbeads in cosmetics is a positive first step, but the reality is that they are just a drop in the ocean (less than a billionth of the world’s ocean).
Microplastics in soil may be a far greater problem. Norwegian research estimates that in Europe and North America, between 110,000 and 730,000 tonnes of microplastic are transferred to agricultural soils each year.
Here lies the issue: we know almost nothing about microplastics in global soils, and even less in Australian soils. In this article we take a look at what we do know, and some questions we need to answer.
How microplastics get into agricultural soil
Sewage sludge and plastic mulch are the two biggest known contributors of microplastics to agricultural soil. Australia produces about 320,000 dry tonnes of biosolids each year, 55% of which is applied to agricultural land. Biosolids, while controversial, are an excellent source of nutrients for farmland. Of the essential plant nutrients, we can only manufacture nitrogen. The rest we must either mine or recycle.
Sewage treatment plants receive water from households, industry, and stormwater, each adding to the load of plastics. Technical clothing such as sportswear and quick-dry fabrics often contain polyesters and polyamides that break off when clothes are washed. Tyre debris and plastic films wash in with the stormwater. Treatment plants filter microplastics out of the water, retaining them in the sludge that is then trucked away and spread over agricultural land.
In agriculture, plastic mulch suppresses weeds, keeps the soil warm and damp to assist germination, and improves yield. Over time, these mulches break down, and some fragment into smaller pieces.
Biodegradable bioplastic mulches are designed to break down into carbon dioxide, water, and various “natural substances”. Environmentally friendly plastics are often more expensive, raising the question of whether businesses will be able to afford them.
Other potential sources of plastics in agricultural soil include polymer sealants on fertilisers and pesticides, and industrial compost. Unsold food is often sent to the composting facility still in plastic packaging, and with plastic stickers on every apple and kiwi fruit.
The Australian Standard for composts tacitly recognises that microplastics are likely to be present in these products by having acceptable levels of “visible contamination”. Anyone who has bought compost or garden loam from a landscaping supplier may have noticed pieces of plastic in the mix.
In horticulture, particularly as green walls and green roofs grace more buildings, polystyrenes are used deliberately to make lightweight ‘soil’.
There might be other pathways we don’t know about yet.
What happens once microplastics are in the soil?
Here we stand at the edge of the cavernous knowledge gap, because we don’t know the effect of microplastics in our soil. The overarching question, physically and biologically, is where do microplastics go?
How plastics fragment and degrade in the soil depends on the type of plastic and soil conditions. Compostable, PET, and various degradable plastics will behave differently, having different effects on soil physics and biology.
Fragments could move through soil cracks and pores. Larger soil fauna might disperse fragments vertically and laterally, while agricultural practices such as tillage could push plastics deeper into the soil. Some fragmented plastics can absorb agrochemicals.
Soil microbes can break down some plastics, but what are the byproducts and what are their effects? Newer, biodegradable bioplastics theoretically have limited impact as they break down into inert substances. But how long do they take to break down in different soil and climatic conditions, and what proportion in the soil are non-degradable PET plastics?
Both the main form of carbon in soil and polythene (the most common type of plastic) are carbon-based polymers. Could the two integrate? If they did, would this prevent plastics from moving deeper into the soil, but would it also stop them breaking down?
Could plastics be a hidden source of soil carbon storage?
Bioaccumulation is when something builds up in a food chain.
Research into microplastic accumulation on land is sparse at best. A 2017 study in Mexico found microplastics in chicken gizzards. In the study area, waste management is poor and most plastics were ingested directly from the soil surface as opposed to having bioaccumulated.
Nematodes can take up polystyrene beads suggesting some potential for bioaccumulation, however earthworms have reduced growth rate and increased mortality when they ingest microbeads.
Larger microplastics are unlikely to cross plant cell membranes, but it’s possible that plants can absorb the chemicals formed when plastic degrades. Plants have natural mechanisms to keep contaminants out of their fruiting bodies – pieces of plastic in apples or berries is highly unlikely – but root vegetables and leafy greens are a different story.
Metals can accumulate in leafy greens and the skin of root vegetables – could plastics or their byproducts do the same?
This is before we even get to nanoplastics, which are 1-100 nanometres wide. Can plant roots can absorb nanoplastics, and can they pass through an animal’s gut membrane?
Where to now?
The first step is to quantify how much plastic is currently in the soil, where it is, and how much more to expect. This is more difficult in land than water, as it’s easier to filter plastics out the ocean than to separate them from soil samples. The smaller the plastics are, the harder they’ll be to track and identify – which is why research must start now.
Research needs to address the different types of plastics, including beads and other synthetic fibres. Each is likely to act differently in the soil and terrestrial ecosystems.
Understanding how these plastics react will inform the next obvious questions: at what quantity do they become hazardous to soil, plant and animal life, and how can we mitigate this impact?
Plastics in soil represent artefacts of human civilisation. Soils are full of human artefacts; if this was not the case then there would be no field archaeology. However, the effects of microplastic may persist far longer than our own civilisation. We must fill in our knowledge gaps swiftly.
Alisa Bryce, Research Affiliate, University of Sydney; Alex McBratney, Professor of Digital Agriculture & Soil Science; Director, Sydney Institute of Agriculture, University of Sydney; Budiman Minasny, Professor in Soil-Landscape Modelling, University of Sydney; Damien Field, Associate professor, and Stephen Cattle, Associate professor, University of Sydney