Contributed by Sustainable Communities member, Malcolm McDonell
Three competing challenges for sustainability – biodiversity, water and agriculture. Is there a path through?
Summary: A small area of the state is home to a large proportion of the population. Water is the reason – water is a dominant issue for Adelaide. Our reliance on the River Murray is not secure, so we need to do all possible to maximise water-harvesting in the region. Vegetation plays a key role in this but new approaches are needed. Local agriculture is essential for the city’s fresh produce – part of the demand on water. Caring for these economic considerations should not stop us from caring for local biodiversity.
Adelaide’s situation – biodiversity and food
Colonial agriculture in the Adelaide context has been damaging. Sustainability into the future demands that we balance the management of nature, water and agriculture. Using the tools from a ‘green-kit-bag’ it can be rescued. A suite of reforms is needed.
Historically the region was the homeland of the Kaurna people (in the main). There were fewer than one thousand of them. Presently our population is over one million – one thousand times as much as the 1836 figure.
Our context is Adelaide – the plains and the ranges from the Fleurieu Peninsula to Gawler – the most important, relatively fertile area of SA. It can be thought of as an oasis. This region covers about 10,000 square kilometres of land, and has a population of over one million people – a population density akin to that of Spain, much more intensively used than any of the other major centres in Australia. Adelaide is rated one of the most liveable cities in the world. But our smugness might be premature. Sustainability is the question mark.
In recent years there has been strong community recognition of the issue of biodiversity conservation. Water comes into focus at times of drought and wanes when it rains! Agriculture is little recognised. It is seen as business – part of retail commerce.
Much of Adelaide’s food is imported into the city from the Riverland and east coast. This is part of the cost cutting and mechanized answer to economic efficiency which makes Adelaide a distant suburb of Melbourne, and many business activities in Adelaide have already closed due to this vision. But any city needs a local produce and no long term sustainability is possible without it.
Our fresh produce local comes from the Hills and market gardens of Virginia. The Virginia produce is irrigated from fossil water which is not sustainable in the long term. This water is saline and increasingly so.
Water has always been the challenge for Adelaide. In the early 20th century Adelaide accessed the River Murray to rescue it from shortage of water. But today, in summer it does not flow. Climate change will make it even less reliable and upstream farmers will want to access it. Interstate agreements that guarantee a share for South Australia will easily be broken if conditions are difficult. It is clear we cannot count on the River for our water needs.
South Australia has invested in a de-salination plant for water security, but a carbon hungry plant will not look like a good answer in the long term.
In a similar way the long-haul trucking which supplies food to our supermarkets make large carbon footprint. It is not a good answer. In short we need local agriculture, irrigated by local water. Can we do it? And can we do it in a way that respects biodiversity as well?
The Murray River is not secure as a water source for the future – we need to look at local sources, meaning we have to do more by way of water-harvesting. Only a small percentage (about 5%) of rain is collected at present. The rest flows to the sea, soaks into the ground, or is lost in evapo-transpiration. A decentralized water management can be implemented, where every hill and valley is a source and storage for rainfall. The landscape can be dotted with ponds and dams holding water for irrigation in the adjoining paddocks.
Water-harvesting is a matter of land management. Currently landscapes in the region are usually cleared grassy paddocks, or eucalyptus forests. In the case of cleared land, water runs off it quickly before it can soak deeply into the soil, and open paddocks are baked by direct sunlight. This is not good water management for the health of this environment.
Cleared land allows grass to grow, but in the summer it gives little cover to the ground which gets very hot and any soil moisture is lost. When rain falls it washes over the surface quickly and little penetrates and soaks in. Soil is also lost in this process.
And in the case of eucalypt forest the trees take up most of the water, and little is available in the nearby landscape. This habit of eucalypt forests is not widely recognised in Australia, but is known around the world where eucalypts have been used. For this reason they are being removed from many sites around the world where they have been introduced. Could it be we have a blind spot for the iconic symbol of our land? There is strong sentiment for native forests. However the negative effect they have on water-harvesting suggests we should think again, and weigh up whether our loyalty is misplaced.
A landscape of eucalyptus trees is a desiccated landscape. We have to make the landscape work for our water needs, but not forget the issue of bio-diversity.
The proliferation of eucalypts is not ideal. How then should we manage bio-diversity? Currently 13% of our region is covered in native (conservation) forests. These are not a close resemblance to the forests of 1836 because they are managed without fire – fire which was a commonplace at the time of colonisation. The eucalypts fill out the landscape now where they were fiercely constrained in the pre-colonial era.
We can retain the conservation forests that we have (though new management systems are needed), but especially we should do what can be done for endangered species of plants and animals. Animals and birds are being given some recognition, but our commitment should be at a very high level. In the case of plants there is scope to have more community involvement in their conservation. Many of them are easily cared for in a domesticated environment and this should be taken up by community supporters of conservation.
For the sake of water harvesting we need to adopt a new style of land-management. Eucalyptus forests are not good with water, and cleared land is not good. Just as exotic plants are needed for their utility as food, so also exotics are needed for their utility in water management.
Microclimate for water
How then to harvest water? To make the most of available rainfall, the land should be covered with suitable trees for shade, cooling the understorey level, and making a more humid microclimate. And the soil needs a rich mulch that invites and holds water. Eucalypts do not provide this benefit, but many exotics do. The water can then slowly move through the surface layers of soil. Potentially, the soil is the biggest reservoir of water!
It is widely recognised that a forest with its shade will make a cool ground microclimate. And the soil can be enriched with the leaf litter that is nutrient rich – building the soil carbon content. In this way the depleted soil can slowly be enriched, as it nurtures the moisture it holds.
These hills of vegetation can be in part productive orchards of fruit and nuts and other tree crops, some will be long term plantations with scope for timber production. But essentially they have to nurture the water in the soil. Lower down in the valley bottoms water can be collected in those ponds and dams, and alongside will be market gardens for intensive production of fresh vegetables.
With a system such as this many small irrigated farms could be the source of much of our future food needs.
And in the spirit of decentralization the food can be sold off in local produce markets across the region!