Importance of our land
Introduction
For purposes of this section, ‘land’ refers to the variety of terrestrial plants, animals and micro-organisms, and the ecosystems of which they form part. Over millennia, the Earth’s (and SA’s) plants, animals and microbes became increasingly more diverse due to evolution, climate, competition and symbiosis. With this came enhanced interaction and interdependence within increasingly complex ecosystems.
Interactions between and within species in an ecosystem can be simple or complex, competitive or beneficial, or predatory or symbiotic. Examples of these interactions include:
- coevolution of plants and herbivores leading to greater diversity and dispersion of seeds
- exchange of nitrogen and carbon between microbes in soil and plants.
Collectively, this diversity of animals (birds, mammals, reptiles, fish, amphibians and invertebrates), vegetation, soil, biogeochemical cycles and microorganisms provides a range of essential ecosystem services such as:
- purification of air and water
- pollination, seed dispersal and pest control
- soil generation and fertilisation
- detoxification and decomposition of wastes
- flood and drought mitigation
- ultraviolet protection
- climate stabilisation.
Besides the economic value of ecosystems, such as the reliance of the pastoral industry on native vegetation, species and ecosystems also have intrinsic, spiritual, cultural, inspirational and educational values. Places like the Coorong in south-east SA, for example, have important cultural and spiritual value, while the gibber plains (or ‘stony country’) is critical for pastoral enterprises and habitat for unique and threatened species. The stony country also provides an abundance of sharp stone fragments, which were much used by Indigenous people for making tools.
According to SA’s No Species Loss Nature Conservation Strategy 2007–17:
Biodiversity sustains our natural and production landscapes and the industries using them. As South Australians we share in and enjoy the societal and economic benefits of the biological wealth of biodiversity. Our quality of life, our sense of place and our cultural identity are intimately linked to the biodiversity surrounding us.
Much of SA’s economy is based on the use of biological resources – tourism and recreation, nature conservation, pastoralism, agriculture, horticulture, forestry, aquaculture and fishing all benefit from healthy ecosystems. Our primary production systems require biodiversity for pest control, soil production and stabilisation, pollination, salinity amelioration and water purification. Our survival depends on natural environments functioning well. The survival of our plants and animals depends on healthy ecosystems.
Soil
Soil is literally the foundation of the health of our ecosystems, and is a product of chemical, physical and biological characteristics. Soils contain more biodiversity than exists above ground. Soil organisms range from single-celled microorganisms to nematodes living in the water film on the surface of soil aggregates, and microarthropods living in air-filled soil pores to larger soil animals, such as earthworms and other ecosystem engineers that can manipulate soil structure creating their own habitat.
Fauna found in soil core samples
The higher the abundance of beneficial microbes, the healthier the soil in terms of better plant growth and lower disease incidence, and higher nutrient content, soil enzyme activities and soil pH.
The number and types of organisms in soils vary from one system and environment to another based on soil type, land management practices, leaf deposition, animal waste and decomposition, and local climatic conditions.
Soil organisms:
- act as driving agents for nutrient cycling
- regulate the dynamics of soil organic matter, soil carbon sequestration and greenhouse gas emission
- modify soil physical structure and water regime
- enhance the amount and efficiency of nutrient acquisition by vegetation
- enhance plant health.
This excerpt describes how soil, a complex ecosystem, is biologically, physically and chemically diverse. It also highlights soils as being formed over a long period of time through interactions between weathering of parent material, local climate and topography, and the thousands of organisms (soil biota).
The thin layer of soil that forms a patchy covering over the continents controls our own existence and that of every other animal of the land. Without soil, land plants as we know them, could not grow and without plants no animals could survive.
Yet, if our agriculture-based life depends on the soil, it is equally true soil depends on life, its very origins and the maintenance of its true nature being intimately related to living plants and animals. For soil is in part a creation of life, born of a marvellous interaction of life and non-life eons ago. The parent materials were gathered together as volcanoes poured them into fiery streams, as waters running over the bare rocks of the continents wore away even the hardest granite, and as the chisels of frost and ice split and shattered the rocks. Then living things began to work their creative magic and little by little these inert materials became soil.
Life not only formed the soils, but other living things of incredible abundance and diversity now exist within it; if this were not so the soil would be a dead and sterile thing. By their presence and by their activities the myriad of organisms of the soil make it capable of supporting the earth’s green mantle.
Rachel Carson, Silent Spring, 1962
It takes about 500 years to form 25 mm of soil under agricultural conditions and about 1,000 years to form the same amount in forest habitats. Soil should be treated as a non-renewable resource.
Soils provide a range of essential ecosystem services. In particular, soil and its biota are essential for agricultural production, providing a high proportion of our food. Soils are also important for regulating water retention and infiltration rates. This replenishes groundwater and provides clean drinking water while mitigating the effect of floods and droughts.
At the same time, increased infiltration/retention rates decrease surface water runoff, which helps minimise nutrient loss and soil erosion vital for sustainable agricultural production. Greater infiltration and retention rates also help prevent siltation and nutrient enrichment of rivers and lakes.
Soil biota are essential for biogeochemical cycling, which supports plant production and affects global climate regulation, primarily by influencing global carbon dynamics. Soils, and the biomass they contain, function as a carbon storage system with about 2,500 petagrams (1 Pg = 1018 g) of carbon stored in soils globally. Other essential services provided by soil biota are decomposition of organic matter and suppression of soil-borne diseases and pests.
The Soils of Southern South Australia, published in 2009, describes the broad range of soils in SA, in particular in the temperate region. South Australia’s long and varied geological and climatic history has produced a diverse range of soils, which underpin the productive use of the land and the health of our natural environments.
Differences in soil properties are reflected in differences in soil composition, structure, salinity, depth, water holding capacity and erosion propensity. A total of 61 soil types have been mapped across SA’s agricultural lands.
Plants
Animals
Similar to plants, animals are an essential part of our state’s biodiversity and, in addition to their intrinsic value, provide for a number of human needs, such as food, pollination, tourism, spiritual beliefs, cultural practices, scientific knowledge and a sense of place and identity.
Vertebrates
Australia has more endemic mammals and reptiles than any other country in the world. Of Australian mammals, 87% are found nowhere else in the world. In the case of reptiles and amphibians, 93% and 94% respectively are unique to Australia. As a reflection of their greater intercontinental mobility, the proportions of birds and fish endemic to Australia are 45% and 24% respectively.
Our native species play an important role as co-managers of our land. Examples are as follows:
- Bats and birds help control pest insects and spread seeds.
- Native predators help to control invasive species, such as rabbits, foxes and cats.
- Small mammals, including bettongs and bilbies, help maintain healthy soils.
The Census of South Australian Vertebrates describes the taxonomy and physical distribution of the broad range of mammals, birds, reptiles, amphibians and freshwater fishes in SA. It also includes the extinction threat status of species where applicable, that is, already extinct or endangered and vulnerable to extinction.
Invertebrates
Australia’s terrestrial invertebrates are less well known, with only a small proportion having been formally described.
Of the estimated 300,000 species of terrestrial invertebrates, many are endemic to Australia – more than 80% of all the cicadas, leafhoppers, true bugs and ants. This is because of our long geological isolation from other continents, wide range of habitats, including tropical, temperate, semi-arid and arid regions, and a landscape dominated by many different species of endemic flora.
Invertebrates have exploited the many food sources and niches these plants offer. As a result, it is estimated that a third of all foliage-feeding insects in Australia depend on our native eucalypts and acacias.
In response to crop damage caused by some insects, our typical defence has been to apply synthetic pesticides. This has caused serious harm to other insects such as bees, which produce essential ecosystem services. Increasingly, more use is being made of less harmful biological methods that rely on the natural enemies of pests to control them.
Dinosaur Ant
Praying Mantis. Source: CSIRO
Tiger Beetle. Source: South Australia Museum