Landscape and soil

2016

Under natural conditions, the land (i.e. landforms, soils, drainage networks of streams and rivers, vegetation and other biota) is in some sort of equilibrium with the climate and disturbance factors such as bushfire. This equilibrium is disturbed by land management, because changed practices can occur faster than the land’s ability to respond and achieve a new equilibrium. As a result, the land is in a constant state of change. Whereas some changes may be acute, such as landslides, most changes are chronic, such as slow acidification of soil, gradual habitat change and low levels of sediment loss. These chronic changes may pass unnoticed, can be difficult to monitor, and often pose the greatest challenge to land managers.

Resilient land should provide a long-term, optimal mix of ecosystem services, relative to its environmental context. In general, good-quality and resilient land has these related features:

  • Nutrient levels are maintained, with neither significant nutrient depletion nor nutrification taking place.
  • Biological production is high relative to the potential limits set by climate.
  • Levels of biodiversity are relatively high.
  • Rates of soil erosion and deposition are low, with only small quantities of soil transferred out of the system (e.g. to the marine environment).
  • Contaminants are not introduced into the landscape, and existing contaminants are not concentrated to levels that cause harm.
  • Systems for producing food and fibre for human use do not rely on large net inputs of energy, either directly through physical management or indirectly through the addition of agrichemicals.

At the heart of the resilience question is how we manage the land and its assets. Significant land management issues that will have major consequences for current and future land resilience include the following:

  • How do we increase agricultural productivity without destroying the provision of ecosystem services that we also rely on?
  • How do we resolve the competition for access to land between agriculture and the resources sectors; urban development and infrastructure provision; and environmental stewardship, cultural and recreational needs?
  • In a changing world, how do we maintain or increase natural resilience to enable the land to equilibrate to new climates while preserving the biodiversity, productivity and ecosystem services that we desire?

Agricultural productivity can be increased by increasing the productivity of existing agricultural practices, or by expanding the area under agriculture. Increasing productivity typically means intensification, which usually means increased inputs of nutrients, pesticides, time and other resources. Increased productivity can also be achieved through increased efficiencies, such as better targeted inputs, both in time and space, to improve their impact, and better conversion of resources into desirable products, such as milk, grain, meat and fruit. Improved targeting should also mean reduced loss of nutrients and wastage of pesticides. In a continent with naturally poor soils, nutrification can significantly change recruitment dynamics, favouring exotic grasses over native species (Duncan et al. 2008). Nutrient run-off is still a significant threat to the Great Barrier Reef (Queensland Government 2013) and inland waterways (see the Inland water report). However, whereas the risks posed by insufficient nutrient addition are borne by the farmer concerned, the risks posed by overapplication and run-off of nutrients are often felt downstream of application. For example, there is a trend towards increasing application of nitrogen in cotton in irrigated systems, which increases the potential for movement of fertiliser offsite (Braunack 2013). There are also anecdotal suggestions that some cane farmers are routinely applying fertilisers at above recommended rates, ‘just in case’. This suggests that the way in which we perceive and discuss risk needs to be refined.

Competition for land does not of itself affect landscape resilience, but the consequences of different land management options can. While some land uses—for example open-cut mining and intensive agriculture—are mutually exclusive at the same point in the landscape, resilience can be increased through creative thinking about associated landscape features. Thus, it is possible to protect and conserve the resilience of natural systems in parallel with different land uses—for example, through sensitive management of natural environments within mining tenements and urban areas.

Maintaining the natural resilience of the landscape, and increasing resilience against future climate change, sea level rise and extreme events require improved understanding of what determines resilience today. There is a good understanding of the physical and chemical nature of our soils, and their distribution, but there is a very poor understanding of soil biology and the function of soil microbial communities, in particular. It is known neither to what extent the resilience of natural and even agricultural soils is mediated by microbes, nor whether the current degradation of this community is ongoing or especially threatened by climate change. The BASE project—Biomes of Australian Soil Environments (Bissett et al. 2016)—is a collaborative, proof-of-concept project to generate a national framework dataset of Australian soil microbial communities. This will go some way to highlighting the paucity of our knowledge, but considerably more work will be required to understand how the microbiota interact with each other, with plants and with the environment.

cyclone_yasi_rs.jpg

Effect of severe tropical cyclone Yasi on coastal vegetation: erosion, redeposition of sand, and denudation or uprooting of vegetation,
Meunga Creek, near Cardwell, Queensland 

Photo by Dan Metcalfe, CSIRO

Metcalfe D, Bui E (2016). Land: Landscape and soil. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/theme/land/topic/2016/landscape-and-soil, DOI 10.4226/94/58b6585f94911