7.3 The qualitative system dynamics model of the WA agricultural region
7.3.2 Ecosystem Loop
These together will affect the capacity of the commodity system. A state variable represents a stock or level in a system and is a point of accumulation.
It is often the rate of change in a stock that is responsible for producing oscil- lations in system behaviour and the development of persistent, undesirable and unintended effects (Sterman, 2000). This may appear as overshoot and collapse in state variables.
In order to read this model we will start with the Efficiency Boosting Loop and the individual producer’s need to increase efficiency and scale. The production growth drivers push down prices and the farmer terms of trade, reducing farmers’ financial capacity and increasing the need for increasing efficiency and scale. The response is to increase the size of the land holding through land purchase or clearing of land, as shown in the model by the variable ‘Efficiency and scale’. The production benefits that can be gained from clearing native vegetation are rarely uniform. The best quality agricul- tural land, with high production benefits per hectare, was cleared first. As this high quality land becomes scarcer, attention turns to lower quality land where some commercial benefits are still available from clearing (Aitken and Rolfe, 2000). Recent precision farming techniques are now showing that farming these marginal soils has little commercial benefit (Passioura, 2002) and in the process of increasing efficiency it is expected that some of these marginal soils will be retired out of production. However, in some areas increased application of micronutrients will maintain production.
The consequences of the wheat commodity system in the WA agricultural region are the cumulative negative impacts on natural resources, discussed in Chapter 3. Although soil salinity is considered to be one of the most serious off-site consequences of agricultural production (Chapter 3), other depleting mechanisms, such as soil erosion, also occur. The Resource Depletion Loop (B1) identifies some of the important causes and effects of these processes.
The Resource Depletion Loop can be described as follows: the need for expansion drives the clearing of native vegetation, which will increase the area affected by soil salinity caused by changes in the hydrological cycle. This is a slowly changing biophysical process, the effects of which may be distant in both time and space. Increased soil salinity has four causal pathways.
Firstly, it reduces the area of native vegetation; secondly, it reduces the area of productive agricultural land; thirdly, it reduces biodiversity; and fourthly, it impacts on water quality. Loss of biodiversity and poor water quality will reduce ecosystem services and thus the ecological capacity. Resource deple- tion includes the impact on soil properties, for instance increasing soil erosion, soil acidity and sodicity, which are the effects of agricultural production and which reduce ecosystem services. The protection of native vegetation
is important, not only because of its biological diversity and uniqueness, but also because of the part it plays in maintenance of ecosystem processes.
The Environmental Pollution Loop (Figure 7.9, B4) tracks the effects of the commodity system (through the variable ‘Efficiency and scale’) on soil and water properties and ecosystem services, which together reduce the ecological capacity. The Environmental Pollution Loop can be described thus: increases in the variable ‘Efficiency and scale’ may cause impacts through greater intensification of farming. Land management practices may be intensified and cause changes in soil properties, for example, through increased fertiliser, pesticide and herbicide application which have both on- and off-site effects.
Runoff can affect water quality through the process of eutrophication of waterways, an externality in economic terms reducing ecosystem services.
The multiple feedback loops will combine to impact on ecosystem services and ecological capacity. Depending on the strength of the reinvestment reinforcing loop in the commodity system, the reduction in ecological capacity may cause an impact on the productive capacity of the commodity system.
The Resource Depletion and Environmental Pollution Loops are balancing loops which may act to limit total commodity production and bring about equilibrium and stasis, and may in time become a strong signal within the system through either information flow or material flow. However, at the present time the feedback signal is weak in material flow and largely ignored as information flow or both. There are potentially two reasons for the weakness in strength of the signal. Firstly, its weakness is related in part to the long time delay in the development of symptoms in the ecosystem, and in symptoms becoming visible and at a great enough level to be considered a significant problem. The delay is in the order of a few years to 300 years for significant areas of soil salinity to develop following the clearing of native vegetation (Hodgson et al., 2004). Secondly, often the cause and effect are not only distant in time but also distant in space, the symptoms appearing in different parts of the ecosystem.
Desired states (goals) of the systems are an integral part of all balancing feedback loops and in terms of resilience theory. For example, in Figure 7.9 as resources are depleted and environmental pollution occurs, ecosystem services and ecological capacity are reduced and may cause the system to eventually reach a new state or endogenous goal of the system. The discrepancy in the ecological capacity is the difference between the socially desired state of ecological capacity and its actual state. The desired ecological capacity is culturally and temporally defined. For example, the increasing shortfall in the ecological capacity in Australia was responsible for the Landcare movement described in Chapter 2.