A qualitative model was developed to describe the ecological community associated with the ‘Rainforest’ Figure 33). The model focused on the functional aspects of tree, shrub (tall and short) and vine vegetation, their ecological roles, and their dependency on soil moisture and (Figure 33). Tall shrubs are an important source of shade, which under optimal conditions, benefits shorter shrubs and contributes to a humid microclimate close to the ground (Figure 33). Shrubs also produce fruits that sustain populations of fruit-eating birds, mammals and arboreal invertebrates. Shrubs and vines provide habitat structure important for arboreal invertebrates and their leaf litter maintains surface soil moisture and is a food resource for soil-dwelling invertebrates (Figure 33). Both groups of invertebrates are a key food resource for frogs, birds, mammals and reptiles. These insectivores are in turn preyed upon by snakes, other reptiles, birds and mammals, which in turn are also being consumed by predatory birds and goannas (Figure 33).(
A significant threat described in this system are populations of feral pigs, which consume the fruits of shrubs and plough through the upper soil layers in search of roots as well as frogs, reptiles and insects (Figure 33).). They are a major source of disturbance to the system that destroys the humid microclimate of the forest floor. Fragmentation from land clearing similarly compromises the humid microclimate, and decreases the amount of shade and habitat structure ( ) (
Trees and tall shrubs access and use deep soil moisture while shrubs and vines use shallow soil moisture (Figure 33). Where available, perched groundwater tables are accessed by all types of forest vegetation in the model. There was speculation regarding the role of trees in lifting water from depth and releasing it into surface soil ( ); but specific attributes of this process were considered to be relatively uncertain (Figure 33). The principal impact of coal mining was described as a possible lowering of the groundwater table from open-cut mining, which could then limit replenishment of deep soil moisture or even make it too deep to be accessed by tree roots. This effect, however, was deemed as being uncommon or slight for this over most of the area of interest in the . Rainforests in this part of the Namoi subregion may access perched groundwater but were considered unlikely to be dependent on deeper groundwater ( ). However, fauna from adjacent lowlands may use rainforests as a seasonal refuge and this may increase if the lowland is drawn down (Figure 33).
Model variables are: canopy insects (CI), deep soil moisture (DSM), fruit-eating birds and mammals (FEB&M), fragmentation (Frag), frogs (Frogs), fruits (Fru), goannas (Goan), groundwater table (GWT), humid microclimate (HMC), habitat structure (HS), insectivorous reptiles (IR), litter (Lit), pigs (Pigs), predatory birds (PB), perched groundwater (PGW), soil-dwelling insects (SDI), shade (Sha), small insectivorous birds and mammals (SIB&M), snakes (Sna), shorter shrubs (SS), surface soil moisture (SSM), tall shrubs (TS), trees (Trees), vines (Vines).
Data: Bioregional Assessment Programme ()
Surface water and groundwater modelling predict significant potential impacts to the watertable, from which a single cumulative impact scenario (C1) was developed (Table 44).
Table 44 Summary of the (cumulative) impact scenario (CIS) for the rainforest ecosystem
Pressure scenario is determined by a decrease (–) in the following signed digraph variables: groundwater table (GWT).
Qualitative analysis of the signed digraph model (Figure 33) generally indicates a negative response prediction for most biological variables within the rainforest as a result of decreasing the groundwater level (Table 45). A predicted decrease in pigs leads to reduced predation of insectivorous reptiles, a predicted increase of which also favours goannas.
Table 45 Predicted response of the signed digraph variables in the rainforest ecosystem to (cumulative) changes in hydrological response variables
Zero denotes completely determined prediction of no change.
Data: Bioregional Assessment Programme ()
Product Finalisation date
- 2.7.1 Methods
- 2.7.2 Prioritising landscape classes for receptor impact modelling
- 2.7.3 'Floodplain or lowland riverine' landscape group
- 2.7.4 'Non-floodplain or upland riverine' landscape group
- 2.7.5 Pilliga riverine landscape classes
- 2.7.6 'Rainforest' landscape group
- 2.7.7 'Springs' landscape group
- 2.7.8 Limitations and gaps
- Contributors to the Technical Programme
- About this technical product