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This report - Ecological Risk Assessment Case Study for the Lower Loddon Catchment: Bayesian decision network model for predicting grey-crowned babbler population abundance in the Lower Loddon catchment - is the fourth in a series of five produced by NPSI project UMO45 Delivering Sustainability through Risk Management.

The ecological risk assessment conducted in this study was focused on the assessment of the ecological health of the Lower Loddon River and its catchment. The aim of the risk assessment was to provide local resource managers with a better understanding of risks to the Lower Loddon River and catchment, and the effectiveness of different management actions in protecting and rehabilitating the river. A Bayesian decision network (BDN) model for predicting river farmland ecological values in the Lower Loddon River was developed and full details are provided in this report. Farmland Ecological Values are defined as the value of farmland to the ecological assets of the larger catchment within which farms exist, but not values directly associated with agricultural production (i.e. the crops themselves are generally regarded as a separate ‘value’).

Specifically, the ecological values included the role of farmland and surrounding areas to wider biodiversity and to specific species of indigenous fauna and flora. This is essentially restricted to ecological uses of farmland for foraging or for habitat in the parts of farmland not affected by seasonal disturbances such as harvesting, such as shelter-belts or riparian zones preserved for stream water quality. Areas of farmland under direct cultivation are generally unsuitable for habitat. The abundance of a common bird species - the grey-crowned babbler – was used as the measure of farmland ecological value, and a BDN model developed to predict population abundance of the grey-crowned babbler.

The structure of the BDN model was based on a conceptual map constructed by stakeholders in an initial workshop, and included four main factors that influenced population abundance of the grey-crowned babbler – habitat availability, food availability, biological factors and socio-economic factors. In the preliminary model reported here, socio-economic factors and some other variables (e.g. catchment landuse, groundwater quality, hydrology) were not included because of a lack of data and information, but could be included in the next iteration of the model. The BDN model predicts that for existing conditions, there is a high probability of low population abundance of the grey-crowned babbler.

Sensitivity analysis showed that poor habitat and low ‘biological potential’ (i.e. the effect of a combination of biological factors such as competition, reproduction and predation) had the greatest influence on the abundance of the grey-crowned babbler populations. The model was also used to predict the effect of stock access on remnant forest area and on the abundance of grey-crowned babbler populations. Reducing stock access was predicted to significantly improve the probability of medium to high abundance of grey-crowned babbler populations from around 40% when stock access was high to around 81% for low access. These results support the current Loddon catchment management plan, where major onground fencing works are being implemented to reduce stock access to the riparian zone and will be extended to include fencing of remnant catchment vegetation.