Using local knowledge to identify drivers of historic native vegetation change

Research underway with three Catchment Management Authorities in Victoria (Goulburn Broken, North Central and North East) is examining the impacts these bodies have had, and could potentially have, on native vegetation extent and quality (condition) on private land. This paper outlines how local knowledge together with spatial data and ecological information is being used to develop Bayesian Networks (BNs) that show historic changes in native vegetation quality and extent in three regions of northern Victoria since the 1880's. The research is being focused on three case study areas, one located in each partner CMA (Figure 1). Comparison of aerial photography from 1946/7 with contemporary modelled tree canopy cover identified that native vegetation extent has increased or decreased to varying degrees over time and space in each case study areas. Local knowledge elicited from the regional workshops has identified the catalysts of change over time as including episodic events, the viability of the farming industry, demand for 'lifestyle' properties, rabbit control, NRM and Landcare initiatives and policy instruments. Changes in extent and quality of native vegetation varied spatially and temporally across the landscape depending on the presence of remnant native vegetation, land tenure, agronomic potential of the land, historic events (e.g. bushfires), characteristics of the local population and targeted policy instruments. Expansion and intensification of farming between the mid-1950s and the late 1970s was matched by a general decline in the extent of woody native vegetation on private land. A decline in farm profitability from the 1980s to 2006 was associated with declines in farm employment, the number of farmers, population, and businesses and services in small rural towns dependent on agriculture and increases in 'lifestyle' farming around rural towns and regional centres. A general increase in the extent of woody native vegetation on private land was noted over this period by workshop participants. BNs are being used to integrate local knowledge on historic land cover and vegetation change, and its drivers, with analysis of spatial data to capture changes in condition over time (60+ years). The regional workshops have been crucial in developing conceptual understanding of the relationships between external drivers (e.g. climate, market forces), actions (e.g. land clearing, de-stocking, revegetation) and outcomes (e.g. vegetation change). The knowledge and understanding of changes in land use and management and their drivers that was gained from the workshops have been used to refine the influence diagram for the historic vegetation extent and quality BNs, define the details of each variable (e.g. states, key assumptions) and identify key decades to represent in the models.