USING AERIAL MAPPING TO ANALYSE THE DENSITY AND SPREAD OF SCOTCH BROOM

Scotch Broom is an invasive weed in many subalpine ecosystems. It often has substantial negative effects on ecosystem structure and functions. Decisions on optimal management strategies require predictions of the rates and patterns of Scotch Broom spread. This paper explores the environmental and management factors that influence the density and rate of spread of Scotch Broom in Barrington Tops National Park. The National Parks and Wildlife Services in a cooperative exercise with the State Forest prepared aerial maps showing Scotch Broom infestation in the Park for 1989 and 1999. These maps were used to generate data for the analysis. Map reference points 1km apart along the boundary of the 1989 area of infestation were examined and 1999 areas and densities were measured. Environmental factors measured include natural vegetation type, natural vegetation density, soil type, slope, altitude and the presence of private property or crown land. Areas of natural disaster, feral animal activity and National Parks and Wildlife Service management activities were also included in the analysis. We acknowledge the help of the NSW National Parks and Wildlife Service for providing us with the information and data for the analysis. Lack of data on rainfall at the specific map reference points is a possible limitation of the study. OLS, Probit and Multinomial Logit models were used to analyse different forms of the dependent variables measuring the density and the spread of Scotch Broom. The analysis shows that the treatments undertaken by the National Parks and Wildlife Services significantly reduce the spread of broom. In fact when this management is undertaken the probability of spread is reduced by 18.9% and on average treatment reduces the spread in kilometrs by 45%.