National Weeds Program Impact of Environmental Weeds on Biodiversity: a Review and Development of a Methodology

FOREWORD The impact of environmental weeds on the natural environment is an area that has been little studied in Australia. More often than not, impact is assumed rather than quantified. If the impact of environmental weeds on nature conservation values is not quantitatively assessed before a control program is begun, valuable resources can be wasted. For instance, how would it be possible to determine the level at which the weed invasion has a negligible impact on the natural environment? This is a critical question when you are considering investing resources towards the control of environmental weeds. Key questions that need to be asked before control programs are undertaken for environmental weeds include determining the impact of weeds on native species and ecosystem functions, the threshold densities at which there is little or no impact of the weed on conservation values, and what factors can be manipulated to reduce that impact. This report reviews the impact of environmental weeds on biodiversity values and assesses the techniques used in various quantitative studies. It provides a standardised methodology incorporating experimental design and data analysis options that address the above questions. This publication is a comprehensive document providing excellent material for future research and planning for environmental weed management. It is an invaluable contribution to the area of impact assessment and I hope it will be considered an important tool for use by all agencies and individuals concerned with biodiversity conservation.