Improving the landscape scale management of Buffel Grass Cenchrus ciliaris using aerial survey, predictive modelling, and a Geographic Information System

Abstract

Buffel Grass Cenchrus ciliaris is a major environmental threat to biodiversity in central Australia and is rapidly expanding its distribution on National Parks and other areas of conservation concern. Managers need appropriate mapping of the potential and current Buffel Grass distribution at a broad landscape scale in order to prioritize their use of limited resources for survey and control efforts. Watarrka National Park was used as a case study to trial the effectiveness of aerial survey for mapping Buffel Grass distribution. Over 7 000 aerial observations were recorded from transects across the whole Park. Ground truthing indicated an acceptable level of accuracy for the aerial derived data at 84%, and a Kappa coefficient of 49. The aerial survey data were used to build a surface probability model for the entire Park based on environmental variables using Generalized Linear Modelling and then applied using a Geographic Information System. Distance to drainage and distance to tracks, followed by ruggedness, hummock grass cover and soil texture were the most important explanatory variables in determining the probability of occurrence of Buffel Grass. The surface model was overlaid with available vegetation mapping to quantify the level of threat to native plant diversity, in particular rare plant species diversity. This information is useful in developing a strategy for managing Buffel Grass at a landscape scale that is based on invasive potential and known biodiversity values, where previous management has focused on small scale site specific control actions.