Astron is often presented with very large project areas for weed mapping within a limited time frame. To map these areas efficiently, we often employ statistical methods to accurately determine the likelihood for weed occurrence over a large area at a minimal cost. The purpose of the Eastern Mines Weed Survey project was to identify and determine the distribution of weed species at selected monitoring sites and nearby reference sites.
A two-stage cluster sampling design was applied to each proposal area (the project area) and its surroundings (the reference area). A survey grid of 200 m x 200 m cells was applied to the area to be surveyed. Sampling sites were chosen in accessible locations where the risk of weed occurrence was thought to be greatest. Within each 200 m x 200 m cell two parallel 20 m x 200 m transects were surveyed for weeds. This sampling frame was viewed through the use of hand-held GIS devices. When field teams were unable to access monitoring sites, sites were easily moved to more accessible locations.
At the completion of the survey an inventory of weed species was compiled for the site. Astron also provided the client with maps, showing the likely occurrence of weeds across the project area. The data collected will enable us to determine whether or not future changes in weed levels within the project area can be attributed to the mine and its associated activity, a requirement of ministerial statement conditions for mining and infrastructure proposals. The use of statistical tools enables Astron to survey large areas and thus meet the weed management ministerial conditions for proposals in Western Australia at a minimal cost.