Grid-based sampling to identify areas being utilized by koalas in the South-east Forests of NSW

October 2007 – JULY 2008 The following maps provide a summary of results to date of an extensive koala survey that is being undertaken in the coastal forests between Bermagui and Tathra in South East NSW. The survey has focused initially on two areas. To the north is the Bermagui study area, which has a matrix of tenures, including freehold land, parts of the Bermagui State Forest, Bermagui Nature Reserve & Biamanga National Park. To the south, the Wapengo Study Area includes private land, parts of Mumbulla State Forest and Mimosa Rocks National Park. The survey project takes a partnership approach and now includes government agencies, indigenous organisations, educational institutions, and community groups and individuals. By fostering this partnership we hope to nurture a broad-based co-operative approach to koala recovery initiatives that will be assisted by the results of this survey program.

The survey method used is known as the regularised grid-based spot assessment technique (or GRIDSAT for short). This provides a simple, unbiased and robust sampling tool that records the presence/absence of koala evidence (koala faecal pellets) at each intersection of a 500m grid under 30 live trees over 150mm diameter at breast height. Where more intensive sampling is warranted, the intervening plots (350m apart) are also sampled.

The GRIDSAT also enables a measure of activity to be recorded, determined by the proportion of trees with koala evidence compared with the total number of trees sampled. This measure of koala activity is shown on the maps; the larger the dots, the greater the activity level. Interpolation of activity data using a combination of regularized splining and contouring enables the boundaries of koala activity cells to be delineated. Using this assessment method, 293 field sites have thus far been sampled to effectively blanket areas of 3,100ha in the north, and 3,350ha in the south. Koala activity was recorded in 37 sites overall, with a median activity level of 10% (range: 3.33% – 16.67%). Koala activity was twice as common in the Wapengo area as it was in the Bermagui study area. Evidence gathered from the Wapengo study area is encouraging, with activity cells spread between its northern and southern boundaries and several breeding females, as evidenced by the presence of small and large koala faecal pellets of consistently different sizes, recorded within these activity cells. Conversely, the evidence gathered in the Bermagui Study Area, when compared with historical records from the past five decades, suggests a concerning decline. The survey is still in its early stages. We estimate that there are approximately 11,500 ha of potential koala habitat that should be assessed before the distribution and abundance of the population of Koalas in the coastal forests between the Bega River and Wallaga Lake can be clarified and appropriate baseline data established. In a complementary study, DECC has funded scientists from the Australian National University to assess the eucalypt leaf nutrient/phenolic levels of koala browse species across the broader study area. This may help identify areas sustaining better quality browse and prioritise locations where the grid-based assessment should be undertaken. It may also provide information on whether forest management activities influence the quality of browse. This study is still under design and it is not expected to commence until late 2008.