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| Anonymous, | |
| Rapid Survey of the PT. Asiatic Persada / PT. Asialog Oil Palm / Forest Matrix by the Zoological Society of London | |
| 2006 Full Book | |
Between February and April 2005 an extensive survey of medium/large mammal distribution was conducted throughout 900km2 of PT Asiatic Persada (an oil palm concession) and PT Asialog (a logging concession), primarily to determine whether tigers still existed in the landscape following the fall in encounters reported in the plantation concession (ZSL 2004). The survey was conducted using 36 3x3 km foot transects across four habitat types to search for tiger and other wildlife sign supported by camera traps. Surveys were repeated to calculate measures of detectability for individual species which were then used to calculate the proportion of the study site occupied by each species. 1296 man-hours were spent searching for wildlife, recording 1362 independent 'encounters' (primarily animal tracks). 20 cameras were deployed in 71 positions for a total of 860 trap nights, recording 1102 subjects, 63% of which were wildlife or people. In total 28 terrestrial mammal species were recorded, as well as 5 primates and 2 endangered bird species. Tiger were shown to be still present, as were elephants, but cameras only showed evidence of three individual tigers, none of which were individuals that had previously been recorded within the plantation. No species was detected on every survey repeat, showing the importance of using repeated surveys. Consequently, adjusted estimates of 'true' occupancy were higher than the na‹ve estimates obtained from a single survey. The results showed tigers occupy less than 10% of the landscape, despite 90% of the area being suitable. Prey levels appeared healthy, with sambar and muntjacs estimated to occupy nearly 90% of the area and wild pigs occupying 100%. Occupancy estimates were more precise for the more detectable species (tigers, deer, tapir and various small mammals). Evidence of humans was high, with settlements and illegal logging occurring in over 80% of the landscape. There were insufficient transects to accurately model the effect of the most important explanatory factors on occupancy of most species, however interpolating encounter rates on GIS showed that, with the exception of wild pig, all species tended to prefer the forest habitat. Even species that occurred within oil palm such as civets and leopard cats appeared to be more common in the forest. Land within the oil palm concession was still used by species of conservation interest, including sun bears, tapir and dhole, although only in the unplanted areas. However, compared to previous years, evidence of species in either of the plantation 'conservation' areas was very low. Tigers were shown to occur in two areas of the forest, one of which also showed high levels of human disturbance and is not included in the new conservation-focussed 'restoration area' land classification. The survey therefore showed that tigers and other species of conservation concern still existed in the commercially-dominated landscape but that the role of the oil palm plantation concession as species habitat was greatly reduced compared to previous years, probably due to large increase in human activity in the set aside conservation areas. However, the low occupancy levels show the local tiger population was in extremely poor shape and occupying a fraction of the area previously though to be occupied. Distribution of key prey species suggest prey availability was not a key concern leaving direct human activity (poaching or land disturbance) as the more likely reasons. The survey was also a key step in the development of rapid survey methods. Key points learned were the importance of repeated surveys, their suitability for more detectable species, and the need for large sample sizes to allow modelling of likely explanatory factors. These points will be incorporated into further rapid surveys to be conducted at the same and additional sites in the future. |
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