Effects of forest fire on ant diversity in the dry dipterocarp forest, Lai Nan Subdistrict, Wiang Sa District, Nan Province

Forest fire can have direct impacts on various organisms. Dipterocarp forests in Nan province have been consistently burned. However, the effects of the burning on ant diversity were insufficiently reported. This research investigated the effects of forest fire on ant diversity and compared ant communities between two habitats: burned and unburned dry dipterocarp forests. Ants were monthly collected from June 2010 to June 2011 using five methods: pitfall trapping, baiting, soil sifting, leaf sifting and hand sampling. The collected specimens were identified and classified into six subfamilies: Aenictinae, Formicinae, Ponerinae, Dolichoderinae, Pseudomyrmecinae and Myrmicinae. Fifty-three ant species, belonging to 30 genera, were identified. The mean of ant species diversity indices in the burned dipterocarp forest were significantly higher than unburned dipterocarp forest (p=0.032). The Sorensen’s similarity coefficient was at 79% between the unburned and burned dipterocarp forests. The mean of dominant indices in the unburned dipterocarp forest were significantly higher than burned dipterocarp forest (p=0.002). In unburned dipterocarp forest, the Shanon-Weiner’s species diversity index in the wet season (2.917) was higher than in the dry season (2.680), whereas in the burned dipterocarp forest, the diversity in the dry season was higher than in the wet season. The Sorensen’s similarity coefficient in the species composition between wet and dry seasons was highest in the unburned dipterocarp forest (82.9%). This pattern of species composition of ant indicated that the reservoirs could affect to the variation pattern in species composition between seasons in these areas. Afterwards, the ants were classified by their functional groups as dominant Dolichoderinae (DD), generalized Myrmicinae (GM), opportunists (OP), subordinate Camponotini (SC), hot/cold/tropical climate specialists (H/C/TCS), cryptic species (CS) and Specialist Predators (SP). Functional group analysis showed that both generalized Myrmicinae and opportunists were dominated in the burned area. GM had broad distribution patterns in relation to environmental stress and disturbance while the opportunists (Paratrechina) were largely unspecialized and submissive species. They showed a wide habitat distribution and were most abundant in habitats under stress or disturbance where other more dominant groups were limited. This approach allowed us to emphasize the ecological role of each species, reduce the ecological complexity on ant diversity and generate a predictable assessment tool of ant responses to fire disturbance. The dominance index in the unburned area was found to be higher than that in the burned area. The dominant species found in the burned dipterocarp forest was Odontoponera denticulata whereas weaver ant, Oecophylla smaragdina, dominated in the unburned area. The high similarity index between both areas suggested the similarity in vegetation structures and microhabitats. The results reveal that ant diversity in the burned dry dipterocarp forest has been recovering which may be caused by re-colonization of ecological succession and the new habitat characteristics.