The spatial and temporal effects of fire on insect abundance in Mediterranean forest ecosystems

Among ecological communities, insects are important bioindicators of fire disturbance due to their sensitivity to environmental change and habitat requirements. In this study, we explored the relationship between insect abundance and distance from the ignition point of fires over a two-year period in an oak-dominated forest located in Southern Italy. Using 18 pitfall traps along three transects (running from the interior to the exterior of the burnt area), 2556 insect specimens belonging to eight orders and 26 families were collected. We used analysis of variance and developed a number of regression models to determine the spatial and temporal responses of insect abundance to fire. In addition, a comparison was made between terrestrial Coleoptera and Lepidoptera and the results were used to explain the effects of forest fire on different taxa. In terms of spatial variation, we observed a significant difference between abundance of Coleoptera in burnt (0–300 m) and unburnt (300–600 m) locations with the highest level of abundance in the forest at the edge of the burnt area. For Lepidoptera, differences were not as significant. In terms of temporal variation, we observed significant differences between the abundance of Coleoptera in the two study years, both in burnt and unburnt locations, with the highest level of abundance in the second year after fire. For Lepidoptera the temporal differences were also significant. The two insect orders showed a contrasting pattern in terms of mean abundance values: the abundance of Coleoptera increased during the survey period, while the abundance of Lepidoptera decreased. Fire disturbance influences the short-term response of insect abundance with positive or negative effects depending on the ecological traits and habits of taxa. Understanding these effects is crucial in highly-modified ecosystems, such as the Mediterranean forests.