Effects of two short rotation prescribed fires in spring on surface-active arthropods and earthworms in dry sclerophyll eucalypt forest of west-central Victoria

Abstract

Summary The effects of two prescribed low intensity fires (from 137 to 209 kWm−1) within three years on invertebrates in litter/upper soil were assessed in dry sclerophyll eucalypt forest near Daylesford in west-central Victoria. The 5.9 year study was based on 65 210 arthropod specimens representing 34 ordinal or lower level taxa contained in 2 300 pitfall trap samples, and on in situ counts of earthworms (Annelida) in 2 120 litter/upper soil samples, from a twice burnt site and an unburnt “control” site within a 31.3 ha area. The two fires had no discernible effect on total arthropods, total non-insects, total insects and total arthropod decomposers, though activity of total predators increased significantly after the second fire due largely to the Dermaptera (earwigs). A reduction in activity, up to one year, was recorded after each fire for the commonly trapped Collembola (springtails). Earthworm populations also declined substantially, but recovered to “control” levels within three years of each fire. Activity of the Coleoptera (beetles) was significantly lower after the second fire compared with the first, but there was no difference in activities after the first and second fires relative to the respective pre-fire levels. The Diptera (flies) recorded a drop in activity during winter following the first fire only, and effects other than fire are believed to be the cause. As Collembola and earthworms are major decomposers of forest litter, it appears that two consecutive fires in spring may interrupt the decomposer cycle for up to three years. The effect of fire on the Coleoptera remains uncertain, as levels of activity had declined simultaneously on both the burnt and “control” sites, and it is not known whether this trend was caused by many or few beetle taxa. The practical implications of the results are that any fires prescribed in spring should be applied at intervals of more than three years (and outside protracted drought periods), to minimise adverse effects on the general invertebrate fauna, and on Collembola and earthworms in particular, within litter/upper soil of the type of dry sclerophyll eucalypt forest studied.