Individual study: Responses of grass-layer beetles to experimental fire regimes in tropical savanna in Kakadu National Park, Northern Territory, Australia
Orgeas J. & Andersen A.N. (2001) Fire and biodiversity: responses of grass-layer beetles to experimental fire regimes in an Australian tropical savanna. Journal of Applied Ecology, 38
Up to 50% or more of northern Australian savannas are burnt each year, but the effects of these fires on savanna faunas are poorly known, especially for arthropods. The responses of grass-layer beetles to three fire regimes (unburnt; annual fires lit early during the dry season; annual fires lit late during the dry season) were investigated at Kapalga in Australia's Northern Territory. An attempt was also made to identify beetle species that might act as indicators of particular fire regimes.
Study area: The study was part of the Kapalga fire experiment located in Kakadu National Park, approximately 200 km east of Darwin, in Northern Territory, Australia.
Experimental design: Each experimental landscape compartment was a 15–20 km² catchment of a minor seasonal stream. Sampling occurred along transects running from the more poorly drained shallow sands of the stream margins, dominated by savanna woodlands, up-slope to the better drained loams supporting savanna open forest.
Three fire regimes or treatments were examined (each replicated three times) for their impact on grass-layer beetles:
i) early - compartments burnt annually early in the dry season (May/June)
ii) late - compartments burnt annually towards the end of the dry season (September/October)
Apart from some topographic and security constraints, treatments were assigned randomly. To minimize potential effects due to differences in fire history between compartments, fires were excluded for 18 months (1988–89) prior to the application of the fire treatments. Treatments were then applied for 5 years from 1990 to 1994.
Beetle sampling: A woodland and forest plot (each 40 × 20 m) was sampled in each compartment by sweep-netting (using 45cm diameter nets) during February (mid-wet season) and May (end of wet season) each year, from 1989 (18 months prior to fire treatments) to 1995. A sweep sample from each plot comprised the pooled catches of 100 sweeps, collected along five parallel transects (5 m spacing) of 20 sweeps.
Beetles were sorted and identified to species in the laboratory.
A total of 3,865 beetles comprising 233 species were recorded. The two dominant families Chrysomelidae (leaf beetles) and Curculionidae (weevils) contributed 91% of the total and 57% of species.
Abundance and richness: Total beetle abundance, species richness, family richness and the abundances of one of the 10 most common species were significantly affected by fire treatment. In all cases, beetle abundance and richness were similar in the two burning treatments, but greater than in the unburnt treatment. These differences were only apparent during the second half of the experiment. The responses were mirrored by changes in composition at species, family and guild levels.
Indicator species: Five beetle species appeared to be significant indicators of late fires, and one of early fires. However, these species were infrequently recorded and therefore of limited use for management. However, two common species were indicative of burnt habitats (early and late treatments).
Conclusions: Although there were significant effects of fire treatments on the beetle fauna, in the broader context of overall beetle dynamics, assemblages appeared remarkably resilient to fire. This may reflect a long history of association with frequent fire, and is consistent with many other components of the northern Australian fauna. The lack of effect of fire timing on grass-layer beetles calls into question management that focuses largely on fire intensity, and suggests that fire management needs to be more mindful of fire frequency.
Note: If using or referring to this published study, please read and quote the original paper. The original paper can be viewed at: http://www.blackwell-synergy.com/doi/abs/10.1046/j.1365-2664.2001.00575.x