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A 2 mm long scydmaenid beetle - a typical sized member of a family of beetles that is common in forest litter. |
Image: Sue Baker |
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Project summary:
The ecological effects of clearfell harvesting followed by high intensity regeneration burning are sometimes thought to mimic wildfire, the natural disturbance regime in Tasmanian wet forests. This project examined whether the litter-inhabiting beetle populations in logging regeneration forest approximated those in wildfire regeneration forest. Three pairs of adjacent 33-year-old logging and wildfire regeneration sites were selected in the Arve River Valley.
A grid of nine plots was established at each site; four pitfall traps at each plot collected litter beetles over a 30 day period in late spring – early summer. A large number of habitat variables were measured at each plot: soil bulk density, organic carbon content and pH, make up and complexity of the litter layer, surface temperature conditions, % canopy cover, basal area and species composition of trees, numbers of logs, plot slope and aspect. In total, 6,128 beetles were collected, representing 204 morphospecies in 26 families.
Differences between regeneration types were tested using Analysis of Variance (ANOVA), based on the species richness and abundance of common beetle families and sub-families, the abundance of the 29 most common morphospecies, and the degree to which the fauna was dominated by the most common species. The beetle populations in wildfire and logging regeneration could not be distinguished. However, beetle populations did differ between sites. The Aleocharinae and one carabid species were more abundant and had higher species richness at one of the three site pairs, and the beetle fauna was also less dominated by the most abundant species at this site.
Environmental factors considered susceptible to logging impacts were not different between wildfire and logging regeneration forest. Pattern analysis indicated a certain degree of separation of the study sites based on their beetle fauna, with reasonably distinct clusters of logging and wildfire regeneration plots at the site pair highlighted as different in the ANOVAs. A number of different beetle families and morphospecies were important in defining major clusterings of plots. Multiple regressions of the abundance and species richness of beetle families and morphospecies with environmental variables gave fairly low explanatory value (adjusted R2 = 0.36), with few of the many habitat variables measured providing substantial contribution to explanation of the beetle distributions.
The percentage canopy cover and understorey plant cover, the proportion of rainforest tree species in the canopy, the covering of dead manfern fronds and of the O2 organic litter horizon, and the organic carbon content of the soil were the factors most strongly correlated with the beetle distributions. There have been some changes to logging practices in the 30 or so years since the study sites were harvested which might have negative impacts on litter beetles in the future; fewer trees are now left standing in coupes and fewer logs left on the ground.
This may result in less diversity of canopy cover conditions resulting from windthrow of old-growth trees, and a diminished rotting log resource, both of which are known to influence litter beetles. While this study did not find any differences between the litter beetle assemblages in logging and wildfire regeneration, it does not necessarily demonstrate that the logging impacts mimic those of the natural wildfire regime. Natural wildfires occur on different spatial and temporal scales than harvesting, and are likely to result in a greater diversity of habitat; beetles may be susceptible to these factors.
Methodology: Three pairs of adjacent 33-year-old logging and wildfire regeneration sites were selected in the Arve River Valley.
A grid of nine plots was established at each site; four pitfall traps at each plot collected litter beetles over a 30 day period in late spring – early summer.
A large number of habitat variables were measured at each plot: soil bulk density, organic carbon content and pH, make up and complexity of the litter layer, surface temperature conditions, % canopy cover, basal area and species composition of trees, numbers of logs, plot slope and aspect.
Differences between regeneration types were tested using Analysis of Variance (ANOVA), based on the species richness and abundance of common beetle families and sub-families, the abundance of the 29 most common morphospecies, and the degree to which the fauna was dominated by the most common species.
Datasets: None available.
Publications: Baker, S.C. (2000). Forest litter beetles and their habitat: a comparison of forest regenerated by wildfire and logging practices. Honours thesis, University of Tasmania, Hobart.
Baker, S.C., Richardson, A.M.M., Seeman, O.D. & Barmuta, L.A. (2004). Does clearfell, burn and sow silviculture mimic the effect of wildfire? A field study and review using litter beetles. Forest Ecology and Management 199: 433-448.
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