Seasonal patterns in abundance, species richness and assemblage composition were also evident. Species richness peaked in January, while abundance peaked in February. Different species showed different seasonal peaks and troughs, including species with winter peaks. The sampling cycle coincided with an initial pulse in abundance of saproxylic beetles, with sample-intensity-corrected summer peaks in abundance decreasing by a factor of four over the five summers sampled. The time-lag between felling and trap fitting did not noticeably influence this pattern. However, the height of the summer abundance peaks was related to the date of felling: those felled in autumn had more individuals emerging in the first three summers, while those felled in summer had more individuals emerging in the latter two summers. Different species showed different patterns in the degree and direction of their annual peaks over this period. While the peaks of many declined over the cycle, those of others increased or reached a maximum mid-way through the cycle.

Each species was categorised by its likely ‘saproxylicity’, mode of dispersal, feeding guild membership and microhabitat preferences. Obligately saproxylic species were more numerous than facultatively saproxylic species; species able to disperse by flight were much more numerous than crawlers; predators comprised the most abundant feeding guild; and there were roughly equal numbers of litter/surface dwelling and log interior-dwelling species. While the lower collecting bottles tended to preferentially sample ‘crawlers’ and the upper collecting bottles ‘fliers’, the capture of many individual species did not fit this pattern.

Species richness and abundance were positively correlated. Overall, mature logs yielded 26% more individuals and 30% more species than regrowth logs. However, there was so much variation among samples that there was no clear tendency for samples derived from a larger log volume or surface area to yield more individuals. This obviated the need to standardise sample size by volume or surface area – a process which generated nonsensical rates of species accumulation in regrowth logs. Standardising sample size instead by the number of individuals made little difference to the results of analyses of assemblage composition. These analyses consistently suggested that there were significant differences between mature and regrowth logs. Many of the twenty commonest species showed distinct ‘preferences’ for either mature or regrowth logs; some of these preferences could only be picked up in analyses that also considered sample season.

The findings from this study do not on their own point to mature logs being dramatically different from regrowth, but some subtle differences are evident. In combination with other studies (locally and elsewhere) they do suggest that both mature and regrowth logs support a rich saproxylic beetle fauna. They further suggest that a future forest lacking mature logs might not be able to support some saproxylic beetle species, including species whose close relatives in the more highly managed European forests are now on the verge of extinction.

Meanwhile, a related project has studied saproxylic beetles and fungi in logs in an intermediate decay stage.

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Grove, S. & Forster, L. (2011). A decade of change in the saproxylic beetle fauna of eucalypt logs in the Warra long-term log-decay experiment, Tasmania. Forestry Tasmania Technical Report, Hobart.

Grove, S.J. & Forster, L. (2011). A decade of change in the saproxylic beetle fauna of eucalypt logs in the Warra long-term log-decay experiment, Tasmania. 1. Description of the fauna and seasonality patterns. Biodiversity and Conservation 20: 2149-2165.

Grove, S.J. & Forster, L. (2011). A decade of change in the saproxylic beetle fauna of eucalypt logs in the Warra long-term log-decay experiment, Tasmania. 2. Log-size effects, succession, and the functional significance of rare species. Biodiversity and Conservation 20: 2167-2188.

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Grove, S., Bashford, R. & Yee, M. (2009). A long-term experimental study of saproxylic beetle (Coleoptera) succession in Tasmanian Eucalyptus obliqua logs: findings from the first five years. Chapter 6 in: Fattorini, S. (Ed.), Insect Ecology and Conservation. Research Signpost, Kerala, India, pp. 71-114.

Wardlaw, T., Grove, S., Hopkins, A., Yee, M., Harrison K. & Mohammed, C. (2009). The uniqueness of habitats in old eucalypts: contrasting wood-decay fungi and saproxylic beetles of young and old eucalypts. Tasforests 18: 17-32.

Yuan, Z.-Q. (2000). Long term monitoring of log decay in old growth forest at Warra (a summary report on initial establishment of the study). University of Tasmania, Hobart.