Mature exotic conifer stands have greater catches of the EU-protected Geomalacus maculosus than adjacent peatland or clear-felled stands—implications for forestry

Mature exotic Sitka spruce (Picea sitchensis; Bong. Carrière)-dominated stands, particularly trees of greater circumference, result in greater numbers of Geomalacus maculosus (Allman) captures than adjacent clear-felled stands and adjacent peatland with Before-After-Control-Impact-Paired analysis indicating lower catches of G. maculosus post-felling.

Context. The discovery of EU-protected Geomalacus maculosus in commercial plantations requires an understanding of the implications of forestry practices for the species within the context of sustainable forest management.
1. Compare Geomalacus maculosus captures across mature exotic Sitka spruce-dominated stands, previously clear-felled stands and adjacent peatland habitats.
2. Assess the suitability, for forest managers, of population estimate models for G. maculosus.
3. Assess the implications of felling by comparing relative abundances of G. maculosus directly before and after clear-felling at a mature exotic Sitka spruce-dominated stand.
Methods. Geomalacus maculosus catches were compared at four sites across two to three mature (43–45 years old) conifer stands per site, one clear-felled stand per site, and one adjacent peatland per site using refuge traps and hand searching. Capture-mark-recapture studies were undertaken to estimate population sizes. A BACIP (Before-After-Control-Impact-Paired) analysis was undertaken in one forest stand at one forest site to determine impacts of a clear-felling event.
Results. Mean catches of Geomalacus maculosus adults in the mature forest stands were over 10 and 11 times greater than mean catches on peatland and clear-fell stands, respectively. The Schnabel model for estimating population size was most suited for mature forest stands but could not be utilised for the other habitats. BACIP analysis showed a significant impact of clear-felling with a 95% reduction in mean G. maculosus catches after a clear-felling event where none of the individuals marked prior to felling were recaptured compared to 21% recapture rates at the control site. Greater tree circumference in mature conifer stands correlated with greater catches.
Conclusion. Guidelines are needed to ensure the protection of Geomalacus maculosus in commercial forestry. Interventions could include patch/tall stump retention at final felling and/or translocation of the protected species.

Conservation, Capture-mark-recapture, Population estimates, Before-After-Control-Impact-Paired (BACIP), Slug

Johnston, E., Kindermann, G., O’Callaghan, J. et al. Annals of Forest Science (2018) 75: 4.

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