Individual study: Use of wooden disks for non-destructive monitoring of soil surface invertebrates, Quail Island, Canterbury, New Zealand
Bowie M.H. & Frampton C.M. (2004) A practical technique for non-destructive monitoring of soil surface invertebrates for ecological restoration programmes. Ecological Management and Restoration, 5, 34-42
Monitoring of biodiversity is essential if the success of restoration goals and objectives is to be judged. Several aspects of terrestrial invertebrates render them as useful proxies of wider aspects of biodiversity. For example, invertebrates are amongst the most diverse taxonomic group and play a critical role in the functioning of ecosystems. One problem associated with monitoring invertebrates is that commonly used methods, such as pitfall or Malaise trapping, are lethal and therefore may be counterproductive to restoration. In this study, as an alternative to pitfall trapping, wooden discs were used as facsimiles for natural fallen logs, thus enabling non-destructive monitoring.
Study site: The study was undertaken on Quail Island, in Lyttelton Harbour (New Zealand) in an area of exotic grassland surrounded by native scrub under ecological restoration.
Wooden sampling disks: Wooden disks, 32-45 cm in diameter and 10-15 cm thick were cut from logs and dried. Four tree species (three exotic and one native) were used: pine Pinus radiate, macrocarpa Cupressus macrocarpa, oak Quercus sp. and the native black beech Nothofagus solandri. On 22 December 1999, eight transects, each consisting of four wooden discs, one of each disc type, placed 30 cm apart in a line in a randomized order on bare soil, were created around the perimeter of a 1200 m² patch of native scrub.
Invertebrate sampling: Invertebrate species occurring under the discs were recorded on eight occasions: 1 February 2000, 28 April 2000, 16 July 2000, 15 September, 16 November 2000, 15 Mar 2001, 1 July 2001 and 30 August 2001. Species diversity and numbers were calculated for each disc.
On 15 March 2001, beech disks hosted the lowest diversity and abundance of invertebrates compared with the other disk types. Pine discs had significantly more flatworms than other disk types. Only one flatworm was found under all beech disks during the entire duration of the study. Oak was favoured by harvestmen Nuncia obsesa grimmetti and Algidia cuspidate, with an average of 10 per oak disc found on 15 February 2001. However the numbers under different disc types were not quite significantly different. A full checklist of the taxa recorded under each disk type is given in Table 1 (attached).
Conclusions: Wooden discs provide a means of monitoring invertebrates in a non-destructive way, and may be useful in recording and monitoring of invertebrates not usually detectable by pitfall and Malaise trapping. Contrary to expectations, black beech, the only native species, was the poorest performing in terms of attracting invertebrates as a lower abundance and diversity were recorded, possibly due to the presence of toxic tannins in the wood. When monitoring invertebrates using discs, care must be taken in interpreting the data as the type of wood used to construct the discs can have a bearing on the species occurring underneath them.
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