A novel research project at the ECN site Alice Holt forest yields valuable distribution records for the UK’s rarest earthworm species.

Current UK earthworm distribution records indicate some species as rare or very rare; however it may instead be the case that their typical habitats are simply under-sampled. To date, much UK earthworm-related research and surveying has focused on agricultural land, and where forest habitats are sampled, important microhabitats (e.g. dead wood) are often overlooked by standard sampling methods (Schmidt et al., 2015). Undertaking micro-habitat surveying alongside traditional sampling in forest habitats may reveal a wealth of new information on earthworm species distributions and their ecology.

A research project is underway which is developing a systematic method for sampling forest deadwood for earthworms, using a subset of the ECN vegetation plots at Forest Research's Alice Holt forest, Surrey, (Benham et al. 2012) as a case study. Fieldwork was conducted in November 2017 by Frank Ashwood, and involved standard earthworm soil pit sampling, as well as sampling underneath deadwood bark and in soil underneath deadwood.

Surprisingly, the earthworm data yielded three new records of the nationally very rare earthworm species Denbrobaena pygmaea - a new species record for the Vice County of North Hampshire, and boosted the national records of this species from six records to nine (The National Earthworm Recording Scheme, 2018).

D. pygmaea is a small species, averaging 20-35 mm in length, and current UK distribution records show D. pygmaea as limited mainly to the south of England, with an additional record from the East Midlands. At present, our understanding of the habitat preferences of this species includes well-drained soil, moist litter and mossy banks of streams in deciduous woodlands (Sims and Gerard, 1999), and now also includes clayey soil beneath decaying wood.

This finding demonstrates that, through increased woodland sampling and sampling a variety of habitats, we may fundamentally change our understanding of earthworm species distributions and ecologies. Additional earthworm species findings from Alice Holt forest will be reported when this research is published later this year.

 

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