Earthworms in past and present agricultural landscapes of Hebridean Scotland

Abstract

The Hebrides of Scotland constitute a unique set of island environments with a long history of human settlement and agriculture. Earthworm community surveys were undertaken in selected agricultural landscapes of Inner (Isle of Rum) and Outer (North and South Uist) Hebrides. On North Uist, earthworms were sampled from areas of Blackland (organic, anthropic, acidic agricultural soils) and on South Uist in machair (sandy, fertile, low-lying grassy pasture). Specific grassland and cultivated areas with various organic additions - including dung and seaweed - were targeted, using hand-sorting of soil for earthworms plus mustard vermifuge extraction. Work on Rum investigated earthworms in ridge and furrow (lazybed) agricultural systems, abandoned almost 200 years ago and since uncultivated, but grazed by ungulates. On the Uists, nine earthworm species were identified, representing all three ecological categories, but dominated by the epigeics, Dendrobaena octaedra and Lumbricus rubellus. Densities and biomasses across Blackland soils ranged from 10-130 ind. m−2 and 2.3–33.7 g m−2, respectively. Here, 5 species were present, and management had a significant effect on species richness and abundance with most earthworms present in recently restored lazybeds. In the machair soils, the corresponding measurements were 4–220 ind. m−2 and 0.8–89.0 g m−2. Significantly higher earthworm densities and biomasses were recovered below cattle dung pats compared with dung-free areas. Cultivated areas in machair were less diverse and had lower earthworm densities than uncultivated. On Rum, ridge and furrow abundances did not differ clearly with 24–102 and 34–112 ind. m−2 respectively and biomasses of 7.4–26.3 and 8.8–30.8 g m−2. Here, Aporrectodea caliginosa (49%), L. rubellus (23%) and Dendrodrilus rubidus (19%) dominated of the seven species found. Further research on earthworms in the Hebrides is warranted.