Distribution and abundance of burrows formed by Lumbricus terrestris L. and Aporrectodea caliginosa Sav. in the soil profile

The distribution of burrows made by Lumbricus terrestris L. and Aporrectodea caliginosa Sav. was studied on an unploughed field. The positions of earthworm burrows were mapped in 9 horizontal planes to a depth of 80 cm in a pit of 70 by 40 cm. Burrow diameter and presence of plant roots growing in burrows were also recorded. Burrows on six of the nine planes were considered as two-dimensional point patterns and analyzed as spatial point processes. A three-dimensional image was constructed for burrows formed by L. terrestris. The total number of burrows ranged between 180 and 1260 m−2 at depths of 80 and 30 cm, respectively. The majority of burrows were evidently formed by A. caliginosa. The smallest size class (2–3 mm) of burrows was dominant at depths between 8 and 40 cm. Deeper in the soil profile, the proportion of larger burrows increased markedly. Burrows formed by L. terrestris appeared to be non-branching, and extended vertically beyond 80 cm. In all soil layers studied, burrow distribution was found to be completely random. The proportion of burrows containing plant roots was between 18 and 60%, at depths of 80 and 15 cm, respectively.