Y. Capowiez et al., Evolution of burrow systems after the accidental introduction of a new earthworm species into a Swiss pre-alpine meadow, BIOL FERT S, 31(6), 2000, pp. 494-500
The unintentional introduction of a new earthworm species (Aporrectodea noc
turna) into a Swiss pre-alpine meadow resulted in a great increase in earth
worm density in the newly colonized area (386 m(-2)) compared with the dens
ity observed in the natural area (273 m(-2)) where an earthworm community w
as already present. To investigate the impact of this introduction on the b
urrow systems, eight soil cores (length 25 cm, diameter 16 cm) were taken (
four in the colonized area and four in the natural area) and analysed with
computer-assisted X-ray tomography. The resulting images were processed to
obtain the 3D-skeleton reconstructions of the earthworm burrow systems. Due
to high variability in these burrow systems, only slight differences were
observed between the two areas. The total burrow length and the mean burrow
lengths tended to be greater in the colonized area. Moreover, the distribu
tion of pore numbers with depth showed different patterns with a maximum fo
r depths between 10 cm and 15 cm in the colonized area and a maximum for de
pths between 20 cm and 25 cm in the natural area. These differences may hav
e been related to: (1) the particular behaviour of A. nocturna, which was o
bserved to cast at the surface in this site, and (2) the predominance of ju
venile earthworms around the colonization front. These differences were suf
ficient to create significant effects on the continuity of the burrow syste
ms (assessed by the number of different pathways between virtual horizontal
planes) for the two areas. The colonized area was characterized by a great
er pore continuity, which could have resulted in enhanced transfer properti
es.