Evolution of earthworm burrow systems after inoculation of lumbricid earthworms in a pasture in the Netherlands

In 1983, an earthworm-free pasture was inoculated with four earthworm species. The earth-worms dispersed with an average velocity of 6.3 m y−1. In 1991, four burrow systems, ranging in age from 0.6 to 7.3 y, were mapped three-dimensionally to establish the development of these systems. Aporrectodea longa was the fastest colonizer, while Lumbricus terrestris dispersed slowly. The abundance of earthworms peaked at 4.1 y, after which it dropped to a lower level. The density of the burrow systems followed a similar pattern. The net burrow creation rate reached a maximum of 110 mm−2y−1 between 0.6 and 0.9 y. The burrow systems had a highly vertical orientation which increased with age. The density of branched burrows relative to the total system has its maximum in the youngest system and declines with age. The burrow systems continued to deepen after the maximum density had been reached.