Applied Soil Ecology 73 (2014) 130–133 Contents lists available at ScienceDirect Applied Soil Ecology journa l h om epa ge: www.elsevier.com/locate/apsoil Short communication Slow recovery of earthworm populations after heavy traffic in two forest soils in northern France N. Bottinelli a,b,∗ , Y. Capowiez c , J. Ranger a a INRA, UR1138 INRA, Biogéochimie des Ecosystèmes Forestiers, F-54280 Champenoux, France b State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, CAS, Nanjing 210008, China c INRA, UR 1115 Plantes et Systèmes Horticoles, Domaine Saint Paul, 84914 Avignon Cedex 09, France a r t i c l e i n f o Article history: Received 9 April 2013 Received in revised form 26 August 2013 Accepted 30 August 2013 Keywords: Soil compaction Earthworms Recolonisation a b s t r a c t To determine the role of earthworms in regenerating compacted zones, it is essential to consider their capacity to colonise these zones. This study aimed to determine the short-term (3–4 years) response of earthworm populations to heavy traffic in two forest soils, at Azerailles (AZ) and Clermont-en-Argonne (CA) in north-eastern France. Earthworm populations were recorded immediately and for 3–4 years after heavy traffic by a 8-wheel drive forwarder with a load of about 23 Mg at AZ and 17 Mg at CA. To test the capacity of earthworms to recolonise traffic plot from the edges, an extra sampling was performed at the border of the traffic plots at AZ. Heavy traffic had a detrimental impact on the density and biomass of three earthworm functional groups. At AZ, earthworm populations, dominated by endogeic species, followed by anecic and epigeic species, had not fully recovered four years after compaction. The absence of statistically significant colonisation by the three functional groups from control to traffic plots indicated that the soil habitat was not yet favourable. At CA, earthworm populations, represented exclusively by epigeic species, had fully recovered three years after compaction, suggesting that the soil habitat was already suitable for them. This strong dependence on soil habitat quality is discussed and may be one reason for variation in the recovery rate of earthworms after compaction reported in the literature. In conclusion, this study did not support the hypothesis that earthworms play a role in regenerating soil structure the first few years following forest-soil compaction. © 2013 Elsevier B.V. All rights reserved. 1. Introduction The growing mechanisation of forest operations is increasing soil compaction, resulting in degradation of soil structure and soil functioning (Greacen and Sands, 1980; Horn et al., 2004). In for- est ecosystems, the remediation of compaction by tillage is rarely used, being difficult to apply due to the presence of stumps and large roots. Therefore, compacted forest soils must recover their structure through natural processes (i.e., wetting–drying cycles, freeze–thaw cycles during winter or biological activity) (Greacen and Sands, 1980). Among the main biological regulators of soil structure in tem- perate regions are earthworms, often called “soil engineers” due to the importance of their burrowing and casting activity to soil structure (Lee and Foster, 1991; Jouquet et al., 2006). It is generally claimed that earthworm activities contribute to the regeneration ∗ Corresponding author at: Agriculture, Institute of Soil Science, Chinese Academy of Sciences, 71 East Beijing Road, Nanjing 210008, China. Tel.: +86 25 8688 1198; fax: +86 25 8688 1000. E-mail address: nicobottinelli86@hotmail.com (N. Bottinelli). of compacted zones, and it is well-documented under controlled conditions where earthworms are forced to move through com- pacted zones (Langmaack et al., 1999; Larink et al., 2001; Capowiez et al., 2009; Jouquet et al., 2012; Müller-Inkmann et al., 2013). Few, however, have validated this role in the field (Capowiez et al., 2012). Because soil compaction is a physical disturbance that leads to a decrease in earthworm populations (Söchtig and Larink, 1992; Jordan et al., 1999; Althoff et al., 2009; Capowiez et al., 2012), the regeneration of soil structure by earthworms ini- tially should depend on their capacity to colonise these zones. The colonisation of new environments by earthworms has been exten- sively studied (reviewed in Eijsackers, 2011). Even if in this review, soil bulk density was indicated as a limiting factor for colonisa- tion, very few studies have investigated the natural recovery of earthworm populations after heavy traffic. Moreover they have produced inconsistent results, with full recovery of earthworm abundance varying from a few months to several years (Jordan et al., 1999; Althoff et al., 2009; Capowiez et al., 2012). Two experimental sites were set up in two temperate forests in north-eastern France to monitor changes and recovery in physical, chemical and biological properties following traffic by a full-loaded forwarder (Goutal et al., 2012a,b; Goutal et al., 2013). In the initial 0929-1393/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsoil.2013.08.017