Establishment of earthworms on reclaimed lignite mine soils in east Texas

Little is known about earthworm establishment after surface mining of lignite coal in continental climates such as the south central region of the United States. This study examined the abundance and species composition of earthworms in afforested lignite coal mine soils in east Texas. In a 3 × 3 × 2 factorial design, earthworms were sampled under two methods of land reclamation, haul-back (n = 30) and mixed overburden (n = 30). The study was conducted on a chronosequence of 2-28 years since afforestation under pine plantations and mixed pine and hardwood stands. The fieldwork was conducted from January 2012 through March 2014 using hand-sorting field methods. Forest cover type was significant at the mixed overburden sites (p = 0.0128); mixed pine and hardwood forest soils (13.7 ± 25.46 ind. m−2) contained 43% more earthworms than pine plantation soils (7.6 ± 17.06 ind. m−2). The number of earthworm individuals was significantly lower in 2-8 year-old stands than in 12-18 and 22-28 year old stands (p < 0.0001) at both haul-back and mixed overburden sites. Regression analysis found percentage of silt to positively influence earthworm abundance. Analysis of the species composition at both Beckville and Oak Hill mines revealed that 83% of earthworms were native earthworms species (from the genera Diplocardia and Bimastos) and 17% were exotic species (Aporrectodea trapezoides, Microscolex dubius, Lumbricus rubellus and Octolasion tytaeum).