Woodland Restoration on Landfill Sites: Earthworm Activity and Ecosystem Service Provision

Abstract

The addition of composted greenwaste (CGW) into soil-forming materials during land reclamation may improve tree growth, alleviate certain negative soil properties and provide an effective waste management solution. CGW addition may also assist the establishment of sustainable earthworm populations, which in turn can further aid soil development through their burrowing and feeding activities. Despite these potentially mutual benefits, little research exists into CGW and earthworm interactions with trees on reclaimed land, and the aim of this thesis was to investigate such interactions. A large-scale field experiment and a nursery-based mesocosm experiment revealed the responses of the tree species Italian alder (Alnus cordata) and Norway maple (Acer platanoides) to CGW and earthworm addition in reclaimed soil. Findings revealed a synergistic effect of CGW addition and earthworm activity leading to significantly greater A. cordata and A. platanoides growth. CGW addition significantly increased levels of soil organic carbon and essential plant macro-nutrients, with earthworm activity increasing the accumulation of organic carbon into reclaimed soils. Additional laboratory-based research revealed the performance of four common UK earthworm species in reclaimed soil, and demonstrated that CGW can support earthworm establishment, and that the earthworms Aporrectodea longa and Allolobophora chlorotica are particularly suitable candidates for inoculation to reclaimed soil. These two earthworm species showed a preference for the foliar material of A. cordata over A. platanoides, but after two weeks, microbial degradation of leaf litter increased A. platanoides leaf palatability to these earthworms. These two tree species may therefore be capable of supporting earthworm populations on reclaimed landfill. A survey of a newly reclaimed site showed that natural colonisation of reclaimed land by earthworms can occur rapidly (within 2 years), where soil quality is sufficient and legacy soil materials are stockpiled and applied following best practice guidance. The studies in this thesis demonstrate methods for effectively improving woodland establishment and soil quality on reclaimed landfill, through CGW application and earthworm activity promoting soil development and encouraging tree growth.