RECLAIMING LANDFILL TO WOODLAND USING TREES, EARTHWORMS, AND COMPOSTED GREEN WASTE

Abstract

Composted green waste (CGW) is a general-purpose organic soil amendment made from plant and food waste. Over the last 25-years, field trials have been conducted on reclaimed land throughout the UK, to understand CGW influence on tree growth and soil development during restoration. These trials found CGW increases tree growth and soil organism activity by supplying organic matter, nutrients, and provides other physical, chemical, and biological benefits. However, this knowledge has been based exclusively on short-term data obtained during the first 2 to 4-years of woodland establishment. To resolve this, the present study revisited historic field experiments to examine CGW impacts on the long-term recovery of woodland ecosystems. Tree growth, soil formation, nutrient cycling, and carbon storage were assessed to evaluate CGW impact on supporting and regulating ecosystem services. Similarly, earthworm populations were also recorded as their activities mediate these ecosystem services. Data revealed one-off application of compost has short acting and longer acting ‘legacy effects’, that remained detectable at sites reclaimed 5, 10, and 20 years ago. When sufficient quantities of CGW are used the ‘compost-effect’ is clear and consistent, lowering soil C:N, and increasing nitrogen stocks, soil organic matter content, and soil carbon storage. During the first 5 years of site development, ground-vegetation, earthworms, and CGW drive soil formation, nutrient cycling, and carbon storge. Then, as restoration progresses the influence of trees grows coming to dominate site and soil development. Of the trees species studied, Italian Alder (Alnus cordata) and Silver birch (Betula pendula) are compatible with CGW. Their fast growth and high-quality litter compliments’ the fertile soil conditions compost and earthworms create. Yet, the fertile conditions CGW creates may not be suitable for all trees and restoration contexts as evidenced by CGW’s chemical properties and general profile. Indeed, organic amendments, trees, and soil organisms should be conceptualised as complementary integrated parts of a broader ‘reclamation system’, where components interact with one another and their surrounding ecological conditions. The elements of a reclamation system must be compatible with one another and can be adjusted or replaced depending on site conditions and project goals.