Above and Belowground Ecological Linkages in Temperate Forest Soils

Abstract

Forests worldwide are an integral part of humanity’s natural capital in which stocks of natural assets generate ecosystem services that enhance the welfare of humans. These natural resources are crucial for accommodating a diverse range of species and regulating the climate, cycling nutrients, and supporting human livelihoods by providing a sustainable flow of goods and services. However, the loss of forest cover globally poses severe threats, including significant biodiversity loss, as forests are home to over 80% of terrestrial species. Deforestation and forest degradation, primarily driven by agriculture, leads to habitat fragmentation and diminished biodiversity, increased carbon emissions, and the degradation of land, which intensify the negative effects of climate change and threaten the well-being of both human and natural systems. Global efforts to increase forest cover through reforestation and afforestation are crucial strategies to tackle these environmental challenges. However, these initiatives sometimes overlook the complex processes occurring belowground, which are vital for the long-term health and stability of forest ecosystems. Soil biodiversity and the interactions within soil communities play critical roles in nutrient cycling, water retention, and overall ecosystem resilience, factors that must be considered to ensure the success and sustainability of forest restoration efforts. This thesis explores the complex relationships between the aboveground and belowground components of temperate forest ecosystems. It specifically examines the impact of woodland creation and maturation on soil sustainability and the overall health of the ecosystem. Throughout this thesis I use a chronosequence of woodland creation sites (20-160 years), comparing them to ancient woodland (250+ years) and adjacent pasture sites to investigate the mechanisms involved in soil carbon storage and the dynamic interactions within the rhizosphere. This includes the study of fine root morphology, microbial communities, earthworm populations, and soil physico-chemical properties to understand the impact of forest development and the transformation of agricultural land into woodlands on soil carbon stocks and biodiversity. I demonstrate that woodland sites store more soil organic carbon than neighbouring pastures, with old-growth forests showing a fourfold increase. I also found that carbon levels in woodland soil aggregates vary with age, with woodlands aged between 81-160 years showing higher carbon concentrations in microaggregates and finer soil particles compared to pastures. I observed a reduction in specific root length as woodlands matured, suggesting a shift in root traits from efficient resource uptake to more conservative resource use. Fine roots play a crucial role in nutrient acquisition and symbiotic relationships with soil microorganisms, which led me to investigate the changes in microbial communities, such as bacteria and fungi, during different stages of woodland development. My research reveals that older woodlands support unique ectomycorrhizal communities influenced by tree species and woodland age. I also identified specific fungal taxa associated with different forest succession stages, providing insights into their ecological roles within woodland ecosystems. Additionally, I examine earthworm populations, which are known to play a significant role in soil bioturbation and nutrient cycling, further influencing the structure and function of the soil ecosystem. I found the abundance of earthworm functional groups vary with woodland age, with endogeic earthworms declining and epigeic earthworms increasing in relative abundance as woodlands mature. Species diversity increased with woodland age, peaking in the oldest woodlands. Woodland age and ground cover were identified as significant environmental factors influencing earthworm populations. Overall, this thesis provides a comprehensive understanding of the ecological changes that occur during woodland creation and succession, highlighting the complex relationships between soil carbon storage, root morphology, microbial communities, and earthworm populations. My findings contribute to the field of forest ecology and can inform forest management practices to enhance biodiversity and ecological health.