The effects of forest management on carbon dynamics of soil organic horizons

Lanfranchi, Mauro (2020) The effects of forest management on carbon dynamics of soil organic horizons. PhD thesis, Lancaster University.

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The carbon sink potential of temperate forests plays a central role in climate change mitigation strategies, and soil organic carbon sequestration can be achieved through afforestation and reforestation. Yet, the main factors responsible for influencing the dynamics of long-term forest carbon stabilization within the soil are poorly understood. This study investigates how different forest management practices affect the carbon sequestration potential within the soil organic surface horizon (Litter, Fragmented and Humic) under second rotation Picea sitchensis plantations in the UK. Fieldwork activities were carried out in two experimental sites of upland Britain to collect samples related to soil carbon quantity, carbon quality and the dynamics of fine root turnover. Two separate experiments were carried out. The first was on a pre-existing experimental site (Forest of Ae) to assess differences between conventional stem-only harvest, whole-tree harvest and fertilization. The second experiment was designed on an existing trial (Clocaenog forest) to compare a stand with no interventions in the overstory or understory since the research area was established in 2002 (Control), and one stand in transformation to continuous cover forestry (irregular shelterwood). At the Forest of Ae, results revealed that fertilization practices had a significant, positive effect on soil carbon storage within the L horizon (conventional harvest p < 0.01, whole-tree harvest p < 0.01). Brash retained on site at the time of harvesting had a significant, positive effect on soil carbon storage within the F horizon (conventional harvesting p = 0.03 and fertilization p = 0.01). Results also suggest that soil nitrogen concentration can be used to predict the soil carbon storage of each organic horizon (adjR2= 0.931). Also, the fine root necromass within the 15 to 30 cm soil depth is significantly higher (p = 0.02) in the fertilized treatment when compared with whole-tree harvest, although this does not affect the carbon storage within the H horizon. At Clocaenog forest, transformation to irregular shelterwood had a highly significant, positive effect on soil carbon storage within the soil H horizon (p < 0.01). Soil nitrogen concentration, C:N ratios and available nitrogen all consistently point towards a higher presence of nitrogen in the Control treatment which could be responsible for SOC and N mineralization in the H horizon. Overall, the study shows that forest management decisions do affect C storage in the organic soil horizons of commercial forest plantations in upland Britain. These dynamics need to be taken into account in C and GHG balances and guidelines for soil protection.

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08 Feb 2021 15:25
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05 Jun 2024 23:44