Carbon sequestration in Norwegian spruce forest soils

Norway has pledged to reduce its greenhouse gas emissions, and one of the strategies and ultimate goal is to increase the short and long-term sequestration of organic carbon in forest soil to enhance this major carbon stock. Generally, soil carbon makes up a large part of the carbon pool in boreal forests, and any disturbance-induced losses could be directly linked to the size of this pool. The decomposition of soil carbon is strongly influenced by temperature and moisture, both of which are impacted by climate change. Altering forest management strategies, such as extending rotation periods and clear-cutting methods, may either increase soil carbon storage or limit its loss. In this new project we will examine soil carbon stock changes over an approximately twelve-year period in nine stands that represent three typical management stages of Norwegian spruce forests: recently clear-cut stands, mature planted production forests, and older, naturally-established stands with no active management. We aim to identify the key drivers for soil carbon storage and stability, such as biological stability and temperature sensitivity, and factors affecting chemical and physical stability. We will quantify the standing tree biomass, the source of soil carbon from above and below ground tree litter and dead wood, the age of the soil carbon as well as the microbial diversity and abundance in these forest systems. The project aims to identify links between soil carbon changes, ecosystem carbon stocks, processes, microbial community structure, and diversity. Findings will be integrated with data from previous research projects to evaluate larger scale patterns in forest carbon stocks and dynamics. Furthermore, the project seeks to facilitate knowledge transfers between researchers, the forest industry, and stakeholders, and support the development of strategies for increased soil carbon sequestration in relation to management and climate change.

The goal of augmenting short- and long-term storage of soil organic carbon (SOC) aligns with Norway’s commitment to curb climate gas emissions by 40% before 2030. Forest management strategies, such as prolonged rotation periods and clear-cutting, could potentially enhance SOC storage or contribute to its loss. A major part of the carbon pool in boreal forests is stored in the soil, and the magnitude of disturbance-induced losses of SOC may be closely related to the size of the SOC pool. Further, decomposition of SOC is primarily influenced by temperature and moisture, two factors that are significantly affected by climate change. In the current project we will quantify SOC stock changes over a 12-year period in nine stands that represent three typical Norwegian spruce forest management stages: i) recent clear-cut stands, ii) mature planted production forest, and iii) older stands established naturally prior to 1940 with no active management (near-natural stands). We will quantify changes in SOC (WP2) and its relationship with stand characteristics (WP1), C stocks in living trees, understory vegetation (WP3) and dead wood (WP4). We will identify principal drivers for SOC storage and stability which includes assessments of biological stability and its temperature sensitivity, factors affecting chemical and physical stability such as lignin, tannins, POM, MAOM, determine the source and age of SOC (13C, 14C) (WP2), as well as assess the microbial diversity and abundance and fungal biomass (WP5). Additionally, input-output fluxes of litter and CO2, tree growth patterns, natural mortality, and dead-wood decay will be quantified at selected locations. The new findings will be combined with data on forest carbon stocks and processes sourced from previous projects to discern similarities and differences and evaluate patterns in stocks and processes at a larger scale in order to identify forest management practices that facilitate C accumulation in Norwegian forest soils.