Jogeir N. Stokland
Research Professor
Abstract
Deadwood represents a dynamic carbon pool in forest ecosystems where microbial decomposition causes fluxes of CO2 to the atmosphere through respiration and organic carbon to the soil through leakage and fragmentation. This study characterises different stages of deadwood of Norway spruce (Picea abies). 35 Norway spruce trees were sampled and categorized on a 0–5 decay scale. For the 14 trees in classes 0–3, two stem discs were collected from two heights. For the 21 trees in classes 4 and 5, a single sample per tree was taken, because decay was relatively uniform throughout the stem. The relative amount of hemicellulose and cellulose declined moderately from decay class 1 to 3 and substantially from decay class 3 to class 4 but small amounts were still present in decay class 5. The relative lignin proportion increased substantially from decay class 3 to 4 and dominated in decay class 5. Relative carbon content increased from 50 to 56% during the decomposition process due to the increasing accumulation of lignin residuals being a typical signature of brown rot decay. A laboratory experiment including three species of brown rot fungi verified decomposition close to 70% of Norway spruce biomass and resulted in 55% carbon content. This was similar to the carbon content in decay class 4 and 5. A novel approach is presented to quantify the carbon flux from deadwood to the soil. First, we calculated the residual proportion of carbon in decayed wood compared to the initial carbon content of live trees. Subsequently, we extended the calculation to determine the amount of remaining carbon from non-decayed wood that was transferred to the soil during each decay class. The approach showed that Norway spruce wood decomposition under field conditions transfers at least 39–47% of the initial wood carbon to the soil carbon pool, depending on soil type. This strengthens the previously under-communicated fact that the carbon flux from deadwood to soil is higher from brown rot decomposition in boreal forests than the corresponding carbon flux in temperate and tropical forests where deadwood is more influenced by white rot fungi.
Authors
Kjersti Holt Hanssen Viktor J. Bruckman Michael Gundale Aigars Indriksons Morten Ingerslev Marju Kaivapalu Dagnija Lazdina Kristaps Makovskis Adam O’Toole Katri Ots Marjo Palviainen Jogeir N. Stokland Iveta Varnagiryte-KabasinskieneAbstract
This report summarizes the status of biochar in forestry in the Nordic-Baltic countries today. Biochar is charred material formed by pyrolysis of organic materials. In addition to improving soil physical and chemical properties and plant growth, biochar is a promising negative emission technology for storing carbon (C) in soils. The report gives an overview of current and potential uses, production methods and facilities, legislation, current and future research as well as biochar properties and effects. Forests are both a source of feedstock for biochar production and a potential beneficiary for biochar use. Production is still limited in the Nordic-Baltic countries, but commercial production is on the rise and several enterprises are in the planning or start-up phase. In this report different biochar production technologies are described. As the (modern) use of biochar for agricultural and especially forestry purposes is relatively new, in many countries there are no specific legislation regulating its use. Sometimes the use of biochar is regulated through more general laws and regulations on e.g. fertilizers or soil amendment. However, both inside and outside EU several documents and standards exist, listing recommended physical and chemical limit values for biochar. So far, most biochar studies have been conducted on agricultural soils, though research in the forestry sector is starting to emerge. The first biochar field experiments in boreal forests support that wood biochar promotes tree growth. Also, studies on the use of biochar as an additive to the growing medium in tree nurseries show promising results. Because biochar C content is high, it is recalcitrant to decomposition, and application rates to soil can be high, biochar is a promising tool to enhance the C sequestration in boreal forests. However, available biomass and production costs may be barriers for the climate change mitigation potential of biochar. When it comes to effects on biodiversity, few field-based studies have been carried out. Some studies from the Nordic region show that biochar addition may affect microbial soil communities and vegetation, at least on a short time scale. There is clearly a need for more research on the effects of biochar in forestry in the Nordic-Baltic region. Long-term effects of biochar on e.g., forest growth, biodiversity, soil carbon and climate change mitigation potential should be studied in existing and new field experiments.
Abstract
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