Recovery of carbon stocks after wildfires in boreal forests : a synthesis

Book of abstracts Cool forests at risk? The Critical Role of Boreal and Mountain Ecosystems for People, Bioeconomy, and ClimatePeer reviewe

Fire-induced changes of high and low intensity prescribed fires in a Canadian boreal forest

Geophysical Research AbstractsVol. 21, EGU2019-7859, 2019EGU General Assembly 2019The degree of fire-induced effects on boreal forest soils substantially depends on the intensityof fire. Especially high-intensity fires may drastically alter the quality and quantity of the soilorganic matter pool. In this study, we investigated the effects of low and high intensityprescribed fires on soil carbon and nitrogen contents, soil pH, soil temperature, and soilmoisture in a Canadian boreal forest. The study was based on intensive field sampling duringAugust 2018 in Jack pine (Pinus banksiana) forest stands located 50 km north of FortProvidence, Northwest Territories (61.582˚ ; -117.165˚). We measured the soil parametersfrom two short-term fire chronosequences — one with high-intensity prescribed fireshappening in years 2000, 2012, 2015, 2016, and 2017; and the other with low-intensityprescribed fires happening in years 2015, 2017, and 2018. Additionally, we measured soiltemperature and moisture before and after a low-intensity prescribed fire. In thehigh-intensity fire chronosequence, the study site burned in year 2012 had the lowest soiltemperature. Even though temperatures seemed slightly higher in the most recent years ofthe fire chronosequence (2015, 2016, and 2017), we did not identify a clear trend.Soil moisture was the lowest in the study site burned in year 2000, with mostly nosignificant differences between the following years. We did not find significantdifferences in soil moisture and soil temperature before and after a low-intensityprescribed fire. However, both time-after-fire and fire intensity were important forsoil moisture prediction, whereas only fire intensity was important for predictingsoil temperature. Soil pH in the humus layer of the study site burned in 2012 wassignificantly lower compared to the other age classes (no pH data for year 2000) of thehigh-intensity fire chronosequence. Neither C nor N content were significantly differentbetween the fire age classes at the humus layer or at the mineral layers. We believethat the small sample size did not allow the identification of further differencesbetween the age classes, and it prevented direct comparisons between high and lowintensity fires. Despite its exploratory nature, this study offers some insight intoshort-term effects of fire on some soil parameters, for example, the observed changeson soil moisture, soil temperature, and soil pH. Therefore, we will progress thiswork by increasing the sample size and analysing autotrophic and heterotrophic soilrespiration to directly infer on fire-induced changes on the soil organic matter pool.Non peer reviewe

Biochar as a possible solution to shortcomings of traditional forest biomass utilization in Finland

Proceeding volume: 19Non peer reviewe

High carbon losses from established growing sites delay the carbon sequestration benefits of street tree plantings - A case study in Helsinki, Finland

We assessed the net carbon (C) sequestration dynamics of street tree plantings based on 10 years of measurements at two case study sites each with different tree species in Helsinki, Finland. We assessed C loss from tree soils and tree C accumulation, tested the applicability of pre-existing growth and biomass equations against observations, and estimated the time point for the beginning of net C sequestration for the studied street tree plantings. The tree woody biomass C accumulation in the first 10 years after planting was 18-32 kg per tree. At the same time the C loss from the growth media was at least 170 kg per growth media volume (25 m(3)) per tree. If this soil C loss was accounted for, the net C sequestration would begin, at best, approximately 30 years after planting. Biomass equations developed for traditional forests predicted more stem biomass and less leaf and branch biomass than measured for the species examined, but total aboveground biomass was generally well predicted.Peer reviewe

Soil organic matter decomposition and temperature sensitivity after forest fire in permafrost regions in Canada

Non peer reviewe

Grazing by reindeer in subarctic coniferous forests – how it is affecting three main greenhouse gas emissions from soils

Non peer reviewe

Microbial biodiversity contributes to soil carbon release : a case study on fire disturbed boreal forests

Microbial biodiversity plays the dominant role in soil carbon emissions in fire-disturbed boreal forests. Microbial communities often possess enormous diversity, raising questions about whether this diversity drives ecosystem functioning, especially the influence of diversity on soil decomposition and respiration. Although functional redundancy is widely observed in soil microorganisms, evidence that species occupy distinct metabolic niches has also emerged. In this paper, we found that apart from the environmental variables, increases in microbial diversity, notably bacterial diversity, lead to an increase in soil C emissions. This was demonstrated using structural equation modelling (SEM), linking soil respiration with naturally differing levels of soil physio-chemical properties, vegetation coverage, and microbial diversity after fire disturbance. Our SEMs also revealed that models including bacterial diversity explained more variation of soil CO2 emissions (about 45%) than fungal diversity (about 38%). A possible explanation of this discrepancy is that fungi are more multifunctional than bacteria and, therefore, an increase in fungal diversity does not necessarily change soil respiration. Further analysis on functional gene structure suggested that bacterial and fungal diversities mainly explain the potential decomposition of recalcitrant C compare with that of labile C. Overall, by incorporating microbial diversity and the environmental variables, the predictive power of models on soil C emission was significantly improved, indicating microbial diversity is crucial for predicting ecosystem functions.Peer reviewe

Contrasting effects of reindeer grazing on CO2, CH4, and N2O fluxes originating from the northern boreal forest floor

SPECIAL ISSUE ARTICLE Editor Dr. Chris J. BarrowReindeer (Rangifer tarandus L.) is considered to be an important mammalian herbivore, strongly influencing Arctic lichen-dominated ecosystems. There is no wide knowledge about the effect of reindeer on greenhouse gas (GHG) fluxes in northern boreal forests. Ground vegetation plays an important role in absorbing nitrogen (N) and carbon dioxide (CO2) from the atmosphere. Lately, it has also been found to be a significant source of nitrous oxide (N2O) and a small source of methane (CH4). We investigated the influence of reindeer grazing on field layer GHG (CO2, CH4, and N2O) fluxes, ground vegetation coverage and biomass, and soil physical properties (temperature and moisture) in a northern boreal forest. At our study site, the reindeer-induced replacement of lichen by mosses had contrasting effects on the GHG fluxes originating from the field layer. Field layer CO2 efflux was significantly higher in grazed areas. The field layer was a CH4 sink in all areas, but grazed areas absorbed more CH4 compared to non-grazed areas. Although total N2O fluxes remained around 0 in grazed areas, a small N2O sink occurred in non-grazed areas with lower moss biomass. Our results indicated that grazing by reindeer in northern boreal forests affects GHG fluxes from the forest field layer both positively and negatively, and these emissions largely depend on grazing-induced changes in vegetation composition.Peer reviewe

Purification of Forest Clear-Cut Runoff Water Using Biochar: A Meso-Scale Laboratory Column Experiment

Biochar can be an effective sorbent material for removal of nutrients from water due to its high specific surface area, porous structure, and high cation and anion exchange capacity. The aim of this study was to test a biochar reactor and to evaluate its efficiency in runoff water purification and consecutive nutrient recycling in clear-cut peatland forests. The goodness of the method was tested in a meso-scale (water volume thousands of liters) reactor experiment by circulating runoff water through wood biochar-filled columns and by determining water nutrient concentrations in the column inlet and outlet. The pseudo-first and second order kinetic models were fitted to the experimental data and the adsorption rate (Kad) and maximum adsorption capacity (Qmax) of the biochar reactor were quantified. The concentration of total nitrogen (TN) decreased by 58% during the 8-week experiment; the majority of TN adsorption occurred within the first 3 days. In addition, NO3-N and NH4-N concentrations decreased below the detection limit in 5 days after the beginning of the experiment. The maximum adsorption capacity of the biochar reactor varied between 0.03–0.04 mg g−1 biochar for NH4-N, and was equal to 0.02 mg g−1 biochar for TN. The results demonstrated that the biochar reactor was not able to adsorb TN when the water TN concentration was below 0.4 mg L−1. These results suggest that a biochar reactor can be a useful and effective method for runoff water purification in clear-cut forests and further development and testing is warranted. Unlike traditional water protection methods in peatland forestry, the biochar reactor can effectively remove NO3-N from water. This makes the biochar reactor a promising water protection tool to be tested in sites where there is the risk of a high rate of nutrient export after forest harvesting or drainage