New paper by Ribeiro –Kumara et al. studied how fire-induced changes to soil properties and vegetation affect gas exchange of CO₂, CH₄ and N₂O in the soil–atmosphere interface of hemiboreal Scots pine forests in Estonia.

The results showed a reduction of soil CO₂ efflux at the beginning of the fire chronosequence, but no changes to CH₄ or N₂O fluxes related to time after fire. Soil respiration responded differently to changes in soil temperature and soil moisture across the fire chronosequence. Conversely, CH₄ and N₂O fluxes only responded to changes in soil temperature. Recovery of soil respiration in the long term was associated with the moderate effect of fire on enzyme activity, the above- and below-ground litter C input, and the re-establishment of overstorey vegetation. Enzyme activity and decomposition inside the litter bags were especially good indicators of the role of the microbiota on the initial recovery of soil respiration prior to the re-establishment of the vegetation

Despite its limitations, the study certainly adds to our understanding of the importance and complexity of both above- and below-ground (vegetation and microbiota) responses to fire-induced changes of soil physicochemical properties for determining the temporal variability of gas exchange.

REFORMWATER- Reducing the effects of forest management to inland waters, is a new project lead by Prof. J. Pumpanen (WaterWorks2017 ERA-NET Cofund, April 1, 2019 – March 3, 2022).

The aim of this project is to quantify the effects of current management practices (harvesting and subsequent ditch network maintenance) on peatland forests on the transport of dissolved organic matter to aquatic systems and consequent greenhouse gas emissions. Also alternative forest management techiques such as continuous cover forestry to reduce the DOM load to inland waters will be studied.

The project is based on field experiments where the effects of different forest management techniques on water quality will be tested. Detailed laboratory experiments for determining the effect of DOM quality on greenhouse gas production from aquatic systems will be performed.

The project is based on multidisciplinary collaboration between foresters, soil scientists and limnologists from Finland (University of Eastern Finland, University of Helsinki), Sweden (Swedish University of Agricultural Sciences, Umeå)), Estonia (University of Tartu) and Ireland (University College Dublin.

Fieldworks in Finland (Paroninkorpi), 21-22. October 2019

From 06. – 07. October Work Group 3 (Fire Effects on Soil) meeting „Soils and forest fires today. Science and Society“ and from 08.-09. October First General Assembly & 2nd MC meeting were taking place in Soffia, Bulgaria.

Our team members Prof. Jukka Pumpanen (University of Eastern Finland) and Dr. Kajar Köster (University of Helsinki) are members of the Management Committee (country representatives) of the new COST Action CA18135, Fire in the Earth System: Science & Society (FIRElinks).

Dr Egle Köster (University of Helsinki) and Ms Christine Ribeiro-Kumara (University of Helsinki) are acting as Management Committee Substitutes.

FIRElinks will develop the EU-spanning network of scientists and practitioners involved in forest fire research and land management with backgrounds such as fire dynamics, fire risk management, fire effects on vegetation, fauna, soil and water, and socio-economic, historical, geographical, political perception and land management approaches. It will connect communities from different scientific and geographic backgrounds, allowing the discussion of different experiences and the emergence of new approaches to fire research.

The main aim of FIRElinks is to power synergistic collaborations between European research groups and stakeholders with the objective to synthesise the existing knowledge and expertise, and to define a concerted research agenda which promotes an integrated approach to create fire-resilient landscapes, taking into account biological, biochemical and-physical, but also socio-economic, historical, geographical, sociological, perception and policy constraints. This is an urgent societal need due to expected further intensification and geographical spreading of wildfire regimes under Global Change.

New paper by Aaltonen et al., 2019 determines how heterotrophic soil respiration (Rh), originating from the decomposition of SOM, and the Q10 of this process vary between different depths over the years following a forest fire in permafrost-affected soils. How the microbial biomass and qCO2 are affected by the fire, and what are the most important factors affecting the Q10 of SOM decomposition.

The results indicate that forest fires may facilitate the decomposition of permafrost SOM by increasing the active layer depth, but on the same time fire increased the temperature sensitivity of decomposition. The SOM in the permafrost surface was less temperature sensitive than the SOM in the soil surface. The post-fire decreases in ground vegetation were reflected in the SOM temperature sensitivity shortly after fire but seemed to return to original levels with forest succession.

The fire also increased the microbial qCO2, and these changes partly explain the lack of significant decrease in heterotrophic soil respiration after fire, as the microbes may use more C for respiration in the recently burned areas compared with the older areas. Even though fires increased the active layer depth, the decrease in SOM quality caused by fire may limit the decomposition rate to some degree.

New paper by Aaltonen et al., 2019 studied how the proportions of insoluble (recalcitrant) and soluble (labile) fractions in soil organic matter (SOM) change as a result of forest fire in the active layer on permafrost, and what are the most important factors (active layer depth, soil temperature, biomass, C/N ratio) explaining the size of insoluble (recalcitrant) fractions of SOM post-fire. Also the abundancies of stable isotopes δ 15N and δ 13C change along with depth and time since last fire was studied.

The SOM fraction ratios reverted towards pre-fire status with succession. Changes in SOM were less apparent deeper in the soil. Best predictors for the size of recalcitrant SOM fraction were active layer depth, vegetation biomass and soil C/N ratio, whereas microbial biomass was best predicted by the size of the recalcitrant SOM fraction. Results indicated that SOM in upland mineral soils at the permafrost surface could be mainly recalcitrant and its decomposition not particularly sensitive to changes resulting from fire.

New paper by Peng et al 2019 dealing with effects of biochar addition on the fluxes and C turnover in boreal forests soils.

The results of the study indicate that wood-derived biochar produced at high pyrolysis temperatures had no significant effects on soil heterotrophic respiration obtained from lab incubations in boreal Scots pine forests at 5 to 10 Mg ha–1 application rates. Biochar addition increased soil total organic C, C/N ratio, and moisture content, but had no clear effect on soil total N, nor on the temperature sensitivity of soil respiration. The turnover time of soil C was unaffected by biochar addition. These results indicate that from a C sequestration point of view, biochar addition did not accelerate the mineralization of soil organic C, and could lead to higher stable C stocks in the surface soil layer.

On 11th December 2018, already fourth Finnish Biochar Seminar was held in Viikki, Helsinki.

Our team members Prof. Jukka Pumpanen and Dr. Egle Köster presented their latest results there:

Prof. Jukka Pumpanen, University of Eastern Finland  “Effects of biochar on fluxes and turnover of carbon in boreal forest soils”

Dr. Egle Köster, University of Helsinki  “Biochar as a possible new tool for reforestation practices”

Team of Disturbances and Biogeochemistry (University of Helsinki) and SNS/EFINORD network Natural Disturbance Dynamics Analysis for Forest Ecosystem Based Management (FORDISMAN) were organizing joint workshop: “Disturbance legacy and forest soil carbon” in Hyytiälä (7-9 November 2018).

Thursday (08. November) was a day full of presentations from scientists from Finland (University of Helsinki, University of Eastern Finland), Estonia (Estonian University of Life Sciences) and Latvia (Latvian State Forest Research Institute “Silava”).

ARCTICFIRE had a special session on that workshop with seven presentations covering most of the research done under that project.

Friday (09. November) was excursion day, where the participants were visiting SMEAR II station in Hyytiälä.

Currently there is also Special Issue “Natural Disturbance Dynamics Analysis for Forest Ecosystem Management” (with abstract submission deadline in 30 October 2019) under development in Journal Forests.

New paper by Zhou et al 2018 dealing with the impact of wildfire on microbial C:N:P stoichiometry and the fungal-to-bacterial ratio in permafrost soils.

The results of the study indicate that forest wildfire increased the active layer depth and subsequently decreased soil moisture and vegetation coverage. This consequently led to a decrease in the microbial C and N contents as well as the F:B ratios. However, the C:N:P ratios in the microbial biomass remained relatively constant over time following a wildfire, indicating homeostatic regulation. Wildfire also failed to affect the microbial communities in the deep soil layers.

These results indicate a complex interaction between the decomposer community, resource availability, and successional stage. Forest wildfire either shifted the microbial diversity or suppressed the microbial growth rate for several decades.