Boreal forest soil carbon fluxes one year after a wildfire: Effects of burn severity and management

The extreme 2018 hot drought that affected central and northern Europe led to the worst wildfire season in Sweden in over a century. The Ljusdal fire complex, the largest area burnt that year (8995 ha), offered a rare opportunity to quantify the combined impacts of wildfire and post-fire management on Scandinavian boreal forests. We present chamber measurements of soil CO2 and CH4 fluxes, soil microclimate and nutrient content from five Pinus sylvestris sites for the first growing season after the fire. We analysed the effects of three factors on forest soils: burn severity, salvage-logging and stand age. None of these caused significant differences in soil CH4 uptake. Soil respiration, however, declined significantly after a high-severity fire (complete tree mortality) but not after a low-severity fire (no tree mortality), despite substantial losses of the organic layer. Tree root respiration is thus key in determining post-fire soil CO2 emissions and may benefit, along with heterotrophic respiration, from the nutrient pulse after a low-severity fire. Salvage-logging after a high-severity fire had no significant effects on soil carbon fluxes, microclimate or nutrient content compared with leaving the dead trees standing, although differences are expected to emerge in the long term. In contrast, the impact of stand age was substantial: a young burnt stand experienced more extreme microclimate, lower soil nutrient supply and significantly lower soil respiration than a mature burnt stand, due to a thinner organic layer and the decade-long effects of a previous clear-cut and soil scarification. Disturbance history and burn severity are, therefore, important factors for predicting changes in the boreal forest carbon sink after wildfires. The presented short-term effects and ongoing monitoring will provide essential information for sustainable management strategies in response to the increasing risk of wildfire

Phytomass of litter fall in postfire larch forests of Zeisky nature reserve (Upper Priamurie)

Forest litter is one of the major carbon flow and main source for long-term carbon accumulation in forest ecosystems. Wild fires is a frequent and powerful event destroys fluxes of matter and carbon accumulation. In the article the first data of stationary investigation of litter fall in flow and its organic matter content in larch forest (Larix gmelinii (Rupr.) Rupr.) are presented. The study is conducted on Tukuringra range in Upper Priamurie (Amur Oblast, Russia) in the forest stand recovering after fire of 2003 year. Results shows that net annual inflow of forest above ground litter fall from all vegetation in burned forest is 2.8 times lower than in background forest. Grass litter fall and other tree debris (bark, seeds, cones, etc.) are main sources for annual litter fall input in burned forest. Litter fall composition in the burned forest is significantly changed and high variation of mass of litter fall fractions is observed. Accumulation of carbon and nitrogen is higher in majority of litter fall fractions in burned forest as compared to control one. Annual carbon input from litter fall is 164 gm–2 in control forest and 76 gm–2 in burned forest, total amount of nitrogen derived by litter fall is 1.7 and 2.4 gm–2 for control and burned forest respectively. Our findings suggest that carbon accumulation processes in fire-prone boreal forests changed significantly. The research results can be used for modeling of carbon balance in taiga forest damaged by fire

Litter decomposition in the post-fire larch forests of the Tukuringra Range (Upper Priamurie)

Boreal forests are one of the main carbon (С) pools on the planet. Decomposition of the litter is a main mechanism of C accumulation in soil. This process is often influenced by fires. Thus, we need to enhance our understanding about decomposition of the litter in post-fire forests to better understand the mechanism of C accumulation in boreal forests. Here, we studied initial stages of decomposition of litter in the post-fire forest (12 years after fires) and in the background larch forest located in the Tukuringra mountain range in the northern part of the Amur oblast. We present the results of a field experiment on the decomposition of the main typical fractions of larch forest. We used the litter bags method for studying rate of decomposition litter (leaves, grass, branches and needles). After 150 days mass loss of litter was 36.7 % of initial mass in the post-fire forest and 39.9 % in the background forest. Mass loss was most rapid in the first 75 days of the experiment in the both cases. In both plots the rate of decomposition of litter was decreased in order: grass – leaves – needles – branches. In both the post-fire and background forests, rate of litter decomposition is a function of moisture. Soil acidity was higher in post-fire forest than background forest (5.3 and 4.8, respectively, p < 0.01). However, this soil property does not influence early stages of litter decomposition in either case