NWT RESEARCH DATABASE

Tags: physical sciences, permafrost, climate change, soil chemistry, forest fire, carbon, biogeochemistry, nitrogen

Objective(s): To study the long term effects of natural forest fires on the decomposition of soil organic matter in the northern Arctic and subarctic forests.

Project Description: The aim of the ARCTICFIRE project is to study the long term effects of natural forest fires on the decomposition of soil organic matter in the northern arctic and subarctic forests. The research team will study the changes in size and quality of soil carbon and nitrogen pools and fluxes after forest fires and their underlying processes in the arctic and subarctic zone, especially the interactions of permafrost and post fire carbon balances. The research team aim to test the generality of these processes around the circumpolar north including the Yukon region by comparing data from the team’s global study area to more intensely studied sites in Värriö sub-arctic research station in Finland. The outcome of the project would increase knowledge on: a) how the amount and quality of carbon and nitrogen in soil organic matter change as a result of forest fires, b) how the microbial and biochemical processes of carbon and nitrogen accumulation are affected by fire and c) how the fires affect the melting of permafrost and what are their consequences on greenhouse gas emissions (CO2, CH4 and N2O) from the soils to the atmosphere. The study will be based on chronosequence technique where forest stands with similar soil type but different fire history will be used for studying the biogeochemical changes following the fire. We will select forest stands with 5 different age classes 1-150 years since the last fire and un-burned control forests from areas having similar soil texture, altitude, precipitation and soil chemical properties such as parent material, humus type etc. The research team will select at least 5 replicate forest stands for each age class. The fire chronosequences will be established in Yukon and Northwest territories along the Dempster highway, at approximately 0-10 km distance from the highway. The research will be conducted based on intensive field sampling at the fire chronosequence sites to study soil carbon and nitrogen stocks, soil greenhouse gas fluxes, soil permafrost depth, soil temperature and water content, soil chemical and microbiological properties, vegetation changes, albedo, tree biomass and leaf area changes. The research goals will be met through the following field activities: 1. Tree Density and Age Structure Surveys will be conducted to measure tree density and age in forest stands of different ages since the last forest fire to estimate recent patterns of forest recruitment. a. Measurement of tree density: Non-destructive mapping of all trees, with data on tree size and height. Environmental impacts of this activity are minimal. b. Measurement of tree age: This activity requires taking stem cores (large trees) or stem sections (small trees) from a subset of the trees measured along the fire chronosequence. Tree cores are expected to have little effect on tree growth and survival. Stem sections require cutting down a tree or small seedling. Tree ages are then determined from counting and cross-dating annual rings in the laboratory. Sectioning of small trees is necessary to obtain accurate tree ages. 2. Soil sampling and soil measurements a. The research team will collect soil samples manually from each 25 forest stand (5 x 5 = 25) by soil corer from the surface of the soil to the bedrock. Alternatively, if the soil sampling with the corer will not work, the team will excavate 3 soil pits (1 m x 1 m in surface area) and approximately 1 m deep in each forest stand for taking soil samples from each soil layer. The samples will be stored frozen and pre-treated in the laboratory at the University of Alberta in Edmonton for shipping to Finland for further analysis. After the sampling, the soil pits will be filled with the soil excavated from the pits to avoid leaving permanent marks on the sampling sites. b. For measuring soil greenhouse gas fluxes, the research team will carry out chamber measurements with portable chambers with CO2 analyser enclosed into the chamber. The team will also take air samples from the chambers and analyse them later in Finland with a gas chromatograph. c. The research team will also measure the soil temperature profile and soil water content during the sampling campaign from the sample plots established in the forest stands. 3. Environmental Measurements. The microenvironment of each experimental site will be characterized by measuring active layer depth, bulk density of the soil organic layers, mineral soil texture, pH, and soil temperature during the field measurement campaign at the sites. Temperature sensors will be positioned to 1-3 soil profiles at each measurement site for the field campaign to characterize the soil temperature profile in the late summer. Probes were positioned at 10, 20, 30, 40 cm and 50 cm depths down to the surface of the permafrost layer. The sensors will remain in place until the end of the field portion of this research project. The research team will send the reprints of the scientific reports to the Aurora Research Institute. The team will write a summary of the research results in plain English written for local interested people and distributed in electronic form to local communities. The fieldwork for this study will be conducted from July 2, 2015 to August 3, 2015.