Prescribed burning of logging slash in the boreal forest of Finland: emissions and effects on meteorological quantities and soil properties

摘要

A prescribed fire experiment was conducted on 26 June 2009 inHyytiälä, Finland, to study aerosol and trace gas emissions fromprescribed fires of slash fuels and the effects of fire on soil properties ina controlled environment. A 0.8 ha forest near the SMEAR II measurement station (Station forMeasuring Ecosystem-Atmosphere Relations) was cut clear; some treetrunks, all tree tops and branches were left on the ground andburned. The amount of burned organic material was ~46.8 tons (i.e.,~60 tons ha). The flaming phase lasted 2 h 15 min, thesmoldering phase 3 h. Measurements were conducted on the ground with bothfixed and mobile instrumentation, and in the air from a research aircraft. Inthe middle of the burning area, CO concentration peaked around2000–3000 ppm above the baseline, and peak vertical flow velocities were~9 m s, as measured with a 10 Hz 3-D sonic anemometer placedwithin the burn area. In the mobile measurements the peak particle numberconcentrations were approximately 1–2 × 10 cm in theplume at a distance of 100–200 m from the burn area. On the ground at theSMEAR II station the geometric mean diameter of the mode with the highestconcentration was 80 ± 1 nm during the flaming phase and in themiddle of the smoldering phase, but, at the end of the smoldering phase,the largest mode was 122 nm. In the volume size distributions, geometricmean diameter of the largest volume mode was 153 nm during the flaming phaseand 300 nm during the smoldering phase. The lowest single-scattering albedoof the ground-level measurements was 0.7 in the flaming-phase plume and~0.9 in the smoldering phase. Elevated concentrations of several volatileorganic compounds (VOC) (including acetonitrile, a biomass burningmarker) were observed in the smoke plume at ground level.Measurements at the forest floor (i.e., a richly organiclayer of soil and debris, characteristic of forested land) showed that VOCfluxes were generally low and consisted mainly of monoterpenes, and VOC fluxpeaked after the burning. After one year, the fluxes had nearly stabilizedclose to the level before the burning. The clear-cutting and burning of slashincreased the total long-term CO release from the soil, and altered thephysical, chemical and biological properties of the soil, such as increasedthe available nitrogen contents of the soil, which in turn, affected thelong-term fluxes of greenhouse gases.