Changes in biogeochemistry and carbon fluxes in a boreal forest after the clear-cutting and partial burning of slash

Abstract

We quantified the changes in the soil properties and fluxes of soil CO2, CH4 and volatile organic compound (VOC) fluxes following a clear-cut (CC) and prescribed burning of slash (BCC) over a three year time period in a mature spruce forest. Clear-cutting increased soil moisture, soil temperature, pH as well as NH4–N and NO3–N concentrations in the soil. PH and soil temperature in the BCC site were even higher than in the CC site.Probably due to decreased tree root respiration, the soil CO2 efflux decreased only slightly in the first growing season following the clear-cut. During the following two years, the CO2 efflux at the CC site was significantly higher than in the mature control forest due to increased decomposition, which was stimulated by higher soil moisture and temperature. The temperature dependencies of the CO2 efflux did not differ between these sites. The clear-cut and burning of slash, however, decreased the CO2 efflux and its temperature response in BCC for two years but in the third year, the differences between control and BCC were no longer significant.Soil was a sink for CH4 in all treatments. After the clear-cutting and burning of slash, the net CH4 uptake was immediately decreased, but one year later the uptake was comparable to that of the mature control forest. The CC treatment decreased the soil CH4 uptake, however, it did not significantly differ from that of the control.The soil VOC emissions measured at the BCC site were 100-fold compared to those measured before clear-cutting, but the emissions decreased rapidly during the three months following the burning.Although the CO2 effluxes from the BCC site were lower for more than 2.5 years compared to the CC site, the total amount of carbon released from prescribed burning was higher due to the immediate carbon losses. Moreover, the clear-cut and burning of slash temporarily decreased the ability of the forest to bind atmospheric CH4 and increased the VOC emissions significantly.