Log landings are methane emission hotspots in managed forests

Abstract

Log landings are areas within managed forests used to process and store felled trees prior to transport. Through their construction and use soil is removed or redistributed, compacted, and organic matter contents may be increased by incorporation of wood fragments. The effects of these changes to soil properties on methane (CH4) flux are unclear and unstudied. We quantified CH4 flux rates from year-old landings in Ontario, Canada, and examined spatial variability and relationships to soil properties within these sites. Landings emitted CH4 throughout the growing season; the average CH4 emission rate from log landings was 69.2 ± 12.8 nmol·m−2·s−1 (26.2 ± 4.8 g CH4-C·m−2·year−1), a rate comparable to CH4-emitting wetlands. Emission rates were correlated to soil pH, organic matter content, and quantities of buried woody debris. These properties led to strong CH4 emissions, or “hotspots”, in certain areas of landings, particularly where processing of logs occurred and incorporated woody debris into the soil. At the forest level, emissions from landings were estimated to offset ∼12% of CH4 consumption from soils within the harvest area, although making up only ∼0.5% of the harvest area. Management practices to avoid or remediate these emissions should be developed as a priority measure in “climate-smart” forestry.