Tue, Aug 16, 2022: 2:00 PM-2:15 PM
512E
Background/Question/MethodsAlthough forests are globally important both as sources and sinks for CH4, recommendations for “climate-smart” forest management have not considered forest CH4 dynamics, and relevant data remains sparse. We have recently completed a series of studies on CH4 flux and its components in continuous-cover managed forest in Ontario, making use of a portable gas analysis system that allows accurate real-time estimates of fluxes as low as 0.02 nmol m-2 s-1. Quantification of CH4 fluxes from tree stems, branches, foliage, tree wounds, and coarse woody debris, and of harvest-related soil disturbance on soil CH4 fluxes allows estimates of the whole-forest CH4 budget under alternative management regimes.
Results/ConclusionsIn upland sites, tree foliage consistently showed CH4 uptake, though roughly balanced by CH4 emissions from branches. Branch and foliage fluxes were ~10-fold the CH4 emission from main stems. Coarse woody debris acted as weak CH4 sink and tree wounds as a source comparable to main stems. Soil disturbance from logging machinery resulted in conversion of heavily trafficked sites from CH4 sinks to CH4 sources; the most heavily impacted sites showed emissions greater than regional wetlands, with peak emissions in areas where fine wood particles are incorporated into soil. Heavily impacted soils did not recover a CH4 sink comparable to unimpacted soils within 20 years, which is the prevailing felling cycle length. The issue of “logging scars” in forest carbon budgets has been a recent focus of the Canadian eNGO community: our results suggest that reductions in CH4 sinks or conversion of forests from CH4 sinks to sources are pervasive. Management practices that could enhance net forest CH4 uptake include soil protection, enhanced skid trail planning, and targeted restoration of CH4 emission “hotspots” such as log landings. Preliminary estimates suggest that “methane-smart” forest management could be of similar importance globally to CH4 emissions mitigation in the agricultural sector.
Results/ConclusionsIn upland sites, tree foliage consistently showed CH4 uptake, though roughly balanced by CH4 emissions from branches. Branch and foliage fluxes were ~10-fold the CH4 emission from main stems. Coarse woody debris acted as weak CH4 sink and tree wounds as a source comparable to main stems. Soil disturbance from logging machinery resulted in conversion of heavily trafficked sites from CH4 sinks to CH4 sources; the most heavily impacted sites showed emissions greater than regional wetlands, with peak emissions in areas where fine wood particles are incorporated into soil. Heavily impacted soils did not recover a CH4 sink comparable to unimpacted soils within 20 years, which is the prevailing felling cycle length. The issue of “logging scars” in forest carbon budgets has been a recent focus of the Canadian eNGO community: our results suggest that reductions in CH4 sinks or conversion of forests from CH4 sinks to sources are pervasive. Management practices that could enhance net forest CH4 uptake include soil protection, enhanced skid trail planning, and targeted restoration of CH4 emission “hotspots” such as log landings. Preliminary estimates suggest that “methane-smart” forest management could be of similar importance globally to CH4 emissions mitigation in the agricultural sector.