New frontiers in forest carbon processes: novel methane dynamics, pyrogenic carbon, and restoration of highly impacted sites

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Forests play a central role in the global carbon cycle. Methane (CH4) accounts for >25% of anthropogenic climate forcing, with forests acting as both important CH4 sources and sinks. Recent studies suggest important fluxes through tree stems and foliar tissues, and our lab has discovered "hotspots" of CH4 efflux in highly impacted soils in managed forests. Recent studies also indicate pervasive but patchy fire-legacy pyrogenic carbon (PyC) in forest soils that can greatly increase tree growth and possibly enhance soil CH4 oxidation. There is currently insufficient knowledge on either patterns or mechanisms involved to integrate these processes into global models or to inform forest management. We propose three inter-related projects to address these research gaps. (1) RELATIONS BETWEEN PYC, FOREST COMPOSITION, AND SOIL GHG FLUX. PyC from fire residues or added to soils as biochar can potentially strongly enhance tree growth by increasing soil nutrient and water retention, and reduce CH4 emissions due to enhanced soil aeration. Soil CH4 oxidation may also be reduced beneath conifers due to inhibitory effects of monoterpenes leached from litter; effects of local tree diversity on soil GHG fluxes have been proposed but not examined in forests. This project will use measurements in a large, mapped forest stand, in conjunction with long-term biochar addition and stand conversion experiments, to address these potential effects, testing the hypotheses of that increased PyC, angiosperm abundance, and local tree diversity will increase local soil CH4 oxidation. (2) MITIGATION OF CH4 EMISSION HOTSPOTS IN MANAGED FOREST AND URBAN GREEN INFRASTRUCTURE. Our recent studies show that highly degraded soils at log landings in temperate forests are "hotspots" of high soil CH4 efflux. This project will use observational studies and experiments to assess whether this pattern also is found in managed boreal forests and urban green infrastructure, to better understand the mechanisms involved, and to test mitigation approaches involving biochar additions, soil inoculations, and other soil treatments. (3) NOVEL METHANE DYNAMICS: CH4 OXIDATION BY CANOPY FOLIAGE. Our preliminary measurements indicate that tree foliage on upland (well-drained) sites is an important CH4 sink; however, little is known concerning either mechanisms or patterns of variation among species or among forest types. Survey studies will test the hypothesis that foliar CH4 uptake capacity is correlated with "leaf economics" traits, that seasonal leaf colonization by methanotrophs results in predictable seasonal patterns and canopy stratification of CH4 uptake, and that foliar CH4 uptake is reduced in urban settings due to a lack of methanotroph colonization. The proposed research programme will contribute to fundamental understanding of CH4 dynamics and C processes in forests, and will also directly develop novel approaches to climate mitigation applicable in forestry and urban green infrastructure.