New frontiers in forest carbon processes: soil chars, methane emission hotspots, and high-resolution inventory

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Forests play a central role in global greenhouse gas dynamics, constituting a critical but environmentally sensitive sink for both carbon dioxide and methane. The present proposal addresses emerging research problems that link tree biology to forest carbon processes, with a focus on two important and inter-related components of the forest carbon cycle that are poorly resolved: soil charcoals (both natural chars and designed "biochars") and effects of trees on soil fluxes of CO2 and methane, with particular attention to "methane emission hotspots". Natural chars occur in most forest soils, and are increasingly recognized as playing a critical role in soil nutrient and carbon dynamics that has been drastically modified by fire suppression. The physico-chemical properties and dynamics of chars remain poorly characterized, but likely vary greatly with source tree species, fire intensity, and char weathering; the comparability of natural chars to designed "biochars" has received almost no attention. The proposed studies will: (1) quantify spatial variability in natural chars in temperate, boreal, and tropical forest ecosystems, testing the hypothesis that char quantities are predictable from site topography and hydrology and influence both productivity and community composition; (2) quantify and experimentally elucidate mechanisms for species-specific tree responses to char; (3) examine long-term effects of char additions to forest productivity, ecosystem processes, and biodiversity. Methane flux is similarly critical in understanding forest-climate feedbacks, but the drivers of methane dynamics in forest ecosystems remain poorly understood. Instrumentation has only recently become available to enable rapid, accurate field measurements of methane flux. The proposed studies will: (1) quantify spatial variability in soil methane and CO2 efflux in relation to soil variables and local tree community composition; (2) test for effects of tree size and species on soil methane and CO2 efflux; (3) assess methane emissions from coarse woody debris and live tree heartrot; (4) examine soil methane and CO2 efflux rates in relation to soil chars, testing the hypothesis that chars will increase soil oxygenation (and thus increase net methane uptake) due to increased porosity. Together the proposed studies will provide fundamental science needed to better manage forests for climate mitigation, specifically focusing on novel approaches involving designed biochars and enhancements for forest methane sinks.