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Sea level rise and intensifying storms cause salinization and freshwater inundation of coastal forest soils which can result in tree mortality and altered ecosystem carbon (C) cycling. However, it is not yet clear if increased salinity and inundation will affect greenhouse gas (GHG) emissions to feed back with climate change. To assess the impacts of in situ chronic and pulsed salinity on GHG fluxes from coastal forests, we made continuous measurements of carbon dioxide and methane fluxes from intact soil cores collected in 1) an upland forest dominated by loblolly pine (Pinus taeda) and a freshwater swamp dominated by baldcypress (Taxodium distichum) 2) adjacent forest stands within forest types experiencing high versus low salinization and associated tree mortality and 3) before and after pulsed salinity from a hurricane related storm surge. In lab mesocosms, all soil cores were exposed to three levels of rainwater addition to assess potential interactive effects between salinization and inundation. We found that chronic salinization and associated tree mortality decreased soil CO2 fluxes in loblolly, but not baldcypress forest with in situ soil inundation patterns potentially driving the site effect. Additionally, in an upland loblolly forest, pulsed salinity from a storm surge exhibited the potential to increase CH4 fluxes. Finally, the effect of rainwater inundation on CH4 fluxes was greater in low compared to high salinity stands suggesting that salinization may have suppressed the effects of rainwater inundation on CH4 fluxes. Overall, we show that complex interactions between biotic and abiotic conditions in stressed coastal forests can alter GHG emissions, highlighting a need for future research focused on understanding the mechanisms driving GHG fluxes from coastal forests under changing environmental conditions. 

Environmental observation networks, such as AmeriFlux, are foundational for monitoring ecosystem response to climate change, management practices, and natural disturbances; however, their effectiveness depends on their representativeness for the regions or continents. We proposed an empirical, time series approach to quantify the similarity of ecosystem fluxes across AmeriFlux sites. We extracted the diel and seasonal characteristics (i.e., amplitudes, phases) from carbon dioxide, water vapor, energy, and momentum fluxes, which reflect the effects of climate, plant phenology, and ecophysiology on the observations, and explored the potential aggregations of AmeriFlux sites through hierarchical clustering. While net radiation and temperature showed latitudinal clustering as expected, flux variables revealed a more uneven clustering with many small (number of sites < 5), unique groups and a few large (> 100) to intermediate (15–70) groups, highlighting the significant ecological regulations of ecosystem fluxes. Many identified unique groups were from under-sampled ecoregions and biome types of the International Geosphere-Biosphere Programme (IGBP), with distinct flux dynamics compared to the rest of the network. At the finer spatial scale, local topography, disturbance, management, edaphic, and hydrological regimes further enlarge the difference in flux dynamics within the groups. Nonetheless, our clustering approach is a data-driven method to interpret the AmeriFlux network, informing future cross-site syntheses, upscaling, and model-data benchmarking research. Finally, we highlighted the unique and underrepresented sites in the AmeriFlux network, which were found mainly in Hawaii and Latin America, mountains, and at under- sampled IGBP types (e.g., urban, open water), motivating the incorporation of new/unregistered sites from these groups.