Methane emissions from tree stems: a new frontier in the global carbon cycle.

Tree stems from wetland, floodplain and upland forests can produce and emit methane (CH ). Tree CH stem emissions have high spatial and temporal variability, but there is no consensus on the biophysical mechanisms that drive stem CH production and emissions. Here, we summarize up to 30 opportunities and challenges for stem CH emissions research, which, when addressed, will improve estimates of the magnitudes, patterns and drivers of CH emissions and trace their potential origin.