Tree stem methane flux, tomography, and microtopography data from Harvard Forest upland and wetland sites, 2023-2025

This data package contains tree stem methane (CH4) and carbon dioxide (CO2) flux measurements, wood tomography assessments, and microtopography classifications from Harvard Forest, Petersham, Massachusetts, USA. Data were collected from June 2023 to October 2025 at two contrasting forest sites: the Black Gum Swamp (BGS) wetland and the Environmental Measurement Station (EMS) upland forest on the Prospect Hill tract. Stem greenhouse gas fluxes were measured on 60 trees (30 per site) spanning four species: black gum (Nyssa sylvatica), red maple (Acer rubrum), eastern hemlock (Tsuga canadensis), and red oak (Quercus rubra). Fluxes were quantified using static closed chambers coupled to a Los Gatos Research Ultra-Portable Greenhouse Gas Analyzer (UGGA). The dataset includes 1,640 quality-controlled flux observations with associated R-squared values, standard errors, and measurement metadata. CH4 flux units are reported in nmol m-2 s-1 and CO2 fluxes in micromol m-2 s-1. Internal wood condition was assessed non-destructively for all 60 study trees using PiCUS sonic tomography (SoT) and electrical resistance tomography (ERT) at breast height (1.37 m). Summary statistics of resistivity and sound wood percentage are provided alongside cross-section images for each tree. Microtopographic position (hummock, hollow, or intermediate) was classified for the 30 wetland trees based on field assessment of tree base elevation relative to the surrounding peat surface.