Tree stem methane emissions are gaining increasing attention as an overlooked atmospheric source pathway. Existing methods for measuring tree stem greenhouse gas fluxes and isotopes may provide robust integrated emission estimates, but due to their coarse resolution, the capacity to derive insights into fine-scale dynamics of tree stem emissions is limited. We demonstrate and field test an alternative method that is Small, Nimble, In situ and allows for Fine-scale Flux (‘SNIFF’) measurements, on complex and contrasting stem surfaces. It is lightweight and therefore suitable to remote field locations enabling real-time data observations allowing for field-based, data driven sampling regimes. This method facilitated novel results capturing fine-scale vertical and radial methane flux measurements (5 cm increments) and revealed: (1) 86–89% of methane emissions emanated from the lower 30 cm of sampled wetland tree species; (2) clear vertical and horizontal trends in δ¹³C-CH₄ possibly due to fractionation associated with oxidation and/or mass-dependant fractionation during diffusive transport; and (3) the occurrence of substantial radial heterogeneity. We also compared a variety of up-scaling approaches to estimate methane flux per tree, including novel smartphone 3D photogrammetry that resulted in substantially higher stem surface area estimations (> 16 to 36%) than traditional empirical methods. Utilising small chambers with high radial and vertical resolution capabilities may therefore facilitate more robust future assessments into the drivers, pathways, oxidation sinks and magnitude of tree stem greenhouse gas emissions, and compliment previous broad-scale sampling techniques.

作为一种被忽视的大气源途径，树木的甲烷排放量越来越受到关注。现有的用于测量树干温室气体通量和同位素的方法可能会提供可靠的综合排放估算值，但是由于其分辨率较粗糙，因此无法获得深入了解树干排放的尺度动态的能力。我们演示并现场测试了另一种方法，该方法小，灵活，就地，并且可以在复杂且对比鲜明的茎表面上进行精细通量（'SNIFF'）测量。它重量轻，因此适用于远程现场，可进行实时数据观察，从而实现基于现场的数据驱动采样方案。该方法促进了新颖的结果捕获精细的垂直和径向甲烷通量测量值（增量为5 cm），并揭示了：（1）采样的湿地树种的下30厘米排放的甲烷中有86-89％来自甲烷；（2）明确δ的纵横趋势¹³ C-CH ₄可能是由于在扩散运输过程中与氧化和/或质量相关的分馏有关的分馏；（3）发生大量的径向异质性。我们还比较了各种评估每棵树的甲烷通量的放大方法，包括新颖的智能手机3D摄影测量法，该方法得出的茎表面积估计值比传统经验方法高得多（> 16％到36％）。因此，利用具有高径向和垂直分辨率功能的小室可以促进将来对驱动器，途径，氧化沉和树茎温室气体排放量的评估更加可靠，并补充以前的大规模采样技术。