Methane Production Explained Largely by Water Content in the Heartwood of Living Trees in Upland Forests

Abstract

Abstract Most forests worldwide are located in upland landscapes. Previous studies have mainly focused on ground methane (CH 4 ) flux in upland forests, and living tree stem‐based CH 4 processes and fluxes are thus relatively poorly understood. This study investigated the relationship between CH 4 concentration and water content in the heartwood of living trees in midtemperate, warm temperate, and subtropical upland forests and also measured seasonal changes of in situ stem CH 4 flux and the CH 4 concentration and water content in the heartwood of Populus davidiana Dode in a warm temperate upland forest. We found that approximately 4–13% of tree stems or approximately 8–31% of tree species had a substantial CH 4 concentration of ≥10,000 μL L −1 in their heartwood across the three types of upland forests. The heartwood CH 4 concentration was related to water content by a power function. A threshold of water content occurred beyond which CH 4 was produced at high levels in the heartwood. The CH 4 emissions from the breast height stems of P. davidiana ranged from 202.1 to 331.6 μg m −2 h −1 on a stem surface area basis during July–October 2016 and were significantly linearly correlated with the CH 4 concentration or water content in the heartwood throughout the experimental period, but the linear correlation was not significant at daily and monthly scales. Temperature was not a limiting factor for CH 4 production during July–October 2016, and thus, most of the CH 4 production may be explained by water content in the heartwood of living trees in upland forests.