Year: 2026
Type: article
Abstract: Key message Stem CO 2 efflux varies in the vertical profile depending mostly on the variability in stem growth rate and the vertical pattern changes with tree age. Abstract Stem CO 2 efflux ( E A ) from trees exhibits both temporal and vertical variability. E A is often measured only at the breast height, making it challenging to accurately upscale these measurements to represent the entire ecosystem. This study examines the potential drivers behind the E A vertical variability and evaluates the long-term changes in the E A ratio between two fixed heights. E A was monitored in two Norway spruce trees over eight growing seasons within a ten-year period (2005–2014). Measurements were carried out simultaneously at three heights (1.3, 3.2, and 4.5 m since 2005 till 2009 and 1.3, 4.5, and 7.5 m since 2011 till 2014) using an automated chamber system. Moreover, meteorological measurements and wood formation analyses were provided. Overall, E A generally increased with the height, though the pattern differed between trees. Assuming that E A at 1.3 m was representative of the whole stem resulted in underestimating the seasonal temperature-normalized E A by 5.3% in one tree and 16.6% in the other. Such variation makes it difficult to generalize the findings. A stem temperature gradient along the stem would contribute to a maximum increase in E A of 4.3%. Conversely, sap flow, which is understood to transport produced CO 2 to the upper parts of the stem, had no apparent effect on the vertical variation of E A . Our findings suggest that the vertical variation in E A is primarily driven by the differences in stem growth, with the stem positions below the crown clearly distinguishable from those at the crown base and within the crown. Moreover, the differences in E A between 4.5 m and 1.3 m were not constant, showing a gradual decrease over time. This adds further uncertainty when generalizing observed vertical E A patterns over longer timescales.
Source: Trees
Language: English
Subfield: Global and Planetary Change
Field: Environmental Science
Domain: Physical Sciences
SDG: Climate action
Open Access status: hybrid
Estimated APC paid: $3,690
OpenAlex ID: W7130705111