Stem CO2 efflux (EA) significantly contributes to autotrophic and ecosystem respiration in tropical forests, but field methodologies often introduce biases and uncertainty. This study evaluates these biases and their impact on scaling EA at the stand-level. Diel and vertical patterns of EA were investigated, along with the accuracy of estimating stem surface area from allometric equations vs terrestrial light dection and ranging (LiDAR) scanning (TLS) in Maliau Basin Conservation Area, Sabah, Malaysian Borneo. Diel EA exhibited no uniform pattern due to inter-tree variability, but results suggest measuring EA before 15:00 h. EA was significantly higher on buttresses and above the first major branching point, but vertical variations in EA did not impact stand-level EA when stem surface area was accurately estimated. Allometric equations underestimated total stem surface area by c. 40% compared with TLS, but applying a site-specific correction factor yielded a similar stand-level EA and total stem surface area to TLS. This study provides guidance for measuring EA in the field and suggests that measuring at one time point and one height along the stem can produce accurate results if conducted using the correct time frame and if stem surface area is accurately estimated.
Stem respiration constitutes a substantial proportion of autotrophic respiration in forested ecosystems, but its drivers across different spatial scales and land-use gradients remain poorly understood. This study quantifies and examines the impact of logging disturbance on stem CO2 efflux (EA) in Malaysian Borneo. EA was quantified at tree- and stand-level in nine 1-ha plots over a logging gradient from heavily logged to old-growth using the static chamber method. Tree-level results showed higher EA per unit stem area in logged vs old-growth plots (37.0 ± 1.1 vs 26.92 ± 1.14 g C m-2 month-1). However, at stand-level, there was no difference in EA between logged and old-growth plots (6.7 ± 1.1 vs 6.0 ± 0.7 Mg C ha-1 yr-1) due to greater stem surface area in old-growth plots. Allocation to growth respiration and carbon use efficiency was significantly higher in logged plots. Variation in EA at both tree- and stand-level was driven by tree size, growth and differences in investment strategies between the forest types. These results reflect different resource allocation strategies and priorities, with a priority for growth in response to increased light availability in logged plots, while old-growth plots prioritise maintenance and cell structure.