CO2 flux from Acer saccharum logs: Sources of variation and the influence of silvicultural treatments

Abstract

Several aspects of the forest carbon cycle have not been examined in detail, including sources of variation in carbon dioxide (CO₂) emissions from coarse woody material (CWM). To address this knowledge gap, we examined CO₂ emissions from Acer saccharum logs within four harvesting treatments, using closed chambers fitted to the logs. We found that CO₂ emissions were highest for logs in small (31.8 ± 20.4 μmol CO₂ m^-3 s^-1) and large gaps (29.6 ± 24.4 μmol CO₂ m^-3 s^-1) compared to those in control (13.9 ± 8.3 μmol CO₂ m^-3 s^-1) and thinned matrix (13.6 ± 8.0 μmol CO₂ m^-3 s^-1) treatments. CO₂ flux rates did not differ between gap sizes, but they increased with temperature, which was higher in the small gap treatment. In addition, two individual logs fitted with multiple closed chambers revealed significant within-log variability in CO₂ emissions. On a subset of logs repeatedly sampled throughout the day, we found that log surface temperature generally peaked at midday and was positively correlated with CO₂ emissions, although this relationship was weak in one log. This study provides insight into sources of variation in CO₂ emissions from CWM, while improving our understanding of the forest carbon cycle.