Temporal trends in CO2 emissions from Picea rubens stumps: A chronosequence approach

Abstract

Understanding the forest carbon cycle has become increasingly important as carbon dioxide (CO2) emissions contribute to the changing climate. Decomposition is a major component of the forest carbon cycle; however, aspects of wood decomposition remain poorly understood, especially for stumps. To fill this knowledge gap, we examined the change in CO2 emissions over time from Picea rubens Sarg. (red spruce) stumps using a 32-year chronosequence (i.e., 0, 2, 4, 8, 23, and 32 years since harvest) derived from detailed harvesting records in a northern conifer forest in central Maine, USA, that has experienced repeated partial harvests. We found low initial CO2 flux (3.2 μmol CO2 m−2 s−1 at year 0) followed by a rapid increase, peaking 8 years post-harvest (24.3 μmol CO2 m−2 s−1) followed in turn by a decrease to very low rates by years 23 and 32 (1.4 and 1.7 μmol CO2 m−2 s−1, respectively). We found no clear relationship between CO2 emissions and any of the environmental or stump variables tested (wood temperature, wood moisture, soil moisture, and/or stump volume), suggesting that time since harvest was the overriding influence on CO2 flux rates. The large variability in CO2 flux rates among stumps of the same time since harvest points to the need for future research that includes larger sample sizes and covers a wider range of environmental and stump variables to better capture potential sources of variation. Our results add to the growing body of research on carbon emissions from deadwood that can inform forest carbon-cycle models. In addition, forest managers, who are increasingly interested in carbon management, can use these results to assess harvesting impacts on forest carbon emissions.