Search

We compared long-term C sequestration in the pools of aboveground portions of live trees, dead wood, and harvested wood products among highly contrasting forest management scenarios on a rotation (30-100 years) and 100-year basis. Average annual net change in C (AAC) and the cumulative sum of net changes in C were calculated using 65 years of data from permanent plots representing contrasting approaches to managing mixed-species stands dominated by shade-tolerant coniferous species on the Penobscot Experimental Forest in Maine, USA. Simulations of tree growth and mortality were used to estimate C pools to 100 years. On a rotation basis and for all pools combined, scenarios with selection cutting had greater AAC than those with shelterwood cutting followed by thinning or with diameter-limit cutting (p < 0.05). For combined pools, the cumulative sum of net changes in C for the unmanaged, selection, and guiding diameter-limit stands was positive for most of the study period. Our results suggest that strategies that maintain overstory stocking levels necessary to regenerate desired species and promote the development of sawlog-sized trees can enhance long-term C sequestration in mixed-species, naturally regenerated northern temperate forests. [ABSTRACT FROM AUTHOR]

• CO 2 emissions were measured from a spruce stump chronosequence that spanned 0 to 32 years post-harvest. • CO 2 emissions increased from 0 years, peaked ca. 6–8 years, and decreased by 23 years post-harvest. • No clear relationship was found between CO 2 emissions and environmental variables. Understanding the forest carbon cycle has become increasingly important as carbon dioxide (CO 2) 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 CO 2 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 CO 2 flux (3.2 μmol CO 2 m−2 s−1 at year 0) followed by a rapid increase, peaking 8 years post-harvest (24.3 μmol CO 2 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 CO 2 m−2 s−1, respectively). We found no clear relationship between CO 2 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 CO 2 flux rates. The large variability in CO 2 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. [ABSTRACT FROM AUTHOR]