Relative influence of stand and site factors on aboveground live-tree carbon sequestration and mortality in managed and unmanaged forests.

• Use of rare long-term data from multiple experimental forests across northeastern U.S. • Of all stand/site factors considered, stocking was most influential in managed stands. • C sequestration was highest a few years after harvest in managed stands. • Uneven-aged management tended to have positive effects on C sequestration in certain conditions. • Showcases the potential use of uneven-aged management regimes in climate mitigation. We compiled data from several independent, long-term silvicultural studies on USDA Forest Service experimental forests across a latitudinal gradient in the northeastern and north-central U.S.A. to evaluate factors influencing aboveground live-tree carbon sequestration and mortality. Data represent five sites with more than 70,000 repeated tree records spanning eight decades, five ecoregions, and a range of stand conditions. We used these data to test the relative influence of factors such as climate, treatment history (uneven-aged or no management), species composition, and stand structural conditions on aboveground live-tree carbon sequestration and mortality in repeatedly measured trees. Relative to no management, we found that uneven-aged management tended to have a positive effect on carbon sequestration at low stocking levels and in areas of favorable climate (expressed as a combination of growing season precipitation and annual growing degree days > 5 °C). In addition, losses of carbon from the aboveground live-tree pool due to tree mortality were lower in managed than unmanaged stands. These findings suggest that there may be conditions at which rate of sequestration in living trees is higher in stands managed with uneven-aged silviculture than in unmanaged stands, and that this benefit is greatest where climate is favorable. [ABSTRACT FROM AUTHOR]