Carbon dynamics in old-growth forests of the Central Hardwoods Region, USA

Abstract

Managing old-growth forests and promoting old-growth complexity in aging forests for carbon emissions mitigation has become an important component of diversified land management strategies. In the midwestern US, the Central Hardwoods Region (CHR) is the largest continuous deciduous forested area and includes a diverse range of species compositions, forest structures, and topoedaphic environments. Understanding carbon storage potential in old-growth forests across the CHR is important for evaluating climate-adaptive management strategies to increase carbon sequestration in the region’s aging forests. We assessed forest carbon in two time periods (the early 1990s and the 2010s) in ten old-growth forests across a 770 km east-west productivity gradient from Indiana to Missouri. Further, we related anomalies in carbon pools between the two sampling periods to documented or observable disturbances. As expected, old-growth forests on more productive sites in the eastern portion of the study range stored more aboveground carbon (120–177 Mg C ha−1) than less productive sites to the west (93–117 Mg C ha−1). Over the twenty-year period, old-growth forests accumulated 9.2 ± 1.5 (mean ± SE) Mg C ha−1 or a 7 % increase in total aboveground carbon. Further, downed dead wood carbon increased 5 % (0.4 ± 0.7 Mg C ha−1), standing dead increased 7 % (0.3 ± 0.7 Mg C ha−1), live roots increased 4 % (1.0 ± 0.3), and dead roots increased by 68 % (0.3 ± 0.1 Mg C ha−1). However, stochastic disturbances can positively or negatively impact total carbon and carbon pools. Documenting carbon trends and disturbance effects in old-growth forests provides guidance to enhance the representation of structurally complex, late successional forests using active forest management. Old-growth forests are currently rare in the CHR landscape, but the abundance of aging forests in the region provides immense potential to store carbon, particularly when combined with strategies that optimize early- and late-successional habitats for carbon sequestration along with other ecological goods and services.