Carbon storage and long-term dynamics in old-growth forests across the Central Hardwood Region
Forests play a primary role in mitigating against the accumulation of atmospheric greenhouse gases by consuming carbon dioxide and storing carbon in a variety of long-term pools. Although old-growth forests were long thought to be composed of senescent, slow growing individuals, contemporary research suggests that these forests vigorously consume carbon and may store carbon at faster rates than their younger counterparts. While carbon storage has received a great deal of study in many forest regions, such as the Pacific Northwest, other regions have received less attention, leaving gaps in our understanding of carbon dynamics across North American forests. For example, little is known about carbon storage in the forests of the Central Hardwood Region. However, the high productivity of these forests, and the fact that many are approaching advanced stages of development, suggest that the Central Hardwood Region may be important to terrestrial carbon sequestration. Therefore, examining storage capacity across the Region’s productivity gradient is critical to understanding contemporary carbon storage and future storage potential. Above- and belowground data representing a network of permanent plots was used to investigate carbon storage pools along a regional productivity gradient and to describe the changes in those pools over the last 20 years.
Total aboveground live tree carbon ranged between 89.0 Mg C ha-1 and 164.7 Mg C ha-1, which increased with productivity along a gradient from southwest to northeast; significant differences were observed among sites along the gradient. Aboveground carbon in live trees was stable over the last 20 years within all sites. Carbon estimates of downed woody debris (≥ 10 cm diameter) ranged between 5.4 Mg C ha-1 and 15.5 Mg C ha-1, which increased similarly with productivity along the southwest to northeast gradient. Mass of downed woody debris carbon pools increased significantly over the last 20 years within the mesic sites located in the northeast, driven by a shift in species dominance from Quercus and Carya species to Acer and Fagus species and the resulting recruitment of downed woody debris. Regional carbon storage estimates of U.S. Forest Service properties range between 109.5 Mg C ha-1 (Great Plains) and 254.4 Mg C ha-1 (Pacific Northwest), indicating that, when considering the additional carbon contributed by belowground components, total carbon stores in old-growth CHR forests are critical to terrestrial carbon sequestration and atmospheric greenhouse gas mitigation strategies.