Development of ecosystem structure and function on reforested surface-mined lands in the Central Appalachian Coal Basin of the United States

Abstract

Surface mining in the Appalachian Coal Basin drastically disturbs the landscape. Post-mining reforestation efforts have reached reliable tree survivability and growth; however, it is unclear whether these reforestation efforts also restore the ecological functions associated with the native forest ecosystem. The objectives of this study were to quantify the rate at which certain key ecosystem functions return to the landscape, and to relate the development of those functions to structural attributes of the ecosystem. A chronosequence of four reclaimed and reforested stands (ages 5, 11, 21 and 30 years) and unmined reference stands representing pre-mining conditions, were identified on the Appalachian Plateau in southwestern Virginia. Total soil nitrogen (N) and component (mineral soil, forest floor, root, and aboveground biomass) ecosystem carbon (C) pools were quantified. Throughout the growing season, monthly samples for soil gas fluxes [i.e., carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4)], available inorganic-N [nitrate (NO3 −) and ammonium (NH4 +)], and total and active microbial biomass were measured. As expected, soil organic C (SOC) and total ecosystem C returned to the mined landscape, although at levels still less than half of the unmined reference after 30 years. Ecosystem C accumulation was significantly correlated with soil N (r = 0.80; p = 0.0003) as well as total and active microbial biomass (r = 0.92; p = <0.0001 and r = 0.86; p = <0.0001, respectively). Surprisingly, available inorganic-N and gas fluxes of CO2 and N2O showed no significant differences among any of the mined and unmined stands; however, the reforested mined soils showed a significantly diminished capacity for CH4 uptake, where upland soils typically represent the largest global biogenic sink of atmospheric CH4. Thus, although many ecosystem components (e.g., forest and microbial biomass) and functions (e.g., N cycling), rapidly returned to the reclaimed landscape, some critical ecosystem functions (e.g., methanotrophy) exhibited a fundamentally different rate of return, if present at all. Our results indicate that reforestation of native hardwoods on reclaimed surface mined lands is largely successful at restoring many ecosystem functions, but that certain functional attributes are decoupled from the observed redevelopment of ecosystem structure. Thus, reforestation and forest ecosystem restoration are not necessarily the same thing, and a better understanding of potential disconnects between the two concepts can be critical in guiding both the science and the practice into the future.