Impacts of fire severity and post-fire reforestation on carbon pools in boreal larch forests in Northeast China

Abstract

Aims: Boreal larch (Larix gmelinii) forests in Northeast China have been widely disturbed since the 1987 conflagration; however, its long-term effects on the forest carbon (C) cycling have not been explored. The objective of this study thus was to quantify the effects of fire severity and post-fire reforestation on C pools and the changes of these forests. Methods: Sixteen permanent plots have been set in two types of larch stands (L. gmelinii-grass, LG; and L. gmelinii-Rhododendron dahurica, LR) with three levels of fire severity (unburned, low-severity and high-severity but replanted), at 1987 burned sites in Daxing'anling, northeastern China, to repeatedly measure ecosystem C pools in 1998 and 2014. C components were partitioned into vegetation (foliage, branch, stem and roots), soil and detritus (standing and fallen woody debris and litter). The fire effects on post-fire C dynamics were examined by comparing the differences of C pools and changes between the two field investigations caused by fire severity. Important Findings: During the study period, unburned mature stands were C sinks (105g C m-2 year-1 for LG, and 190g C m-2 year-1 for LR), whereas the low-severity stands were C-neutral (-4 and 15g C m-2 year-1 for LG and LR, respectively). The high-severity burned but reforested stands were C sinks, among which, however, magnitudes (88 and 16g C m-2 year-1 for LG and LR, respectively) were smaller than those of the two unburned stands. Detritus C pools decreased significantly (with a loss ranging from 26 to 38g C m-2 year-1) in the burned stands during recent restoration. Soil organic C pools increased slightly in the unmanaged stands (unburned and low-severity, with accumulation rates ranging from 4 to 35g C m-2 year-1), but decreased for the high-severity replanted stands (loss rates of 28 and 36g C m-2 year-1 for LG and LR, respectively). These results indicate that fire severity has a dynamic post-fire effect on both C pools and distributions of the boreal larch forests, and that effective reforestation practice accelerates forest C sequestration.