Carbon Accumulation Patterns During Post-Fire Succession in Cajander Larch (Larix cajanderi) Forests of Siberia

Increased fire activity within boreal forests could affect global terrestrial carbon (C) stocks by decreasing stand age or altering tree recruitment, leading to patterns of forest regrowth that differ from those of pre-fire stands. To improve our understanding of post-fire C accumulation patterns within boreal forests, we evaluated above- and belowground C pools within 17 Cajander larch (Larix cajanderi) stands of northeastern Siberia that varied in both years since fire and stand density. Early-successional stands (<20-year old) exhibited low larch recruitment, and consequently, low density, aboveground larch biomass, and aboveground net primary productivity (ANPP _tree). Mid-successional stands (21- to 70-year old) were even-aged with considerable variability in stand density. High-density mid-successional stands had 21 times faster rates of ANPP _tree than low-density stands (252 vs. 12 g C m ^-2 y ^-1) and 26 times more C in aboveground larch biomass (2,186 vs. 85 g C m ^-2). Density had little effect on total soil C pools. During late-succession (>70-year old), aboveground larch biomass, ANPP _tree, and soil organic layer C pools increased with stand age. These stands were low density and multi-aged, containing both mature trees and new recruits. The rapid accumulation of aboveground larch biomass in high-density, mid-successional stands allowed them to obtain C stocks similar to those in much older low-density stands (~8,000 g C m ^-2). If fire frequency increases without altering stand density, landscape-level C storage could decline, but if larch density also increases, large aboveground C pools within high-density stands could compensate for a shorter successional cycle.