Dynamics of Postfire Aboveground Carbon in a Chronosequence of Chinese Boreal Larch Forests

Abstract

Boreal forests store a large proportion of the global terrestrial carbon (C), while wildfire plays a crucial role in determining their C storage and dynamics. The aboveground C (AC) pool is an important component of forest C stocks. To quantify the turning point (transforming from C source to C sink) and recovery time of postfire AC, and assess how stand density affects the AC, 175 plots from eight stand age classes were surveyed as a chronosequence in the Great Xing'an Mountains of Northeast China. Linear and nonlinear regression analyses were conducted to describe postfire AC recovery patterns. The results showed that (1) postfire AC exhibited a skewed U-shaped pattern with the turning point at approximately year 30, when the change rate of AC shifted from negative to positive, (2) it took more than 120 years for this forest ecosystem to recover 80% of AC in unburned old-growth (200 years) stands, and (3) there was an overall positive relationship between AC and stand density over the entire range of stand age classes; and such relationship was stronger during the early-and late-successional stages, but weaker (p > 0.05) during the midsuccessional stage. Although boreal larch forests have been C sinks under historical fire free intervals, predicted increases in fire frequency could potentially shift it to a C source. Understanding postfire AC dynamics in boreal larch forests is central to predicting C cycling response to wildfire and provides a framework for assessing ecosystem resilience to disturbance in this region. Plain Language SummaryBoreal forests store more than 32% of total global forest carbon (C), but this C pool is very susceptible to wildfires which are one of the most pervasive disturbances in the boreal biome. Identifying the dynamic trajectory and recovery pattern of postfire aboveground C (AC) storage is crucial for understanding the global ecological significance of wildfire disturbance. A total of 175 plots from eight stand age classes were surveyed in the Great Xing'an Mountains of Northeast China to quantify ecological resilience, and further examine the relationship between various components of AC and stand density throughout successional stages. Our data analysis showed that the AC pool could be a C source to the atmosphere for several decades following fire disturbances; and it would take more than a century for the AC to recover 80% of that in old-growth boreal larch forests in Northeastern China. Increases in fire frequency due to climate change and human activities will increase C emission, which may significantly influence the regional C budget. Stand density was considered as a positive factor on AC accumulation following wildfire, but this effect may be counteracted by variation in tree size due to site productivity in other successional stages. Key Points:• Postfire dynamics of aboveground carbon storage were depicted over a 200-year chronosequence in boreal larch forests • Aboveground carbon transformed from a source to a sink after 30 years, and it took over 120 years to recov...

Carbon Emission and Redistribution among Forest Carbon Pools, and Change in Soil Nutrient Content after Different Severities of Forest Fires in Northeast China

“…Boreal forests, one of the largest terrestrial biomes, store 32% of global carbon stocks [1] and play a significant role in global carbon cycles and balance [2][3][4]. Forest carbon is held in six primary pools: standing live trees (SLT), standing dead trees (SDT), coarse woody debris (CWD), shrubs and herbaceous vegetation (S&H), forest floors (litter and duff), and mineral soils [5].…”

“…Forest carbon is held in six primary pools: standing live trees (SLT), standing dead trees (SDT), coarse woody debris (CWD), shrubs and herbaceous vegetation (S&H), forest floors (litter and duff), and mineral soils [5]. Wildland fire is a crucial factor that influences boreal forest structures and development [2,6], especially under climate change conditions with increases in fire size, frequency, and severity [7][8][9][10]. Wildfires not only emit carbon during combustion but also induce carbon transfers and redistribution among these carbon pools (e.g., shifting from live biomass to dead) [11][12][13].…”

“…However, the number of reports on postfire carbon redistribution among forest pools was relatively few compared to forest fire carbon emission research [19][20][21][22], which is not our major focus in this study. However, a few researchers have studied the woody dynamics among forest carbon pools in Canada, America, and northeastern China [2,10,13,23] one or two years post-fire. There is a knowledge gap regarding how much carbon is redistributed between the live pools (e.g., SLT or S&H); dead pools (SDT, CWD, litter, or duff); and soil carbon pools immediately after fires of varying severities.…”

The Relevance of Pyrogenic Carbon for Carbon Budgets From Fires: Insights From the FIREX Experiment

“…As global warming and anthropogenic land use change continue to affect environmental conditions at the land surface, including temperature, humidity, drought frequency, and ignition risk, it is projected that the significance of fire in driving biogeochemical cycles will increase in many regions across the world (Abatzoglou et al, 2018;Turco et al, 2018). Consequently, there is a growing appreciation that precise measurements of fire effects on terrestrial C stocks are critical to projecting the future global dynamics of C in the Earth System (Landry & Matthews, 2017;Surawski et al, 2016;Yang et al, 2015). Most exercises for calculating, modeling, and forecasting fire emissions use the "consumed biomass" approach, which assumes that all burnt C is emitted as gases and aerosols (Surawski et al, 2016).…”

“…Vegetation fires currently emit an estimated 2.2 × 10 15 Pg of C directly into the atmosphere per year (Van Der Werf et al, 2017). In addition, they redistribute C between ecosystem pools by, for example, transferring C from the aboveground living to the dead vegetation pools (Yang et al, 2018). From an ecological perspective, fire can change ecosystem succession or even result in shifts between ecosystem types, consequently altering ecosystem C storage capacity (Gao et al, 2018; Millar & Stephenson, 2015).…”