Estimating the multi-decadal carbon deficit of burned Amazonian forests

Abstract

Wildfires in humid tropical forests have become more common in recent years, increasing the rates of tree mortality in forests that have not co-evolved with fire. Estimating carbon emissions from these wildfires is complex. Current approaches rely on estimates of committed emissions based on static emission factors through time and space, yet these emissions cannot be assigned to specific years, and thus are not comparable with other temporally-explicit emission sources. Moreover, committed emissions are gross estimates, whereas the long-term consequences of wildfires require an understanding of net emissions that accounts for post-fire uptake of CO2. Here, using a 30 year wildfire chronosequence from across the Brazilian Amazon, we calculate net CO2 emissions from Amazon wildfires by developing statistical models comparing post-fire changes in stem mortality, necromass decomposition and vegetation growth with unburned forest plots sampled at the same time. Over the 30 yr time period, gross emissions from combustion during the fire and subsequent tree mortality and decomposition were equivalent to 126.1 Mg CO2 ha−1 of which 73% (92.4 Mg CO2 ha−1) resulted from mortality and decomposition. These emissions were only partially offset by forest growth, with an estimated CO2 uptake of 45.0 Mg ha−1over the same time period. Our analysis allowed us to assign emissions and growth across years, revealing that net annual emissions peak 4 yr after forest fires. At present, Brazil’s National Determined Contribution (NDC) for emissions fails to consider forest fires as a significant source, even though these are likely to make a substantial and long-term impact on the net carbon balance of Amazonia. Considering long-term post-fire necromass decomposition and vegetation regrowth is crucial for improving global carbon budget estimates and national greenhouse gases (GHG) inventories for tropical forest countries.

Drought-driven wildfire impacts on structure and dynamics in a wet Central Amazonian forest

“…Continued monitoring of these plots in regular intervals (annual or biannual) is important to improve our understanding of the related carbon fluxes (emissions and uptake) [ 58 ], the recovery time to pre-fire states [ 20 ] and/or eventual disruption of carbon dynamics by tree mortality (e.g. caused by additional drought and fire events) [ 59 ].…”

Assessing the carbon capture potential of a reforestation project

“…Growing forests are subject to numerous threats. The frequency of wildfire has increased in rainforests over the past decades 55 . While it is agreed that wildfires have a major negative impact on forest carbon stocks 56 , accounting for all potential effects of the fire on the regrowth of a forest plot is difficult 55 .…”

“…The frequency of wildfire has increased in rainforests over the past decades 55 . While it is agreed that wildfires have a major negative impact on forest carbon stocks 56 , accounting for all potential effects of the fire on the regrowth of a forest plot is difficult 55 . Although wildfires happen predominantly on old growth forest, with more dead material in old growth forests compared to secondary forests 57 , tree mortality has increased in young secondary forests, particularly in the western and southern Amazon 58 .…”

Beyond Deforestation: Carbon Emissions From Land Grabbing and Forest Degradation in the Brazilian Amazon

“…Measuring and monitoring forest degradation/disturbance present some unique challenges: many processes happen below the forest canopy (Matricardi et al, 2020) and their emissions can be lagged, occurring years or even decades after the initial disturbance. Recent advances in mapping, monitoring, and attribution of forest fires, the largest source of degradation and disturbance, may help address these challenges (Curtis et al, 2018;de Azevedo et al, 2018;Andela et al, 2019;MapBiomas, 2020;Silva et al, 2020). Using new spatial datasets to track degradation and emissions from forest fires could be a good starting point, complemented by ongoing efforts to map other types of forest degradation (e.g., selective logging, extreme droughts, mining) and land-use changes (e.g., MapBiomas, 2020) over time.…”