Cleber Ibraim Salimon

Legacy of fire slows carbon accumulation in Amazonian forest regrowth

Amazonian farmers and ranchers use fire to clear land for agriculture and pasture as part of extensive land-use strategies that have deforested 500 000 km2 over the past 25 years. Ash from burning biomass fertilizes crops and pastures, but declining productivity often occurs after a few years, generally leading to land abandonment and further clearing. Subsequent forest regrowth partially offsets carbon emissions from deforestation, but is often repeatedly cleared and burned. In the first quantitative, basin-wide assessment of the effect of repeated clearing and burning on forest regrowth, our analysis of data from 93 stands at nine locations across the region indicates that stands with a history of five or more fires suffer on average a greater than 50% reduction in carbon accumulation. In the absence of management interventions, Amazonian landscapes dominated by this pronounced legacy of fire are apt to accumulate very little carbon and will remain highly susceptible to recurrent burning.

Estimating the Surface Area of Small Rivers in the Southwestern Amazon and Their Role in CO2 Outgassing

Abstract A recent estimate of CO2 outgassing from Amazonian wetlands suggests that an order of magnitude more CO2 leaves rivers through gas exchange with the atmosphere than is exported to the ocean as organic plus inorganic carbon. However, the contribution of smaller rivers is still poorly understood, mainly because of limitations in mapping their spatial extent. Considering that the largest extension of the Amazon River network is composed of small rivers, the authors’ objective was to elucidate their role in air–water CO2 exchange by developing a geographic information system (GIS)-based model to calculate the surface area covered by rivers with channels less than 100 m wide, combined with estimated CO2 outgassing rates at the Ji-Parana River basin, in the western Amazon. Estimated CO2 outgassing was the main carbon export pathway for this river basin, totaling 289 Gg C yr−1, about 2.4 times the amount of carbon exported as dissolved inorganic carbon (121 Gg C yr−1) and 1.6 times the dissolved organic...

Tree mortality, recruitment and growth in a bamboo dominated forest fragment in southwestern Amazonia, Brazil

Forest fragmentation affects the structure and dynamics of plant communities, leading to biodiversity loss in forest remnants. In this paper we show that in a bamboo (Guadua weberbaueri Pilger) dominated forest fragment in southwestern Amazonia edge effect may be confounded by bamboo effect, which also occur inside the forest. We measured growth, mortality and, recruitment rate of trees with DBH ≥ 10 cm, in a fragment of bamboo dominated open forest in southwestern Amazonia, state of Acre, Brazil, in 15 plots at the forest edge and 15 plots inside the forest fragment, 500 m away from the border. Time interval between censuses was 1.8 years. The average diameter growth rate differed significantly between edge (3.82 ± 0.10 mm a-1) and interior (2.39 ± 0.18 mm a-1); but there were no differences in annual mortality rate (edge = 3.8 ± 2.5 % a-1 CV = 65.7%; interior = 3.6 ± 2.6% a-1 CV = 72.2%) or in annual recruitment rate (edge = 7.1 ± 3.2% a-1 CV = 45%; interior = 8.9 ± 7.9% a-1 CV = 88.7%). Diameter growth rate, particularly of pioneer and fast-growing trees, is favored by the environmental conditions of the edge, where bamboo abundance is higher. However, the absence of an edge effect on mortality and recruitment could be due to the particular dynamics of bamboo patches, which could be mimicking forest edges and therefore masking possible edge effect in this fragment. We speculate that the mortality and recruitment patterns in fragmented forests of southwestern Amazonia is different from other areas in Amazonia and that bamboo is one of the key controllers of successional processes in these fragments.

Drought-induced Amazonian wildfires instigate a decadal-scale disruption of forest carbon dynamics

Drought-induced wildfires have increased in frequency and extent over the tropics. Yet, the long-term (greater than 10 years) responses of Amazonian lowland forests to fire disturbance are poorly known. To understand post-fire forest biomass dynamics, and to assess the time required for fire-affected forests to recover to pre-disturbance levels, we combined 16 single with 182 multiple forest census into a unique large-scale and long-term dataset across the Brazilian Amazonia. We quantified biomass, mortality and wood productivity of burned plots along a chronosequence of up to 31 years post-fire and compared to surrounding unburned plots measured simultaneously. Stem mortality and growth were assessed among functional groups. At the plot level, we found that fire-affected forests have biomass levels 24.8 ± 6.9% below the biomass value of unburned control plots after 31 years. This lower biomass state results from the elevated levels of biomass loss through mortality, which is not sufficiently compensated for by wood productivity (incremental growth + recruitment). At the stem level, we found major changes in mortality and growth rates up to 11 years post-fire. The post-fire stem mortality rates exceeded unburned control plots by 680% (i.e. greater than 40 cm diameter at breast height (DBH); 5–8 years since last fire) and 315% (i.e. greater than 0.7 g cm−3 wood density; 0.75–4 years since last fire). Our findings indicate that wildfires in humid tropical forests can significantly reduce forest biomass for decades by enhancing mortality rates of all trees, including large and high wood density trees, which store the largest amount of biomass in old-growth forests. This assessment of stem dynamics, therefore, demonstrates that wildfires slow down or stall the post-fire recovery of Amazonian forests. This article is part of a discussion meeting issue ‘The impact of the 2015/2016 El Niño on the terrestrial tropical carbon cycle: patterns, mechanisms and implications’.

DINÂMICA DO CARBONO INORGÂNICO DISSOLVIDO NOS RIOS TELES PIRES E CRISTALINO NA BACIA AMAZÔNICA

The rivers are extremely important in the carbon cycle, either inthe CO2 out gassing flows or carbon exporters to the oceans. Directmeasuring of CO2 exchanges between the terrestrial ecosystems and theatmosphere should consider the aquatic systems flows, not overestimatingthe carbon terrestrial accumulation. The Amazon basin has the largest andmore complex system of fresh water in the world, so that it holds animportant in the global carbon cycle. The objective of this work was toevaluate, during the period between September 2004 to August 2005, thedynamics of the Total Dissolved Inorganic Carbon (DIC) and fractions(dissolved CO2 + HCO3 - + CO32 -), in the waters of Teles Pires andCristalino rivers, components of the Amazon basin, in the district of AltaFloresta, MT. Fortnightly were determined DIC concentration, pH andtemperature of the rivers. Based in those results and applying thethermodynamic balance equations, it was possible to estimate the pCO2and the carbonate system fractions. The rivers presented a seasonal variationin the pH values, being closer to the neutrality in the drought period. Theconcentration of HCO3- was significantly larger in the drought than duringthe flood season. Both studied rivers were oversaturated in CO2 related tothe atmosphere.