Carbon Balance and Vegetation Dynamics in an Old‐growth Amazonian Forest

Abstract

Abstract. Amazon forests could be globally significant sinks or sources for atmospheric carbon dioxide, but carbon balance of these forests remains poorly quantified. We surveyed 19.75 ha along four 1-km transects of well-drained old-growth upland forest in the Tapajós National Forest near Santarém, Pará, Brazil (2Њ51Ј S, 54Њ58Ј W) in order to assess carbon pool sizes, fluxes, and climatic controls on carbon balance. In 1999 there were, on average, 470 live trees per hectare with diameter at breast height (dbh) Ն10 cm. The mean (and 95% CI) aboveground live biomass was 143.7 Ϯ 5.4 Mg C/ha, with an additional 48.0 Ϯ 5.2 Mg C/ha of coarse woody debris (CWD). ). The gain in live wood biomass was exceeded by respiration losses from CWD, resulting in an overall estimated net loss from total aboveground biomass of 1.9 Ϯ 1.0 Mg C·ha Ϫ1 ·yr Ϫ1. The presence of large CWD pools, high recruitment rate, and net accumulation of small-tree biomass, suggest that a period of high mortality preceded the initiation of this study, possibly triggered by the strong El Niñ o Southern Oscillation events of the 1990s. Transfer of carbon between live and dead biomass pools appears to have led to substantial increases in the pool of CWD, causing the observed net carbon release. The data show that biometric studies of tropical forests neglecting CWD are unlikely to accurately determine carbon balance. Furthermore, the hypothesized sequestration flux from CO 2 fertilization (Ͻ0.5 Mg C·ha Ϫ1 ·yr Ϫ1 ) would be comparatively small and masked for considerable periods by climate-driven shifts in forest structure and associated carbon balance in tropical forests.

Soil-induced impacts on forest structure drive coarse woody debris stocks across central Amazonia

“…The disks were sub-sampled randomly. Void spaces were taken into account for volume estimation by visually estimating their proportion (Keller et al 2004), but were not used for density correction which may have caused an overestimation of up to 10% in some decay classes (Keller et al 2004;Chao et al 2008).…”

“…Of the different stocks, above-ground biomass is most often assessed in tropical forests, however coarse woody debris (CWD) is also an essential component because of its role in biogeochemical cycles (Chambers et al 2000;Clark et al 2002;Wilcke et al 2005;Palace et al 2008). Within tropical forests, CWD accounts for 6 to 25% of total above-ground carbon stocks (Nascimento and Laurance 2002; Rice et al 2004;Baker et al 2007; Palace et al 2012), implying a total pan-Amazon CWD carbon stock of ca. 10 Pg (Chao et al 2009a).…”

“…10 Pg (Chao et al 2009a). The variation in CWD stocks across the Amazon Basin is thought to be modulated by environmental factors, such as hydrology and soils, and by forest biomass itself (Rice et al 2004;Baker et al 2007;Chao et al 2009). …”

“…Spatial variation in CWD stocks across the landscape may respond both to short-term climatic disturbances (e.g. Phillips et al 2009;Negrón-Juárez et al 2010) and to long-term differences in forest dynamics in response to environmental characteristics (Keller et al 2004;Malhi et al 2006;Chao et al 2009a). Soils represent an important environmental gradient in Amazonia, with a wide variety of soil types across the Basin and with diverse chemical and physical conditions (Quesada et al 2010;.…”

Avaliação da quantidade de resíduos lenhosos em floresta não explorada e explorada com técnicas de redução de impactos, utilizando amostragem por linha interceptadora, no Médio Mojú, Amazônia Oriental, Brasil

“…Levantamentos de Resíduos Lenhosos (RL) têm sido utilizados, para descrever distúrbios nas florestas (Stutevant et al, 1997), na determinação de mudança estrutural da floresta em resposta a diferentes impactos ambientais, na avaliação de diferenças entre locais em termos de produtividade, dinâmica da comunidade, quantidade de carbono biogeoquímico (Harmon & Hua, 1991) e também para avaliação da qualidade e status dos habitats da vida selvagem, para determinar a quantidade de material combustível e procedimentos contra incêndios florestais e para avaliar a quantidade de carbono retido na madeira morta (Fearnside, 1997, Rice et al, 2004. Estudos de resíduos lenhosos também têm sido importantes para explicar a produtividade dos sítios quanto à ciclagem e armazenamento de nutrientes e água e para avaliar a produtividade primária em ecossistemas de florestas tropicais (Malhi et al, 2004).…”