Tree mode of death and mortality risk factors across Amazon forests

The carbon sink capacity of tropical forests is substantially affected by tree mortality.However, the main drivers of tropical tree death remain largely unknown. Here we present a pan-Amazonian assessment of how and why trees die, analysing over 120,000 trees representing > 3800 species from 189 long-term RAINFOR forest plots. While tree mortality rates vary greatly Amazon-wide, on average trees are as likely to die standing as they are broken or uprooted—modes of death with different ecological consequences. Species-level growth rate is the single most important predictor of tree death in Amazonia, with faster growing species being at higher risk. Within species, however, the slowest-growing trees are at greatest risk while the effect of tree size varies across the basin. In the driest Amazonian region species-level bioclimatic distributional patterns also predict the risk of death, suggestingthat these forests are experiencing climatic conditions beyond their adaptative limits.These results provide not only a holistic pan-Amazonian picture of tree death but largescale evidence for the overarching importance of the growth–survival trade-off in driving tropical tree mortality

Drought and ecosystem carbon cycling

Drought as an intermittent disturbance of the water cycle interacts with the carbon cycle differently than the ‘gradual’ climate change. During drought plants respond physiologically and structurally to prevent excessive water loss according to species-specific water use strategies. This has consequences for carbon uptake by photosynthesis and release by total ecosystem respiration. After a drought the disturbances in the reservoirs of moisture, organic matter and nutrients in the soil and carbohydrates in plants lead to longer-term effects in plant carbon cycling, and potentially mortality. Direct and carry-over effects, mortality and consequently species competition in response to drought are strongly related to the survival strategies of species. Here we review the state of the art of the understanding of the relation between soil moisture drought and the interactions with the carbon cycle of the terrestrial ecosystems. We argue that plant strategies must be given an adequate role in global vegetation models if the effects of drought on the carbon cycle are to be described in a way that justifies the interacting processes

Soil physical constraints as a limiting factor of palm and tree basal area in amazonian forests

Background: Trees and arborescent palms adopt different rooting strategies and responses to physical limitations imposed by soil structure, depth and anoxia. However, the implications of these differences for understanding variation in the relative abundance of these groups have not been explored. Aims: We analysed the relationship between soil physical constraints and tree and palm basal area to understand how the physical properties of soil are directly or indirectly related to the structure and physiognomy of lowland Amazonian forests. Methods: We analysed inventory data from 74 forest plots across Amazonia, from the RAINFOR and PPBio networks for which basal area, stand turnover rates and soil data were available.We related patterns of basal area to environmental variables in ordinary least squares and quantile regression models. Results: Soil physical properties predicted the upper limit for basal area of both trees and palms. This relationship was direct for palms but mediated by forest turnover rates for trees. Soil physical constraints alone explained up to 24% of palm basal area and, together with rainfall, up to 18% of tree basal area. Tree basal area was greatest in forests with lower turnover rates on well-structured soils, while palm basal area was high in weakly structured soils. Conclusions: Our results show that palms and trees are associated with different soil physical conditions. We suggest that adaptations of these life-forms drive their responses to soil structure, and thus shape the overall forest physiognomy of Amazonian forest vegetation

Soil physical constraints as a limiting factor of palm and tree basal area in amazonian forests

Background: Trees and arborescent palms adopt different rooting strategies and responses to physical limitations imposed by soil structure, depth and anoxia. However, the implications of these differences for understanding variation in the relative abundance of these groups have not been explored. Aims: We analysed the relationship between soil physical constraints and tree and palm basal area to understand how the physical properties of soil are directly or indirectly related to the structure and physiognomy of lowland Amazonian forests. Methods: We analysed inventory data from 74 forest plots across Amazonia, from the RAINFOR and PPBio networks for which basal area, stand turnover rates and soil data were available.We related patterns of basal area to environmental variables in ordinary least squares and quantile regression models. Results: Soil physical properties predicted the upper limit for basal area of both trees and palms. This relationship was direct for palms but mediated by forest turnover rates for trees. Soil physical constraints alone explained up to 24% of palm basal area and, together with rainfall, up to 18% of tree basal area. Tree basal area was greatest in forests with lower turnover rates on well-structured soils, while palm basal area was high in weakly structured soils. Conclusions: Our results show that palms and trees are associated with different soil physical conditions. We suggest that adaptations of these life-forms drive their responses to soil structure, and thus shape the overall forest physiognomy of Amazonian forest vegetation

Dinâmica estrutural da comunidade lenhosa em Floresta Estacional Semidecidual na transição Cerrado-Floresta Amazônica, Mato Grosso, Brasil Structural dynamics of the woody community in a semideciduous forest in the Cerrado-Amazon Forest transition of Mato Grosso, Brazil

O entendimento de processos ecológicos, especialmente das modificações estruturais e florísticas em ecossistemas naturais, é fundamental para embasar ações visando à sua conservação e/ou restauração. O objetivo do estudo foi avaliar mudanças ocorridas na estrutura da comunidade lenhosa na transição Cerrado-Floresta Amazônica, no período de 2003 a 2008. Foram estabelecidas 60 parcelas permanentes de 10 x 10 m onde foram amostrados todos os indivíduos com diâmetro à altura do peito > 5 cm. Em 2003 foram registrados 1.140 ind. ha-1 e área basal de 24,35 m² ha-1, enquanto em 2008 foram 1.071 ind. ha-1 e área basal de 22,04 m² ha-1. O recrutamento (2,76% ano-1) não compensou a mortalidade (3,95% ano-1) e o ganho em área basal (0,54% ano-1) não superou a perda (3,77% ano-1). Em função dessa diferença, a meia vida (17,3 anos) foi menor que o tempo de duplicação (29,9 anos), resultando em baixa estabilidade (12,6 anos) e reposição (23,6 anos) em relação a outras florestas estacionais. Os parâmetros de dinâmica da comunidade e das principais espécies sugerem que a floresta está passando por mudanças caracterizadas principalmente pela retração da densidade e biomassa dos indivíduos arbóreos, que podem estar relacionadas ao aumento das lianas, a uma fase de início de reconstrução do ciclo silvigenético da floresta ou ainda à forte seca que ocorreu na região no ano de 2005.<br>Understanding ecological processes, especially the structural and floristic changes in natural ecosystems, is essential before conserving and/or restoring these areas. The aim of this study was to assess the changes that occurred in the woody plant community from 2003 to 2008. Sixty permanent plots of 10 x 10 m were established, in which all individuals with diameter at breast height > 5 cm were sampled. A total of 1,140 ind. ha-1 were recorded in 2003 (basal area 24.35 m² ha-1) and 1,071 ind. ha-1 in 2008 (basal area of 22.04 m² ha-1). The recruitment (2.76% year-1) did not compensate mortality (3.95% year-1) and the basal area gain (0.54% year-1) did not exceed the loss (3.77% year-1). Because of this unbalance, the half-life (17.3 years) was lower than the doubling time (29.9 years), resulting in low stability (12.6 yrs) and replacement (23.6 yrs) in relation to other seasonal forests. The parameters of community and species dynamics suggest that the forest is undergoing changes characterized mainly by the density and biomass reduction of trees, which may be related to an increase in lianas, an early rebuilding phase of the forest silvigenetic cycle or even the severe drought that occurred in the region in 2005